In this article, we examine Hohenberg–Kohn theorems for Current Density Functional Theory, that is, generalizations of the classical Hohenberg–Kohn theorem that includes both electric and magnetic fields. In the Vignale and Rasolt formulation (Vignale and Rasolt, Phys. Rev. Lett. 1987, 59, 2360), which uses the paramagnetic current density, we address the issue of degenerate ground states and prove that the ensemble-representable particle and paramagnetic current density determine the degenerate ground states. For the formulation that uses the total current density, we note that the proof suggested by Diener (Diener, J. Phys.: Condens. Matter. 1991, 3, 9417) is unfortunately not correct. Furthermore, we give a proof that the magnetic field and the ensemble-representable particle density determine the scalar and vector potentials up to a gauge transformation. This generalizes the result of Grayce and Harris (Grayce and Harris, Phys. Rev. A 1994, 50, 3089) to the case of degenerate ground states. We moreover prove the existence of a positive wavefunction that is the ground state of infinitely many different Hamiltonians. © 2014 Wiley Periodicals, Inc.

The Hohenberg–Kohn theorem in the presence of a magnetic field either uses the total current density or the paramagnetic current density. The degenerate ground-state eigenspace is determined by the particle density and the paramagnetic current density. Moreover, using instead the total current density as data, it is proven that the electrostatic potential in a Hamiltonian is determined for a fixed magnetic field.

A double hybrid approximation using the Coulomb-attenuating method (CAM-DH) is derived within range-separated density-functional perturbation theory, in the spirit of a recent work by Cornaton et al. (Phys. Rev. A 2013, 88, 022516). The energy expression recovered through second order is linear in the parameters *α* and *β* that control the Coulomb attenuation. The method has been tested within the local density approximation on a small test set consisting of rare-gas and alkaline-earth-metal dimers as well as diatomics with single, double, and triple bonds. In this context, the semiempirical *α* = 0.19 and *β* = 0.46 parameters, which were optimized for the hybrid CAM-B3LYP functional, do not provide accurate interaction and total energies. Using semilocal functionals with density scaling, which was neglected in this work, may lead to different conclusions. Calibration studies on a larger test set would be necessary at this point. This is left for future work. Finally, we propose as a perspective, an alternative CAM-DH approach that relies on the perturbation expansion of a partially long-range-interacting wavefunction. In this case, the energy is not linear anymore in *α* and *β*. Work is in progress in this direction. © 2014 Wiley Periodicals, Inc.

The use of Coulomb attenuation within hybrid time-dependent density-functional theory (DFT) became popular in recent years in particular for modeling charge transfer excitations. In such an approach, the correlation energy is entirely described with a density functional. Rigorous multideterminantal extensions based on many-body perturbation theory are proposed in this work, to obtain more accurate correlation energies. The resulting Coulomb attenuating double hybrid DFT method gave promising results for rare-gas dimers.

Due to the fact that natural DNA may lack sufficient conductance for direct application in molecular electronics, a novel design of outer-expanded purine analogues was proposed by incorporating an aromatic ring at the N7-C8 site into natural G and A bases from the outside. The effect of the outer-expansion modification on electronic properties of DNA was investigated by density functional theory and molecular dynamics. The analyses revealed that these purine analogues not only preserve the same sizes of natural purine bases, thus avoiding distortions of DNA skeleton induced by the normal ring-inner-expansion modification, but also keep the selectivity of pairing with their natural counterpart C and T bases. More importantly, their electronic properties are enhanced, indicated by the narrowed HOMO–LUMO gaps, the lowered ionization potentials and the improved ultraviolet absorption spectra. This work may provide helpful information for designing of artificial bases as promising building blocks of biomolecular nanowires. © 2014 Wiley Periodicals, Inc.

As natural DNA bases show limitations for direct application in molecular electronics, a novel design of DNA-based nanowires is proposed using outer-expanded purine analogues with aromatic ring at the N7-C8 site into natural G and A bases from the outside. DFT calculations combined with molecular dynamics reveals that these analogues not only preserve the initial sizes of native purine bases but also enhance their electronic properties, thus making them suitable for DNA-based electronics.

