The physical properties of gas phase metal monoacetylide (MCCH, where M = Sc–Zn) molecules have been evaluated with coupled cluster theory and multireference configuration interaction. Metal monoacetylides are isovalent to well-studied metal monocyanides (MCN) and metal monoisocyanides (MNC), which suggests the MCCH series will have similar electronic structure. Some of the MCCH molecules, such as ScCCH, FeCCH, and CoCCH share a trait with their isoelectronic MCN/MNC counterparts: profound multireference character and low-lying excited electronic states. Also like the MCN/MNC molecules, the MCCH species have rather large ligand dissociation energies. Due to the prevalence of C_{n}H polyyne molecules discovered in the interstellar medium, members of the MCCH series likely exist as relevant astrochemicals and could be involved in prebiotic reactions.

The physical properties of gas phase metal monoacetylide (MCCH, where M = Sc–Zn) molecules have been evaluated with coupled cluster theory and multireference configuration interaction. Some of the MCCH molecules share a trait with their isoelectronic metal monocyanide counterparts: profound multireference character and low-lying excited electronic states. Members of the MCCH series likely exist as relevant astrochemicals and could be involved in prebiotic reactions.

Models of the Fischer–Tropsch reaction typically focus on two proposed mechanisms for the initial carbon monoxide dissociation: unassisted dissociation (carbide mechanism), and hydrogen-assisted dissociation via an adsorbed oxymethylidene (HCO*) intermediate. Much evidence for hydrogen-assisted dissociation comes from density functional theory calculations modeling ruthenium nanoparticle catalysts as infinite, periodic metal slabs. However, the generalized gradient approximations (GGAs) used in these calculations can make significant errors in reaction barrier heights. How these errors affect the predicted selectivity to unassisted vs. hydrogen-assisted dissociation is not well understood. We address the problem by considering a different regime, applying GGA and beyond-GGA approximations to CO dissociation on a “magic” nonmagnetic Ru_{12} cluster modeling supported nanoparticle catalysts. Both approximations concur that hydrogen-assisted dissociation is facile on this cluster, providing additional support for its potential role in real catalysts.

Understanding the surface interactions between involved in heterogenous catalysis is of vital importance to the development and optimization of catalytic materials. This article reviews challenges in the cluster model for surface interactions and examines the role of hydrogen in CO dissociation using multiple density functional theory approximations.

In this work, we present an overview on how density functional theory calculations can be used to design novel electrocatalytic materials for fuel cells. In particular, we focus the attention on non-metal doped graphene systems, which were reported to present excellent performances as electrocatalysts for the oxygen reduction reaction (ORR) at the cathodic electrode of fuel cells and are, thus, considered promising substitutes of platinum or platinum alloys electrodes. The methodology, originally proposed by Nørskov et al. (J. Phys. Chem. B 2004, 108, 17886) for electrochemical processes at metal electrodes, is revisited and applied specifically to doped graphene. Finite molecular models of graphene are found to perform as well as periodic models for localized properties or reactions. Therefore, the sophisticated molecular quantum mechanics methodologies can be safely used to compute reliable Gibbs free energies of reaction in an aqueous environment for the various steps of reduction (at the cathode) or of oxidation (at the anode). Details of the reaction mechanisms and accurate cell onset- or over-potentials can be derived from the Gibbs free energy diagrams. The latter are computational quantities which can be directly compared to experimentally obtained cell overpotentials. Modeling electrocatalysis at fuel cells is, thus, an extremely powerful and convenient tool to improve our understanding of how fuel cells work and to design novel potentially active electrocatalytic materials. In this work, we present two specific applications of B-doped graphene, as electrocatalysts for the ORR at a half-cell cathode and for the methanol oxidation reaction (MOR) at a half-cell anode.

Non-metal doped graphene has great potential to replace platinum as electrode material in energy-related devices. Quantum chemical simulation of a prototypical fuel cell is a powerful tool to understand the electrochemical processes at the cathode (oxygen reduction reaction) and at the anode (methanol oxidation reaction) and to design novel and efficient electrocatalytic materials.

The role of Virtual Reality (VR) tools in molecular sciences is analyzed in this contribution through the presentation of the Caffeine software to the quantum chemistry community. Caffeine, developed at Scuola Normale Superiore, is specifically tailored for molecular representation and data visualization with VR systems, such as VR theaters and helmets. Usefulness and advantages that can be gained by exploiting VR are here reported, considering few examples specifically selected to illustrate different level of theory and molecular representation.

The massive evolution of three dimensional interactive computer graphics and Immersive Virtual Reality (IVR) technologies offers nowadays interesting opportunities in molecular representation. This contribution presents a new molecular viewer, called Caffeine, specifically designed to exploit the latest IVR technologies, highlighting its applications in the visualization and analysis of data coming from QM and MM computations.