Interaction energy (*E*_{int}) values of a variety of hydrogen, halogen, and dihydrogen bonded complexes in the weak, medium, and strong regimes have been computed using W1BD, MP2, M06L density functional theory, and hybrid methods MP4//MP2, MP4//M06L, and CCSD(T)//MP2. W1BD level *E*_{int} and CCSD(T) results reported in the literature show very good agreement (mean absolute deviation = 0.19 kcal/mol). MP2 underestimates *E*_{int} while M06L shows accurate behavior for all except halogen and charge-assisted hydrogen bonds. MP4//MP2, MP4//M06L, and CCSD(T)//MP2 yield *E*_{int} very close to those obtained from W1BD. The high accuracy energy data at MP4/MP2 is used to study the effect of a cation (Li^{+}, NH_{4}^{+}) on the *E*_{int}. The cation enhances electron donation from the donor to noncovalent bonding region leading to substantial enhancement in *E*_{int} (∼141–566% for Li^{+} and ∼105–539% for NH_{4}^{+}) and promotes a noncovalent bond in the weak regime to medium regime and that in the medium regime to strong regime. © 2014 Wiley Periodicals, Inc.

Hybrid methods viz. MP4//MP2, MP4//M06L, and CCSD(T)//MP2 yield accurate binding energies for hydrogen, halogen, and dihydrogen bonded complexes with accuracy close to the more expensive W1BD and CCSD(T) calculations. Monovalent cations exhibit significant enhancing effect on the strength of hydrogen bonds promoting them from weak to medium and from medium to strong regimes.

New adjusted Gaussian basis sets are proposed for first and second rows elements (H, B, C, N, O, F, Si, P, S, and Cl) with the purpose of calculating linear and mainly nonlinear optical (L–NLO) properties for molecules. These basis sets are new generation of Thakkar-DZ basis sets, which were recontracted and augmented with diffuse and polarization extrabasis functions. Atomic energy and polarizability were used as reference data for fitting the basis sets, which were further applied for prediction of L–NLO properties of diatomic, H_{2}, N_{2}, F_{2}, Cl_{2}, BH, BF, BCl, HF, HCl, CO, CS, SiO, PN, and polyatomic, CH_{4}, SiH_{4}, H_{2}O, H_{2}S, NH_{3}, PH_{3}, OCS, NNO, and HCN molecules. The results are satisfactory for all electric properties tested; dipole moment (*µ*), polarizability (*α*), and first hyperpolarizability (*β*), with an affordable computational cost. Three new basis sets are presented and called as NLO-I (ADZP), NLO-II (DZP), and NLO-III (VDZP). The NLO-III is the best choice to predict L–NLO properties of large molecular systems, because it presents a balance between computational cost and accuracy. The average errors for *β* at B3LYP/NLO-III level were of 8% for diatomic molecules and 14% for polyatomic molecules that are within the experimental uncertainty. © 2014 Wiley Periodicals, Inc.

Accurate prediction of electrical properties responsible for nonlinear response is essential to speed up the designing of new molecular building blocks. The paper presents new basis sets constructed for *ab initio* calculation of higher order polarizabilities at affordable cost. These new basis sets (NLO-X) might be applied for large organic molecules.

In this work, we performed density functional calculations to investigate the adsorption and diffusion of hydrogen on Ni-loaded graphene and single layer graphene oxide (SLGO). We evaluated the feasibility of hydrogen spillover in the presence of Ni_{4} cluster and the role of oxygen-containing groups. Our calculations indicate that the hydrogen diffusion is difficult to take place on the Ni/graphene interface due to the stronger NiH bond strength. Further, the chemisorbed H atoms are also hard to diffuse freely on the graphene surface. For the SLGO surface, both hydroxyl and epoxide groups may not facilitate the hydrogen diffusion. Instead, they are readily attracted by the nearby Ni catalyst and hydrogenated to water molecules. © 2014 Wiley Periodicals, Inc.

First principles calculations indicate that hydrogen diffusion on the Ni/graphene interface is difficult due to the stronger NiH bond strength. Furthermore, the chemisorbed H atoms are unlikely to diffuse freely on the graphene surface. On the graphene oxide surface, both hydroxyl and epoxide groups do not facilitate hydrogen diffusion. Instead, they are readily attracted by the nearby Ni catalyst and react with water molecules.

Optimal structures, electronic and thermodynamic properties of the title complexes are presented. The stability of the hydrogen bonded systems is enhanced by the increasing dipole moments whereas in the halogen bonded systems it is also affected by the atom size in the diatomics. The consecutive addition of fluorine atoms to the pyridine moiety results in the decrease of the interaction energy for both types of the investigated bonds. The substitution on the *meta* sites in pyridine leads to more stable complexes than the substitution in the *ortho* position. The role of substitution on electric polarization and electrostatic forces is estimated by the symmetry-adapted perturbation theory energy decomposition. The predicted Gibbs free energies of the complexes of mono fluorinated pyridines with HCl, HF, and ClF are from −12 to −22 kJ mol^{−1} at 200 K. The possible experimental identification of the complexes with respect to the vibrational modes is discussed. © 2014 Wiley Periodicals, Inc.

The varying substitution on the pyridine ring affects the structure of the complexes. Intramolecular and intermolecular vibrational modes might serve for possible experimental identification of the complexes. The possible spontaneous formation at different temperatures is also affected by the substitution as well as on the interaction type between the two molecules. It is shown that some complexes may exist at 200°K, which is a common temperature in the upper troposphere.

The adsorption mode of aromatic molecules on transition metal surfaces plays a key role in their catalytic transformation. In this study, by means of density functional theory calculations, we systematically investigate the adsorption of *p*-chloroaniline on a series of Pd surfaces, including stepped surfaces, flat surfaces, and clusters. The adsorption energies of *p*-chloroaniline on these substrates [Pd(221), Pd(211), Pd(111), Pd(100), Pd_{13}-icosahedral, Pd_{13}-cubo-octahedron, Pd_{55}] are −1.90, −2.13, −1.70, −2.11, −2.53, −2.65, −2.23 eV, respectively. Benzene ring is adsorpted on catalyst rather than amine group in *p*-chloroaniline molecular. A very good linear relationship is further found between the adsorption energies of *p*-chloroaniline and the *d*-band center of both Pd surfaces and clusters. The lower of *d*-band center of Pd models, the stronger adsorption of *p*-chloroaniline on catalysts. In addition, the frontier molecular orbital and density of states analysis explain the adsorption energy sequence: cluster Pd_{13} > stepped Pd(221) surface > flat Pd(111) surface. © 2014 Wiley Periodicals, Inc.

*p*-chloroaniline, one important industrial intermediates for a variety of specific and fine chemicals, can be obtained by hydrogenation of chloronitrobenzene on Pd catalysts. Density functional theory calculations allow to identify a trend in the adsorption energies of *p*-chloroaniline on different Pd catalytic surfaces: cluster > stepped surfaces > flat surface.

Parallel implementations of quantum chemistry programs targeting supercomputers are challenging applications of dynamic load balancing algorithms. The implementation of work stealing (WS) algorithms is discussed and their usefulness is demonstrated. Evaluation of the four-center integrals of a Cu_{10} cluster requires 25 core-hours overall, achieving 88% efficiency with simple WS for 2048 cores, and 97% with task presorting based on a cost estimate. Limitations of cost sorting become noticeable for larger systems. When spatial symmetry is exploited together with integral screening, bundling the original tasks yields an efficiency of 98% for Cu_{79} in O_{h} symmetry on 512, 1204, and 2048 cores. The advantage of WS algorithms described in this work is not limited to the evaluation of four-center integrals. © 2014 Wiley Periodicals, Inc.

Parallel implementations of quantum chemistry programs targeting supercomputers are challenging applications of dynamic load balancing algorithms. An implementation of work stealing (WS) algorithms is discussed and compared to a static backend (ST) for up to 2048 cores. For the evaluation of four-center integrals advantages of task presorting based on a cost estimate (CS) are demonstrated for some systems. The WS implementation is applicable to various numerical algorithms appearing in a quantum chemistry package.

Many chemical reactions involve bond-dissociation. This is also true for reactions at solid surfaces, in which the dissociation step is often limiting but facilitated in comparison to gas-phase reaction channels. This work considers N_{2} dissociation. The molecule is strongly bound and stretched geometries are chosen. Heterogeneous catalysis by copper is simulated. It was investigated in our previous work as it is in many ways a prototype metal presenting a close-packed surface here. These nitrogen molecules are adsorbed on copper and fixed geometries on the dissociation reaction pathway for stretched N_{2} are given using density functional theory (DFT) calculations in a plane-wave basis. This dissociating molecule appears to be underbound using the *ab initio* Perdew, Burke, Ernzerhof (PBE) DFT functional but while this phenomenon accounts for a few percent at 5 Å, at 6 Å, PBE gives less than 30% of the binding energy. This indicates the onset of dissociation. The PBE wave-functions at these bond-lengths serve as trial input for Quantum Monte Carlo (QMC) simulations of the ground states to obtain highly accurate correlated results for the associated activation barriers indicating the catalytic effect on this dissociation. The geometries from this bond-stretching study mimic the transition state (TS). This procedure requires no search for the actual TS geometry. Finite-size effects and fixed-node error are possible limitations to accuracy of this type of QMC study. We are able to limit fixed-node error, using certain trial wave-functions. The finite-size effect is considerable, although comparing two adsorbed geometries cancels about 90% with respect to clean surfaces. Unfolding the cell to simulate a 9 k-point grid (rather than a single k-point) reduces the remainder by at least a factor 130 but relations for calibrating the remaining (2 mHa) error on converged grids are also used. The pseudopotential used to represent the atomic core of copper must also be determined carefully: we leave 11 active electrons but include the 3d shell in the pseudopotential. © 2014 Wiley Periodicals, Inc.