Binding capabilities of hydrogen molecules on Li doped metal carbide nanotubes (MCNT, M = Si, Ge, Sn) have been compared from *ab initio*-based calculations using quantum mechanical /molecular mechanics methodology. Geometry optimizations are carried out at the ONIOM2 (B3LYP/6-31 + G(d)//LANL2DZ:UFF) level of theory with coronene ring as a model in the high layer. Lithium binding energies on each of the pure armchair (5,5) and zigzag (6,0) MCNTs are calculated. Adsorptions of one and two H_{2} molecules on the Li doped nanotubes are successively studied. In both cases the complexes are found to be stable and the average adsorption energy falls in between −18 and −38 kcal/mol. Stabilities of Li@MCNT, H_{2}/Li@MCNT, and (H_{2})_{2}/Li@MCNT systems are confirmed from the HOMO-LUMO gap and three chemical reactivity descriptors such as chemical potential, hardness and electrophilicity index. The charge polarization mechanism plays a pivotal role in the H_{2} adsorption on the surface of Li@MCNT. The dispersion corrected M06-2X functional is also included in the calculation to investigate the changes in the H_{2} binding properties. The interaction of H_{2} with the lithium doped MCNT has also been analyzed from the total electron density maps and density of states projected to different atoms.

Hydrogen has the potential to replace fossil fuel and changing the current energy landscape. However, its use is not practical until technology that allows storing hydrogen in a way that it can be easily retrieved, as and when necessary, is established. Several pristine or doped nanotubes can act as hydrogen storage materials. The H_{2} storage capabilities of lithium doped nanotubes of silicon, germanium, and tin carbides can be studied by means of quantum mechanical /molecular mechanics calculations.

The theoretical modeling of chemical reactions in condensed phase still represents an open field of investigation for theoretical–computational chemistry. In this context, we have proposed a methodology (the Perturbed Matrix Method [PMM]), based on the first principles of statistical mechanics and on the use of molecular simulations, which has demonstrated its ability in quantitatively predicting the kinetics and the thermodynamics of chemical reactions in complex atomistic environments. In this study, we demonstrate the features of PMM by modeling the resonant Electron Transfer bimolecular reaction between ferrocene and ferrocenium in solution. The obtained results, despite the adopted approximations and the intrinsic limitations of the approach, are in very good agreement with the experimental data and demonstrate the ability of the method for addressing complex reactions in solution and for evaluating the kinetics of slow events out of the potentialities of the state-of-the-art molecular simulations.

A theoretical–computational approach, based on molecular dynamics simulations and Perturbed Matrix Method, is proposed for modeling bimolecular electron transfer reactions in condensed phase. The resonant electron transfer bimolecular reaction between ferrocene and ferrocenium ion in acetonitrile solution is utilized as case study. The agreement with the experimental data demonstrates good performance of the proposed theoretical–computational procedure despite several approximations and drawbacks commented in the study.

In this tutorial review, we present some effective methodologies available for the simulation of vibrational and vibrationally resolved electronic spectra of medium-to-large molecules. They have been integrated into a unified platform and extended to support a wide range of spectroscopies. The resulting tool is particularly useful in assisting the extensive characterization of molecules, often achieved by combining multiple types of measurements. A correct assessment of the reliability of theoretical calculations is a necessary prelude to the interpretation of their results. For this reason, the key concepts of the underlying theories will be first presented and then illustrated through the study of thiophene and its smallest oligomer, bithiophene. While doing so, a complete computational protocol will be detailed, with emphasis on the strengths and potential shortcomings of the models employed here. Guidelines are also provided for performing similar studies on different molecular systems, with comments on the more common pitfalls and ways to overcome them. Finally, extensions to other cases, like chiral spectroscopies or mixtures, are also discussed.

Cost-effective methodologies to simulate and interpret accurate vibrational and electronic spectra, directly comparable to experiment, are described from a theoretical and practical perspectives. Key aspects regarding their application on real cases are discussed through the design of a complete computational protocol starting from the definition of the best suited electronic structure calculation method, using thiophene and bithiophene as test cases. Possible shortcomings and strategies to overcome the limitations of those methods are also presented.

Molecular structure is one of the most relevant concepts in chemistry. It plays a central role in determining molecular and spectroscopic properties: a mandatory prerequisite for a thorough understanding of the chemical and physical properties of molecules is in fact represented by the knowledge of their geometrical structures. While in some fields a qualitative description of the molecular structure might be sufficient, in many others, like for example spectroscopy, a quantitative, and accurate determination is mandatory. Nowadays, the most advanced computational methodologies allow reliable structural predictions able to fulfil the proper accuracy requirements. This contribution provides an overview on this topic, focusing on the computational strategies that permit accurate equilibrium structure determinations for systems ranging from small molecules to medium-sized building-blocks of biomolecules.

The development of computational strategies that permit accurate equilibrium structure determinations for systems ranging from small molecules to medium-sized biosystems is one of the main challenges in theoretical chemistry. Composite approaches have been developed in order to account for both electron correlation and basis-set effects at the best possible level. The additivity approximation is at the heart of these approaches: the various contributions are evaluated separately at the highest possible level and then combined together.

Solvent effects on chiroptical properties and spectroscopies can be huge, and affect not only the absolute value but the sign of molecular chiroptical responses. Therefore, the definition of reliable theoretical models and computational protocols to calculate chiroptical responses and assist the assignment of the chiral absolute configuration cannot overlook the effects of the surrounding environment. Continuum solvation methodologies are successful in case of weakly interacting solute–solvent couples, whereas in case of strongly interacting systems, such as those dominated by explicit hydrogen bonding interaction, a change of strategy is required to gain a reliable modeling. In this review, a recently developed integrated Quantum-Mechanical/Polarizable molecular mechanics (MM)/polarizable continuum model (PCM) method is discussed, which combines a fluctuating charge approach to the MM polarization with the PCM. Its theoretical fundamentals, and issues related to the calculation of chiroptical responses are summarized, and the application to few representative test cases in aqueous solution is discussed.

Solvent effects have great influence on chiroptical properties of molecular systems, and therefore cannot be ignored in theoretical models. Recently developed, integrated QM/polarizable MM/Continuum strategies based on fluctuating charges have demonstrated to be powerful approaches to quantitatively reproduce chiroptical properties and spectroscopies of aqueous solutions dominated by specific hydrogen-bonding effects.

Computational modeling methods play a prominent role in the field of homogeneous catalysis given that reaction cycles tend to be multistep complicated processes, where the active catalytic species or intermediates are challenging or impractical to study via experimental approaches. At the same time, as such processes are purely molecular, modeling is viable even if very often computationally costly. The possibility to equally well access stable experimentally observable catalytic intermediates and short-life inaccessible species, such as high energy intermediates and, especially, transition states allows exploring and unraveling complete reaction mechanisms. The quantum mechanical description of intricate catalytic cycles is discussed here for three homogeneous catalytic systems all focused on the use of hydrogen as a potential zero-emission energy carrier for the future.

Computational modeling methods play a prominent role in the field of homogeneous catalysis given that reaction cycles tend to be multistep complicated processes, where the active catalytic species or intermediates are challenging or impractical to study via experimental approaches. The quantum mechanical description of intricate catalytic cycles is discussed here for three homogeneous catalytic systems all focused on the use of hydrogen as a potential zero-emission energy carrier for the future.

π-Conjugated small molecules containing diketopyrrolopyrrole (DPP) and thiophene moieties represent a modern class of functional materials that exhibit promising charge transport properties and therefore have great potential as building blocks of active elements of electronic devices. As a starting point of this computational study, the molecular structure, electronic characteristics, and reorganization energies associated with electron or hole transfer are considered. Prediction of molecular crystal packing is followed by the calculation of couplings between adjacent molecules and detection of the effective charge transfer pathways. Finally, the rates of charge transfer process are evaluated. The obtained results shed light not only on the properties of materials containing low-molecular species but also serve as a benchmark for further classical force-field simulations of DPP-based polymers.

π-Conjugated small molecules containing diketopyrrolopyrrole and thiophene moieties represent a modern class of functional materials that exhibit promising charge transport properties and therefore have great potential as building blocks of active elements of electronic devices. A combination of density functional theory, molecular mechanics and Monte Carlo simulations provides new insight in the molecular structure, electronic and transport properties, crystal packing of two conformers of DPP-based system symmetrically disubstituted with bithiophenes.

Structural characteristics of model monolayers of dilauroyl phosphatidylcholine (1,2-dilauroyl-sn-glycerol-3-phosphatidylcholine [DLPC]) adsorbed at the water/vapors and water/octane interfaces were studied by means of computational chemistry methods. Coarse-grained, followed by all-atom molecular dynamics simulations were used to obtain the monolayers equilibrium structures at room temperature at both fluid interfaces. The analysis of the polar head orientation, polar region thickness, tail lengths, and NMR order parameter revealed that the different interface composition affects only the tail lengths and their orientation with respect to the interface. At the octane/water boundary the DLPC tails are less extended than the tails at the water/vacuum interface and are rather significantly tilted or multiply folded. Very similar structuring of the polar DLPC region at both studied boundaries was established. Dynamic ^{13}C NMR chemical shift values, *δ*(^{13}C) computed with density functional theory allowed to identify the interface effect on the DLPC molecular structure and the intramolecular motions in the adsorbed monolayer at the room temperature equilibrium. Detailed analysis of these dynamic *δ*(^{13}C) values compared with available experimental data and static *δ*(^{13}C) estimates of one DLPC low-energy conformer are presented and discussed.

Phospholipids are amphiphilic molecules, which can be obtained from natural products (egg yolk, soybeans, etc.). At the oil/water interface, they are known to act as very good stabilizers of emulsion structures. NMR deuterium order parameter and dynamically averaged ^{13}C NMR chemical shifts are used to relate the intermolecular structuring of a model lipid monolayer at water/vapors and water/oil interfaces with the intramolecular bonds and angles fluctuations.

Elementary processes involving atomic and molecular species at surfaces are reviewed. The emphasis is on simple classical and quantum models that help to single out unifying dynamical themes and to identify the basic physical mechanisms that underlie the rich variety of phenomena of surface chemistry. Starting from an elementary description of the energy transfer between a gas-phase species and a surface—for both classical and quantum lattices—the key processes establishing the formation of an adsorbed phase (sticking, diffusion and vibrational relaxation) are discussed. This is instrumental for introducing the simplest chemical transformations involving adsorbed species and/or scattering of gas-phase molecules: Langmuir–Hinshelwood, Hot-Atom, and Eley–Rideal reactions forming complex molecules from elementary constituents, and dissociative chemisorption of molecules into smaller fragments. Applications are also provided illustrating the ideas developed along the way at work in real-world gas-surface problems.

Simple classical and quantum analytical models provide valuable insight into elementary dynamical processes occurring at the gas-surface interface. In particular, information can be obtained from calculations on energy transfer processes that determine the establishment of an adsorbed phase on the surface, as well as the efficiency and the energy partitioning of most gas-surface reactions.