Quantum Monte Carlo (QMC) methods are used to show that stretched N_{2} is significantly under-bound in Density functional estimates. The deficit compared to QMC energies is used to locate a bond-length that behaves like the dissociation transition state. This geometry is adsorbed on Cu(111) and a QMC simulation of the combined system gives an indication of the dissociation barrier and its lowering compared to the gas phase. N radicals are the product of both channels.

Molecular-crystalline duality of graphene ensures a tight alliance of its physical and chemical natures, each of which is unique in its own way. The article examines the physical-chemical harmony and/or confrontation in terms of the molecular theory of graphene. Chemistry that is consistent with graphene physics expectations involves: small mass of carbon atoms, which provides a lightweight material; sp^{2} configuration of the atoms valence electrons, ensuring a flat two-dimensional structure of condensed benzenoid units; high strength of CC valence bonds responsible for exclusive mechanical strength. Chemistry that is in conflict with graphene physics expectations covers: radical character of graphene material; collective character of electronic system of graphene, preventing from localization of its response on any external impact; the molecular nature and topochemical character of graphene mechanics; the molecular nature of graphene magnetism. Each of the properties is a direct consequence of the odd electron correlation, on one hand, and ensures a high instability of graphene material, on the other. Electron correlation inhibition by deposition of graphene monolayers on substrates is seen as a promising way to solve the problem. © 2014 Wiley Periodicals, Inc.

Looking at its basic lattice chemical building block, for example, the benzenoid units, this article discusses the chemical/physical duality of graphene. The distribution of CC bond lengths correlates to the stability of the graphenic structures and can be used in fact a (quantitative) key-descriptor. It is suggested that stability in graphene on external actions can be improved by inhibiting graphene radicalization, by tuning the correlation of its odd electrons.

In this study, 12 bound complexes were selected to construct a database for testing 15 dispersion-improved exchange-correlation (XC) functionals, including hybrid generalized gradient approximation (GGA), modified using the Grimme's pairwise strategy, and double hybrid XC functionals, for specifically characterizing the CO_{2} binding by alcoholamines. Bound complexes were selected based on the characteristics of their hydrogen bonds, dispersion, and electrostatic (particularly between the positive charge of CO_{2} and the lone pair of N of alcoholamines) interactions. The extrapolated binding energy from the aug-cc-pVTZ (ATZ) to aug-cc-pVQZ (AQZ) basis set at the CCSD(T)/CBS(MP2+DZ) level was used as the reference for the XC functional comparison. M06-2X produced the optimal agreement if the optimized geometries at MP2/ATZ level were chosen for all the test bound complexes. However, M06-L, ωB97X, and ωB97, and were preferred if the corresponding density functional theory (DFT) optimized geometries were adapted for the benchmark. Simple bimolecular reaction between CO_{2} and monoethanolamine simulated using polarizable continuum solvation model confirmed that ωB97, ωB97X, and ωB97XD qualitatively reproduced the energetics of MP2 level. The inconsistent performance of the tested XC functionals, observed when using MP2 or DFT optimized geometries, raised concerns regarding using the single-point *ab initio* correction combined with DFT optimized geometry, particularly for determining the nucleophilic attack by alcoholamines to CO_{2}. © 2014 Wiley Periodicals, Inc.

Alcoholamines are part of commercially available technologies for CO_{2} capture in fossil-fuel power stations. When the accuracy of 15 dispersion-improved density functionals in describing the intermolecular interaction between CO_{2} and alcoholamines is benchmarked, the performances of the tested functionals are statistically analysed in respect to three different scenarios for the CO_{2} capturing process.