Density functional theory and *ab initio* calculations were performed to elucidate the hydrogen interactions in (H_{2}O_{4})_{n} (*n* = 1–4) clusters. The optimized geometries, binding energies, and harmonic vibrational frequencies were predicted at various levels of theory. The trans conformer of the H_{2}O_{4} monomer was predicted to be the most stable structure at the CCSD(T)/aug-cc-pVTZ level of theory. The binding energies per H_{2}O_{4} monomer increased in absolute value by 9.0, 10.1, and 11.8 kcal/mol from *n* = 2 to *n* = 4 at the MP2/cc-pVTZ level of theory (after the zero-point vibrational energy and basis set superposition error corrections). This result implies that the intermolecular hydrogen bonds were stronger in the long-chain clusters, that is, the formation of the longer chain in the (H_{2}O_{4})_{n} clusters was more energetically favorable.

H_{2}O_{4} (as the HOO radical dimer) has been proposed as an important intermediate in the formation of H_{2}O_{2} and molecular oxygen from the HOO radical. The concentration of (H_{2}O_{4})_{n} clusters under typical atmospheric conditions should be very low. Theoretical results suggest that the formation of the longer chain in the (H_{2}O_{4})_{n} clusters is more energetically favorable. This result implies that the thermodynamic stability increased for larger values of *n* in the H_{2}O_{n} dimers.

The heavy atom (HA) effect on the NMR isotropic carbon shielding constants is computationally investigated in the series of model ethanes, ethylenes, and acetylenes, C_{β}H_{3}—C_{α}H_{2}—XH_{n}, C_{β}H_{2}—C_{α}H—XH_{n}_{,} C_{β}H≡C_{α}—XH_{n} (*n* = 0, 1, 2, or 3 depending on X), where X covers p-elements in the 13–17 groups of the 3–6 periods in as many as 60 compounds. Compounds under study provide diverse bonding situations for the α- and β-carbons, which are characterized by the consecutive increase of the s-character of the C_{β}—C_{α} and C_{α}—X bonds, being one of the factors influencing spin-orbit part of the HA on light atom effect (SO-HALA). The “chalcogen dependence,” “pnictogen dependence,” “tetrel dependence,” and “triel dependence” are established for the 16th, 15th, 14th, and 13th groups, respectively. A well-known “normal halogen dependence” for the ^{13}C NMR chemical shifts, established much earlier for the compounds containing 17th group elements, also revealed itself in all three series under investigation. The dependence of the spin-orbit effects size depending on the number of the lone electron pairs (LEPs) on HA X has also been investigated. The comparison of theoretical ^{13}C NMR chemical shifts with experiment is performed for three representative tellurides. The HALA effect in this series has been shown to be strongly dependent on the number of tellurium LEPs.

Accurate, first-principles nonrelativistic modeling is a versatile tool for the prediction of ^{13}C NMR spectra. Shielding constants are highly sensitive to the presence of heavy atoms, due to the manifestation of the so-called HALA effect. This effect is computationally investigated in a series of model compounds, C_{β}H_{3}—C_{α}H_{2}—XH_{n}, C_{β}H_{2}C_{α}H—XH_{n}_{,} C_{β}H≡C_{α}—XH_{n} (*n* = 0, 1, 2, or 3 depending on X), where X covers p-elements of the 13–17 groups of the 3–6 periods of the Periodic Table.

In this work, the position and momentum space information densities of the Eckart potential are graphically demonstrated and their properties are studied. The position space information densities have quite an asymmetric shape depending on the values of quantum numbers. The information entropy is obtained and Bialynicki-Birula and Mycielski inequality is numerically saturated for some parameters of the potential. It is shown that the inequality is saturated with increasing potential depth.

Quantum information theory forms the framework for proper understanding of quantum communication and quantum computation. It measures the amount of information present in a system. The information entropy of one of the important exponential type-Eckart potential is studied. The Fourier transform of this system would be interesting in different fields. The information density of the Eckart potential is graphically demonstrated and the Bialynicki-Birula and Mycielski inequality is attempted to saturate.

We introduced an efficient initial guess method, namely the grid-cutting, which is specialized for grid-based density functional theory (DFT) calculations. It produces initial density and orbitals through pre-DFT calculations in an inner simulation box made by cutting out the outer region of a full-size one. To assess its performance, we carried out DFT calculations for small molecules included in the G2-1 set and two large molecules with various combinations of mixing and diagonalization conditions, relative size of the inner box, and grid spacing. For all cases, the grid-cutting method was more efficient than conventional ones such as extended Hückel, superposition of atomic densities, and linear combination of atomic orbitals. For instance, it was about 20% faster in computational time and about 45% smaller in the number of self-consistent-field cycles than the superposition of atomic densities because it provided high-quality initial density and orbitals closer to the corresponding fully converged values. In addition, it showed good performance for non-Coulombic model systems such as harmonic oscillator.

A novel, efficient initial guess method shows better performance than conventional methods in grid-based density functional calculations. This approach is able to provide high-quality initial density and orbitals by performing pre-DFT calculations in a simulation box obtained by eliminating the outer region of the full model. This method is also effective for non-Coulombic model systems, such as the harmonic oscillator and quantum wells.