The detailed mechanisms of the Lewis acid-catalyzed transesterification of β-oxodithioesters at a solvent-free condition were studied using density functional theory. Five possible reaction pathways, including one noncatalyzed (channel 1) and four Lewis acid-catalyzed channels (SnCl_{2}-catalyzed channels 2 and 3 and SnCl_{2}·2H_{2}O-catalyzed channels 4 and 5), were investigated. Our calculated results indicate that the energy barriers of the catalyzed channels are significantly lower than that of channel 1. Channel 5, which has an energy barrier of 33.70 kcal/mol as calculated at the B3LYP/[6-31G(d, p)+LANL2DZ] level, is the most energy-favorable channel. Moreover, one water molecule of SnCl_{2}·2H_{2}O participated in the transesterification in channel 5. Thus, we report a novel function of the SnCl_{2}·2H_{2}O catalyst, which is quite different from the function of the conventional nonhydrated Lewis acid SnCl_{2}. To understand the function of these two Lewis acid catalysts better, the global reactivity indexes and natural bond orbital charge were analyzed. This work helps in understanding the function of the Lewis acid in transesterification, and it can provide valuable insight for the rational design of new Lewis acid catalysts. © 2014 Wiley Periodicals, Inc.

β-ketoesters are widely employed as starting materials in transesterification reactions. To avoid the use of harsh pH conditions, a new solvent-free transesterification process catalyzed by SnCl_{2} has been recently developed. Density functional theory calculations shine a light on the mechanism of this reaction, highlighting the effect of water in the activity of the Lewis acid catalysist SnCl_{2}.

Upon irradiation with ultraviolet wavelengths, Fe_{2}(S_{2}C_{3}H_{6})(CO)_{6}, a simple model of the [FeFe]-hydrogenase active site, undergoes CO dissociation to form the unsaturated Fe_{2}(S_{2}C_{3}H_{6})(CO)_{5} species and successively a solvent adduct at the vacant coordination site. In the present work, the CO-photolysis of Fe_{2}(S_{2}C_{3}H_{6})(CO)_{6} was investigated by density functional theory (DFT) and time-dependent DFT (TDDFT). *Trans* Fe_{2}(S_{2}C_{3}H_{6})(CO)_{5} form and the corresponding *trans* heptane or acetonitrile solvent adducts are the lowest energy ground state forms. CO dissociation barriers computed for the lowest triplet state are roughly halved with respect to those for the ground state suggesting that some low-lying excited potential energy surface (PES) could be loosely bound with respect to FeC bond cleavage. The TDDFT excited state PESs and geometry optimizations for the excited states likely involved in the CO-photolysis suggest that the FeS bond elongation and the partial isomerization toward the rotated form could take place simultaneously, favoring the *trans* CO photodissociation. © 2014 Wiley Periodicals, Inc.

Earlier studies have suggested that the irradiation of [FeFe]-hydrogenase in solution with near-UV light favors the ultrafast CO photolysis process, yielding the formation of an unsaturated species that successively binds a solvent molecule. The mechanism the photolysis process is unveiled by detailed characterization of the electronic spectrum of the system and the topology of its excited states potential energy surface, using density functional theory, and time-dependent DFT.

A chemical reaction can be understood in terms of geometrical changes of the molecular structures and reordering of the electronic densities involved in the process; therefore, identifying structural and electronic density changes taking place along the reaction coordinate renders valuable information on reaction mechanism. Understanding the atomic rearrangements that occur during chemical reactions is of great importance, and this perspective aims to highlight the major developments in quantum chemical topology analysis, based on the combination of electron localization function and catastrophe theory as useful tools in elucidating the bonding and reactivity patterns of molecules. It reveals all the expected, but still ambiguous, elements of electronic structure extensively used by chemists. The chemical bonds determine chemical reactivity, and this technique offers the possibility of their visualization, allowing chemists to understand how atoms bond, how and where bonds are broken/formed along a given reaction pathway at a most fundamental level, and so, better following and understanding the changes in the bond pattern. Their results clearly herald a new era, in which the atomic imaging of chemical bonds will constitute a new method for examining chemical structures and reaction mechanisms. The important feature of this procedure is that in practice the scope of its values is system-independent. In addition, from a practical point of view, it is cheap to calculate and implement because wave functions are the required input, which are easily available from standard calculations. To capture these results two reaction mechanisms: isomerization of C(BH)_{2} carbene and the thermal cycloheptatriene-norcaradiene isomerizations have been selected, indicating both the generality and utility of this type of analysis. © 2014 Wiley Periodicals, Inc.

Quantum chemical topology provides a set of powerful tools to visualize and evaluate the bonding and reactivity patterns of molecules. Bonding Evolution Theory describes the electronic rearrangements within chemical processes. Using the isomerization of C(BH)_{2} carbene, and thermal cycloheptatriene-norcaradiene isomerization reactions as examples, this approach is reviewed here.

The response of a molecule to static and dynamic electromagnetic fields and intramolecular perturbations is reviewed within the framework of the Rayleigh–Schrödinger perturbation theory. A semiclassical approach is adopted, using quantized form of electronic operators and the nonquantized description of the electromagnetic fields via the Maxwell equations. The Bloch multipolar gauge has been used to define operators suitable to describe the molecular interaction with nonhomogneous time-dependent perturbations. It is shown that the quantum mechanical theory of magnetic properties can profitably be proposed in terms of electronic current densities induced by an external magnetic field and permanent magnetic dipole moments at the nuclei. Theoretical relationships are reported to evaluate magnetizability, nuclear magnetic shielding, and nuclear spin-spin coupling, proving that the whole theory can be reformulated via the equations of classical electromagnetism, provided that the current density is evaluated by quantum mechanical methods. Emphasis is placed on the invariance of response properties in a translation of the coordinate system as a basic requirement for measurability. The connections among translational invariance, gauge invariance, and electron charge conservation are outlined, showing that they can be illustrated via quantum mechanical sum rules. A number of relationships describing the change of static and dynamic electromagnetic properties in a translation of the reference frame are reported. © 2014 Wiley Periodicals, Inc.

The magnetic dipole and the magnetic field induced by a circular loop of electronic current density ; below, the anapole moment , and the confined magnetic field induced by an electronic current density flowing on the surface of a geometrical torus. The magnetic dipole and the magnetic field associated with the circular loop are origin-independent. The magnetic dipole of the torus vanishes and the anapole moment is origin-independent.

The mechanism for initially divergent radical reactions reconverging to form a single product is studied using density functional theory calculations. The calculation results suggest that there are six possible pathways from reactants to products. The free energy barriers of the rate-determining steps of each pathway are almost equal. Thus, different from usual reaction, the selectivity of this reaction is determined by the relative value of free energy barriers of the two competitive reactions, that is, cyclization and bimolecular trapping, rather than that of rate-determining steps. In all reaction pathways, cyclization reaction is more competitive than bimolecular trapping reaction due to its low free energy barrier. In addition, the free energy barriers of bimolecular trapping reaction between Bu_{3}SnH and reactants are all lower than that of NCC_{6}H_{11}. However, Bu_{3}SnH is not always suitable due to its large steric repulsion. © 2014 Wiley Periodicals, Inc.

Divergent steps usually control the stereoselectivity of a reaction. Thus, if there is no selectivity in the initially divergent step, the overall reaction should always be not selective. This view is challenged in this study, where the mechanism for initially divergent radical reaction reconverging to form a single product is studied using Density Functional Theory.

The capabilities of the Crystal14 program are presented, and the improvements made with respect to the previous Crystal09 version discussed. Crystal14 is an *ab initio* code that uses a Gaussian-type basis set: both pseudopotential and all-electron strategies are permitted; the latter is not much more expensive than the former up to the first-second transition metal rows of the periodic table. A variety of density functionals is available, including as an extreme case Hartree–Fock; hybrids of various nature (global, range-separated, double) can be used. In particular, a very efficient implementation of global hybrids, such as popular B3LYP and PBE0 prescriptions, allows for such calculations to be performed at relatively low computational cost. The program can treat on the same grounds zero-dimensional (molecules), one-dimensional (polymers), two-dimensional (slabs), as well as three-dimensional (3D; crystals) systems. No spurious 3D periodicity is required for low-dimensional systems as happens when plane-waves are used as a basis set. Symmetry is fully exploited at all steps of the calculation; this permits, for example, to investigate nanotubes of increasing radius at a nearly constant cost (better than linear scaling!) or to perform self-consistent-field (SCF) calculations on fullerenes as large as (10,10), with 6000 atoms, 84,000 atomic orbitals, and 20 SCF cycles, on a single core in one day. Three versions of the code exist, serial, parallel, and massive-parallel. In the second one, the most relevant matrices are duplicated, whereas in the third one the matrices in reciprocal space are distributed for diagonalization. All the relevant vectors are now dynamically allocated and deallocated after use, making Crystal14 much more agile than the previous version, in which they were statically allocated. The program now fits more easily in low-memory machines (as many supercomputers nowadays are). Crystal14 can be used on parallel machines up to a high number of cores (benchmarks up to 10,240 cores are documented) with good scalability, the main limitation remaining the diagonalization step. Many tensorial properties can be evaluated in a fully automated way by using a single input keyword: elastic, piezoelectric, photoelastic, dielectric, as well as first and second hyperpolarizabilies, electric field gradients, Born tensors and so forth. Many tools permit a complete analysis of the vibrational properties of crystalline compounds. The infrared and Raman intensities are now computed analytically and related spectra can be generated. Isotopic shifts are easily evaluated, frequencies of only a fragment of a large system computed and nuclear contribution to the dielectric tensor determined. New algorithms have been devised for the investigation of solid solutions and disordered systems. The topological analysis of the electron charge density, according to the Quantum Theory of Atoms in Molecules, is now incorporated in the code via the integrated merge of the Topond package. Electron correlation can be evaluated at the Möller–Plesset second-order level (namely MP2) and a set of double-hybrids are presently available via the integrated merge with the Cryscor program. © 2014 Wiley Periodicals, Inc.