P218 is one of the very important and recent lead compounds for antimalarial research. The 3D structural and electronic details of P218 are not available. In this article, quantum chemical studies to understand the possible 3D structures of P218 are reported and compared with 3D structures from the active site cavities of *h*DHFR and *Pf*DHFR. The neutral P218, can adopt open chain as well as cyclic arrangements. Under implicit solvent condition a zwitterionic-cyclic conformer is found to be quite possible. Microsolvation studies using explicit water molecules indicate that one water molecule may bridge the two ends of zwitterionic-cyclic P218. It was observed that the protonation occurs preferentially at N^{1} position of the 2,4-diaminopyrimidine ring, with a proton affinity of 274.49 kcal/mol (implicit solvent phase) and 236.35 kcal/mol (gas phase). A dimer of P218 may be zwitterionic dimer, the dimer formation can release upto ∼28.60 kcal/mol (implicit solvent phase).

Quantum chemical methods are employed to study the 3D structure and electronic structure of an important antimalarial lead compound P218. Solvation conditions affect P218's structure and charged state. The system is found to be stable as a zwitterionic dimer in polar media. Protonated P218 is characterized by charge localized N^{3} center which may be a divalent N(I) center.

The use of variational nuclear motion programs to compute line lists of transition frequencies and intensities is now a standard procedure. The ExoMol project has used this technique to generate line lists for studies of hot bodies such as the atmospheres of exoplanets and cool stars. The resulting line list can be huge: many contain 10 billion or more transitions. This software update considers changes made to our programs during the course of the project to allow for such calculations. This update considers three programs: Duo which computed vibronic spectra for diatomics, DVR3D which computes rotation-vibration spectra for triatomics, and TROVE which computes rotation-vibration spectra for general polyatomic systems. Important updates in functionality include the calculation of quasibound (resonance) states and Landé g-factors by Duo and the calculation of resonance states by DVR3D. Significant algorithmic improvements are reported for both DVR3D and TROVE. All three programs are publically available from ccpforge.cse.rl.ac.uk. Future developments are also considered.

Molecular spectra provide important remote sensing fingerprints. However, hot molecules can undergoing very large numbers of possible transitions: billions for even fairly small molecules such as methane. Nuclear motion software based on the use of the variational principle used to compute line lists is discussed and the adaptation of the programs to the demands of computing huge lists of molecular transitions described.

The water exchange reactions in aquated Li^{+} and Be^{2+} ions were investigated with density functional theory calculations performed using the [Li(H_{2}O)_{4}]^{+}·14H_{2}O and [Be(H_{2}O)_{4}]^{2+}·8H_{2}O systems and a cluster-continuum approach. A range of commonly used functionals predict water exchange rates several orders of magnitude lower than the experimental ones. This effect is attributed to the overstabilization of coordination number four by these functionals with respect to the five-coordinated transition states responsible for the associative (**A**) or associative interchange (**I _{a}**) water exchange mechanisms. However, the M06 and M062X functionals provide results in good agreement with the experimental data: M062X/TZVP calculations yield a concerted

DFT calculations provided using cluster-continuum models provide a detailed picture of the water exchange mechanism in [Be(H_{2}O)_{4}]^{2+} and [Li(H_{2}O)_{4}]^{2+} at the molecular level and activation parameters in excellent agreement with experimental data.

A unified, computer algebra system-based scheme of code-generation for computational quantum-chemistry programs is presented. Generation of electron-repulsion integrals and their derivatives as well as exchange-correlation potential and its derivatives is discussed. Application to general-purpose computing on graphics processing units is considered.

The complexity of computational kernels in quantum-chemical calculation calls for methods of describing the formulas and algorithms in a high-level, easy to understand and maintain way that can be easily implemented to take advantage of performance offered by different architecture. Automatic code generation techniques are introduced for some of the most challenging implementation tasks present in typical quantum-chemical software, electron-repulsion integrals, their gradients, as well as exchange-correlation functionals and their derivatives.

We present an *efficient* quantum algorithm for beyond-Born–Oppenheimer molecular energy computations. Our approach combines the quantum full configuration interaction method with the nuclear orbital plus molecular orbital method. We give the details of the algorithm and demonstrate its performance by classical simulations. Two isotopomers of the hydrogen molecule (H_{2}, HT) were chosen as representative examples and calculations of the lowest rotationless vibrational transition energies were simulated. © 2016 Wiley Periodicals, Inc.

While the best known classical algorithm for full configuration interaction scales exponentially, algorithms for a quantum computer provide polynomial scaling (i.e. are efficient). This also allows for efficient beyond-Born-Oppenheimer full configuration interaction calculations. Two isotopomers of the hydrogen molecule (H2, HT) were chosen as representative examples and calculations of the lowest rotationless vibrational transition energies were simulated.