CRYSTAL is a general-purpose *ab initio* periodic program for the study of crystalline solids. It computes chemical and physical properties of periodic systems within Hartree–Fock, density functional or various hybrid approximations. Symmetry is fully exploited at all steps of the calculation. In this work, the last version of the code (CRYSTAL14) is presented. New capabilities and enhancements are discussed along with selected applications and performance benchmarks.

In this article, I review some of the best available quantum dynamical approaches for studying bimolecular chemical reactions. Calculating the thermal rate constant is central in theoretical chemistry and there is a focus on this. I begin by motivating the need for quantum dynamics before giving a general overview. Thereafter, I give expressions for calculating thermal rate constants. This is followed by a brief description of time-independent scattering calculations. Next comes a longer section on time-dependent approaches including the time-dependent wave packet approach, the multiconfigurational time-dependent Hartree approach and ring polymer molecular dynamics. Finally, I make some concluding remarks. © 2014 Wiley Periodicals, Inc.

The differences between reaction cross-sections calculated classically and quantum mechanically illustrate the importance of quantum dynamics in the study of bimolecular chemical reactions. Computational methods for this purpose include the traditional time-independent quantum scattering, time-dependent quantum dynamics approaches, advanced MCTDH, and path integral-based algorithms. The latter are the most accurate and computationally practical methods for investigating large quantum systems, with special focus on the calculation of thermal rate coefficients of reactions.

Magnetic exchange is an essential feature of transition-metal nanomagnets because it combines the relatively low spin-only moments of several ions into a “giant spin” ground state, which can make slow magnetic relaxation very favorable in an axially anisotropic environment. In contrast, most of the early research on lanthanide-based complexes focused on single-ion magnets, where the required large moment is generated by the unquenched orbital contribution (which is parallel to the spin in heavy rare earths). With their unfilled 5f electronic shell being on the verge between localization and itinerancy, actinides are expected to combine the best of both 3d and 4f metals in terms of exchange and anisotropy, and are therefore under consideration as potential building blocks for the next generation of single-molecule magnets. In this Perspective, a review of the recent development in this field is given, and some discrepancies between the spectroscopic and magnetic data are discussed. © 2014 European Commission. International Journal of Quantum Chemistry published by Wiley Periodicals, Inc.

Molecular complexes with slow magnetic relaxation, mainly based on 3d and 4f metals, are the subject of intensive research in such diverse fields as high-density memory recording, quantum information processes, magnetocaloric refrigeration, and spintronic applications. The use of actinide ions, whose unfilled 5f shell could carry a large ligand-field anisotropy barrier together with significant exchange interaction has been envisaged. Recent advancements in this field will be reviewed putting particular emphasis on some presently unresolved challenges.

The development of new materials with exceptional nonlinear optical properties plays a key role for present-day electronic technology. The improvement of quantum-chemical approaches for the prediction of such properties as static and dynamic first and second hyperpolarizabilities has both practical and fundamental interest. On page 689 (DOI: 10.1002/qua.24617), Vladimir Rossikhin, Eugene Voronkov, Sergiy Okovytyy, Tetiana Sergeieva, Karina Kapusta, and Jerzy Leszczynski propose an efficient procedure for the construction of physically rationalized Slater-type basis sets for calculations of dynamic hyperpolarizability. Augmentation of minimal STO-3G basis sets by first- and second-order correction functions yields cost-effective STO^{##}(II)-3G_{el} basis sets, which, at the DFT level, display better performance than well-known Gaussian-type basis sets.