Although previously studied [(HOOC)_{4}(TBPor)Ru(NCS)_{2}]^{2–} (**A**; TBPor = tetrabenzoporphrin) avoided the intrinsic π-stacking aggregation of planar metallophorphryins via incorporating two axial ligands, these isothiocyanato groups are believed to be the weakest part of the sensitizer while operating in dye-sensitized solar cells (DSSCs). In this work, a series of thiocyanate-free ruthenium porphyrin complexes featuring with phenyl/substituted-phenyl axial groups, [(HOOC)_{4}(TBPor)Ru(L′)_{2}]^{2–} (L′ = Ph (**1**), PhF_{2} (**2**), PhCl_{2} (**3**), PhBr_{2} (**4**), and PhI_{2} (**5**)), have been examined using density functional theory (DFT) and time-dependent DFT (TD-DFT). Both analyses of electronic structures and calculations of interaction energies demonstrate that the Ru-L′ interaction in **1**–**5** is significantly enhanced relative to the Ru-NCS in **A**, which will raise chemical stability of the former in DSSCs. Single-electron oxidation mechanism has been proposed. Oxidation potentials (*E*^{0}) are increased by 0.2–0.6 V when changing axial groups from NCS to Ph/PhX_{2}. The spin-orbit coupling (SOC) relativistic effects can be negligible in computing *E*^{0} values. TD-DFT calculations show that **1**–**5** have more intense *Q* band in the visible region than **A** does. Taken together, high chemical stability, suitable oxidation potential and expanding absorption spectra would allow for potential applications of the thiocyanate-free sensitizers in DSSCs. © 2016 Wiley Periodicals, Inc.

Ruthenium porphyrin complexes with phenyl axial groups, replacing isothiocyanato donors, were examined using DFT/TD-DFT approach, which show stronger interaction between Ru and axial groups, more positive oxidation potentials and more intense *Q* absorption bands. The newly designed sensitizers are anticipated to be promising in dye-sensitized solar cells.

We describe the implementation and application of a recently developed time-dependent density-functional theory (TDDFT) algorithm based on the complex dynamical polarizability to calculate the photoabsorption spectrum of large metal clusters, with specific attention to the field of molecular plasmonics. The linear response TDDFT equations are solved in the space of the density fitting functions, so the problem is recast as an inhomogeneous system of linear equations whose resolution needs a numerical effort comparable to that of a SCF procedure. The construction of the matrix representation of the dielectric susceptibility is very efficient and is based on the discretization of the excitation energy, so such matrix is easily obtained at each photon energy value as a linear combination of constant matrix and energy-dependent coefficients. The code is interfaced to the Amsterdam Density Functional (ADF) program and is fully parallelized with standard message passing interface. Finally, an illustrative application of the method to the photoabsorption of the Au_{144}(SH)_{60} cluster is presented. © 2016 Wiley Periodicals, Inc.

Efficient and accurate prediction of photoabsorption spectra for large systems is a fundamental goal of modern computational research. This is usually achieved within the time-dependent density-functional theory (TDDFT) approach but high associated computational costs limit its applicability to large systems. A recently developed TDDFT algorithm based on the complex dynamical polarizability to calculate the optical photoabsorption of large metal clusters is particularly suitable for applications in the field of plasmonics.

Based on the Kohn–Sham Pauli potential and the Kohn–Sham electron density, the upper bound of the Pauli kinetic energy is tested as a suitable replacement for the exact Pauli kinetic energy for application in orbital-free density functional calculations. It is found that bond lengths for strong and moderately bound systems can be qualitatively predicted, but with a systematic shift toward larger bond distances with a relative error of 6% up to 30%. Angular dependence of the energy-surface cannot be modeled with the proposed functional. Therefore, the upper bound model is the first parameter-free functional expression for the kinetic energy that is able to qualitatively reproduce binding curves with respect to bond distortions. © 2016 Wiley Periodicals, Inc.

Orbital-free calculations have gained much interest over recent years as they promise a reliable physical description of the system at low computational cost. In this study the upper bound of the Pauli kinetic energy is tested as a suitable replacement for the exact Pauli kinetic energy for application in orbital-free calculations.

We present *ab initio* calculations of the electron density properties and metallophilic interactions of the gold halide series, AuX_{2} and Au_{2}X (X = F–I) as well as their anions performed at MP2 theoretical level with extended basis sets. The gold halide's structure, stability, and interactions with alkali metal atoms were investigated. The mechanisms of metallophilic interactions were explored by natural bond orbital analyses, electron localization function, electron density deformation, atoms in molecules, and reduced density gradient analyses. © 2016 Wiley Periodicals, Inc.

“Superhalogens” are clusters consisting of a metal atom surrounded by electronegative atoms that display extremely high electronic affinity. The nature of the Gold-halogen interaction in Gold-containing superhalogens is investigated from first-principles. The overlap of spd hybrid orbitals in gold and sp hybrid orbitals in the halogen dominate the metallophilic interaction. The contributions of the halogen increase from the lighter F to heavier I, with increasingly covalent bond character.

The geometric and electronic structures of a series of silicon fluorides
(*n* = 4 − 6) were computationally studied with the aid of density functional theory (DFT) method with B3LYP and M06-2X functionals and coupled cluster (CCSD and CCSD(T)) methods with 6-311++G(d,p) basis set. The nature of the Si-F bonds in these compounds was analyzed in the framework of the natural bond orbital theory and natural resonance theory. Energy characteristics (heats of reactions and energy barriers) of the dissociation reactions
SiF_{4} + F^{–} and
+ F^{–} were calculated using the DFT and CCSD methods. The potential energy surface of elimination of a fluoride anion from
has a specific topology with valley-ridge inflection points corresponding to bifurcations of the minimal energy reaction path. © 2016 Wiley Periodicals, Inc.

The series of compounds
(*n* = 4–6) and the reactions of elimination of the fluoride anion from
and
are studied by density functional theory and *ab initio* methods. A well-defined ionic nature, of the single two-center, two-electron (2c-2e) type, is characteristic for the bonds in all species. In the case of the trigonal bipyramidal
anion, this finding is in contrasts with the traditional definition of axial SiF bonds.

In this review, the origins of astrochemistry and the initial applications of quantum chemistry to the discovery of new molecules in space are discussed. Furthermore, more recent successes and failures of quantum astrochemistry are explored. Finally, the application of quantum chemistry to the chemical study of space is driving developments in large-scale computational science. Consequently, cloud computing and large molecule computations are discussed. Astrochemistry is a natural application of quantum chemistry. The ability to analyze routinely and completely the structural, spectroscopic, and electronic properties of any given molecule, regardless of its laboratory stability, make this tool a necessary component for astrochemical analysis. The sizes of the computations scaling with the number of electrons and degrees-of-freedom can become limiting, but proper choices of methods can provide unique insights. The chemistry of the Earth is a small snapshot of the chemistries available in the universe at large, and the flexibility inherent within computation make quantum chemistry an excellent driver of new knowledge in fundamental molecular science as well as in astrophysics. © 2016 Wiley Periodicals, Inc.

Quantum chemistry has long been a necessary tool in the elucidation of astronomical spectroscopy. This review highlights the past, present, and future of what quantum chemistry has to offer the astrochemist.

Sr_{2}Fe_{1.5}Mo_{0.5}O_{6−δ} (SFMO) is a promising electrode material for solid oxide electrochemical cells. This perspective highlights the role of first-principles investigations in unveiling SFMO structural, electronic, and defect properties. In particular, DFT + U provides a reliable and convenient tool for extensive studies on strongly correlated transition-metal oxides, as SFMO and related systems. The SFMO excellent performances are ascribed to a mixed oxide ion-electron conductor character. Crucial features are the easy formation of oxygen vacancies and the low oxide migration barrier heights. Aliovalent doping with K^{+} enables convenient hydration and effective proton transport in bulk SFMO. This opens a route toward new promising triple-conductor oxides. Besides discussion of specific SFMO applications, our results help to uncover general perovskite-oxide features and new design principles for oxide- and proton-conducting solid oxide fuel cell electrodes. © 2016 Wiley Periodicals, Inc.

Quantum-chemical investigations can boost the development of advanced materials for energy conversion technologies. In the context of solid oxide fuel cells, the case of Sr_{2}Fe_{1.5}Mo_{0.5}O_{6−δ}-based electrodes exemplifies the successful application of DFT methods to the rational design of triple-conductor oxides, highlighting the key structure–property–function relationships that determine the oxide and proton bulk transport processes in perovskite oxides.

Solid-state NMR spectroscopy and computational approaches such as Molecular Dynamics (MD) simulations and Density Functional Theory have proven to be very useful and versatile techniques for studying the structure and the dynamics of noncrystalline materials if a direct comparison between experiment and theory is established. In this review, the basic concepts in first-principle modeling of solid-state NMR spectra of oxide glasses are presented. There are three theoretical ingredients in the computational recipe. First, classical or *ab initio* molecular dynamics simulations are employed to generate the structural models of the glasses of interest. Second, periodic Density Functional Theory calculations coupled with the gauge including projector augmented-wave (GIPAW) algorithm form the basis for the *ab initio* calculations of NMR parameters (chemical shielding and quadrupolar parameters). Finally, Spin-effective Hamiltonian are employed to simulate the solid-state NMR spectra directly comparable with the experimental counterparts. As an example of this methodology, the investigation of the local and medium range structure of Na-Ca silicate and aluminosilicate glasses that are usually employed as simplified models for basaltic, andesitic and rhyolitic magmas will be reported. We will show how the direct comparison of the theoretical NMR spectra of MD derived structural models with the experimental counterparts allows gaining new insights into the atomistic structure of very complex oxide glasses. © 2016 Wiley Periodicals, Inc.

Molecular dynamics simulations coupled with DFT-GIPAW NMR calculations and spin-effective Hamiltonians provide a clear view of the local and medium range structure of multicomponent alumina silicate glasses.

On page 1274 Yi Luo and co-workers examine the regioselective polymerization of 1,3-dienes catalyzed by a bipyridine-ligated iron(II) complex using DFT. Steric effects were found to play an important role in regioselectivity. The catalytically active species is found to be at the open-shell quintuplet ground state with no spin distribution on the redox-active bipyridiene ligand. (DOI: 10.1002/qua.25167)

The regioselective polymerizations of isoprene and 3-methyl-pentadiene catalyzed by a cationic iron (II) complex bearing bipyridine ligand have been computationally studied. Having achieved an agreement between calculation and experiment, it is found that the open-shell unpaired 3d-electrons localize on Fe center rather than partially distribute on the redox-active bipyridine ligand. The steric effect plays a more important role in controlling the regioselectivity in comparison with electronic factors. The deformation energy is mainly contributed by monomer and Fe-alkyl moieties rather than the bipyridine ligands themselves, although noncyclopentadienyl ancillary ligands are often deformed in most insertion transition states for selective polymerization of olefin. © 2016 Wiley Periodicals, Inc.

DFT calculations indicate that steric effect plays an important role in the regioselectivity in the polymerizations of dienes catalyzed by a cationic bipyridine-ligated iron(II) complex. The catalytically active species is found to be at the open-shell quintuplet ground state with no spin distribution on the redox-active bipyridiene ligand.

We report the results of a DFT study of the electronic properties, intended as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, of periodic models of H-passivated *armchair* graphene nanoribbons (*a*-GNRs) as that synthetized by bottom-up technique, functionalized by vicinal dialdehydic groups. This material can be obtained by border oxidation in mild and easy to control conditions with ^{1}*Δ _{g}* O

Tuning the energies of frontier orbitals of graphene nanoribbons (GNRs) is important because the HOMO-LUMO gap affects the electronic and optic properties of such materials, and as such their applicability for electronic devices. First-principles calculations suggest that frontier orbital energies of armchair GNRs can be tuned through dialdehydic functionalization by oxidation in mild conditions.

According to Koopmans theorem, the derivative of the energy of a canonical molecular orbital (MO) with respect to nuclear coordinates quantifies its bonding/antibonding character. This quantity allows predictions of bond length variation on ionisation in a panel of 19 diatomic species. In polyatomic molecules, the derivative of a MO energy with respect to a given bond length reveals the nature and the degree of the bonding/antibonding contribution of this MO with respect to this bond. Accordingly, the HOMO “lone pairs” of CO and CN^{−} and the HOMO-2 of CH_{3}CN are found to be antibonding with respect to the CX bond (X = N, O), whereas the HOMO of N_{2} is found to be bonding. With the same approach, the variation of the bonding character in the MOs of CO and CH_{3}CN on interaction with an electron acceptor (modeled through the approach of a proton) or by applying an electric field was studied. © 2016 Wiley Periodicals, Inc.

Molecular orbital energy derivatives with respect to a given bond length provides a simple criterion of bonding/antibonding character of the orbital with respect to this bond in diatomic and polyatomic molecules. For example, the HOMO lone pair of CO and the HOMO-2 one of CH_{3}CN are found antibonding, whereas the HOMO of N_{2} is found bonding. This method appears as a useful tool to rationalize the effects of donor–acceptor interactions.

The structures and nonlinear optical properties of a novel class of alkali metals doped electrides B_{12}N_{12}–M (M = Li, Na, K) were investigated by *ab initio* quantum chemistry method. The doping of alkali atoms was found to narrow the energy gap values of B_{12}N_{12} in the range 3.96–6.70 eV. Furthermore, these alkali metals doped compounds with diffuse excess electron exhibited significantly large first hyperpolarizabilities (*β*_{0}) as follows: 5571–9157 au for B_{12}N_{12}–Li, 1537–18,889 au for B_{12}N_{12}–Na, and 2803–11,396 au for B_{12}N_{12}–K. Clearly, doping of the alkali atoms could dramatically increase the *β*_{0} value of B_{12}N_{12} (*β*_{0} = 0). Furthermore, their transition energies (Δ*E*) were also calculated. The results showed that these compounds had low Δ*E* values in the range 1.407–2.363 eV, which was attributed to large *β*_{0} values of alkali metals doped B_{12}N_{12} nanocage. © 2016 Wiley Periodicals, Inc.

Alkali-doped Boron nitride fullerene-like nanostructures are studied for their nonlinear optical properties. First-principles calculations reveal that doped alkali atoms into pure B_{12}N_{12} can decrease the wide energy gap between HOMO and LUMO in these systems. These alkali metals doped compounds have significantly large first hyperpolarizabilities because of the introduction of the loosely bound excess electrons by the dopant atom.

Simplified Box Orbitals (SBO) are a kind of spatially restricted basis functions. SBOs have a similar use and value to Slater functions but, because they fulfill a version of the zero-differential overlap approximation, they allow for a drastic reduction in the number of two-electron integrals to be calculated when dealing with huge systems, and they seem to be specially adapted to study confined systems such as molecules in solution. In a previous study, the mathematical shape of SBOs was discussed and the necessary parameters were obtained by means of the variational method. In the present study, the parameters of each SBO were obtained by applying the condition that it is as similar as possible to the STO that would be used in a basis set without spatial restrictions. We have developed a method to achieve this likeness and deduced simple formulas to describe all the SBOs of any atom. We also present the SBO-3G expansions of the SBOs obtained, making it possible to use these SBOs with standard quantum chemistry calculation software. Simple formulas were also deduced to directly write the SBOs and SBO-3G corresponding to the atoms with a *Z* value of between 1 and 18. Finally, as a first example of the usefulness of this kind of functions, an optimized SBO-3G basis set is proposed for atoms from H to Cl in molecules. © 2016 Wiley Periodicals, Inc.

Simplified Box Orbitals (SBO) are a kind of spatially restricted basis functions, whose value is zero from a certain distance to the origin, which comply with an updated version of the zero-differential overlap (ZDO) approximation. The use of these functions allows a very important reduction of computation time for HF and DFT calculations, and yield results of equivalent quality to STO basis. They can be managed through Gaussian expansions (SBO-nG), similarly to STO-nG.

Within the framework of density functional theory, a study of approximations to the enhancement factor of the non-interacting kinetic energy functional *T*_{s}[*ρ*] has been presented. For this purpose, the model of Liu and Parr (Liu and Parr, Phys Rev A 1997, 55, 1792) based on a series expansion of *T _{s}*[

The search for an accurate approximation to the functional of the non-interacting kinetic energy (*T*_{s}[*ρ*]) has been an important and long-standing problem in the quantum theory of many-electron systems and DFT. This article shows that the Liu–Parr expansion of this functional gives an adequate description of the kinetic energy enhancement factor and reproduces the shell structure of atoms.