The through σ-bonds spin polarization mechanism in a radical, for example, in the ethyl radical, is described by Padeleimon Karafiloglou and Katerina Kyriakidou on page 696 (DOI: 10.1002/qua.24620) as a cooperative effect of two unpaired electrons in two atomic orbitals (AOs). When the AOs belong to the same atom (i.e., to spatially orthogonal orbitals), then the probability of simultaneously finding two unpaired electrons of parallel spins is greater than for antiparallel spins, in agreement with Hund's rule. The opposite holds when the two AOs contribute to a formal chemical bond. The green and pink images on the cover represent large and small probabilities, respectively.

An efficient procedure for construction of physically rationalized Slater-type basis sets for calculations of dynamic hyperpolarizability is proposed. Their performance is evaluated for the DFT level calculations for model molecules, carried out with a series of functionals. Advantages of new basis sets over standard d-aug-cc-pVTZ and recently developed LPOL-(FL,FS) Gaussian-type basis sets are discussed. © 2014 Wiley Periodicals, Inc.

For large molecules, the cost of calculations of the dynamic hyperpolarizability plays a critical role in the selection of the most appropriate theoretical approach for the task. A novel procedure for the expansion of the Slater-type basis set for these calculations yields cost-effective physically corrected basis sets, which at the DFT level display better performance than standard d-aug-cc-pvtz and Lpol-(FL,FS) Gaussian-type basis sets.

Adopting the second-order reduced density matrix level, the conventional α- and β-spin populations in radicals are split into paired and unpaired or electropon (referring to the simultaneous occurrence of an electron and a hole of opposite spins in an orbital) populations. This analysis gives the possibility to distinguish the (un)favorable for chemical bonding electronic interactions by means of positive or negative Coulomb and/or Fermi correlations of two electropons. To overcome the conceptual difficulties originated from the subtle superposition of unpaired electrons due to spin density and those responsible for chemical bonding, we use the notion of properly unpaired electrons. The quantity describing this notion provides a global picture for the ability of electrons of a given orbital to form covalent bonds with the electrons of all remaining orbitals. More detailed information, concerning the behavior of electrons in two distinct target orbitals, is obtained by means of the two-electropon correlations. As shown, the boundary values of the used quantities are physically meaningful, and the whole theory is tested from various points of view concerning: localized and delocalized radical centers, orthogonal and nonorthogonal orbitals, uncorrelated and correlated levels, Coulomb and Fermi correlations. We also check the electropon based analysis by investigating the spin polarization effects and bond orders in radicals. The tests are achieved for well-known radicals, and to preserve the stability of the numerical results and the invariance of the obtained conceptual pictures, we used natural basis sets introduced within the natural bond orbital methodology. © 2014 Wiley Periodicals, Inc.

Second-order reduced density matrices (2-RDM) are an important tool for the study of unpaired densities. The calculation and analysis of 2-RDM in radicals show the connection of various notions such as unpaired electrons, spin polarization, and bond orders. Within the framework of 2-RDM, the conventional α- and β-spin populations of radicals are split into paired and unpaired populations.

Host–guest interactions in a new aza crown analog with alkali and alkaline earth metal ions are studied at different levels of theory. All the compounds are optimized at B3LYP/6-311+G(d) level of theory. To build the general idea about the consequence of methods of computation on the interaction energy of metal ions with the ligand, geometry optimization of some selected planar systems are carried out at the M05-2X, PBE0, wB97XD, and B3LYP-D levels. Calculated geometrical parameters, interaction energies, nucleus-independent chemical shift values, and thermodynamic properties highlight the selectivity associated with these interactions. Further insights into the nature of the bonding in these ion-macrocyclic supramolecular units are obtained through the natural bond orbital, atoms-in-molecules, bond energy decomposition, and electron localization function analyses. © 2014 Wiley Periodicals, Inc.

A new aza-crown cluster with four
ions linked together using
ions is designed and proposed for synthesis by *ab initio* calculations. The host complex, , can selectively bind metal ions. The favorable interaction energy and reaction free energy values suggest the stability of the host–guest complex. Different metal bound complexes exhibit different bonding patterns. The NTi bond exhibits a more covalent character than NLi and NMg bonds.

Möbius strip has attracted extensive interest due to its one-side structure, special physical and chemical properties. A new extended porphyrin with Möbius structure has been synthesized (Stępień et al., Angew. Chem. Int. Ed. 2007, 46, 7869). In this work, an electron is injected into Möbius to form Möbius anion. For Möbius, four methods (B3LYP, BHandHLYP, CAM-B3LYP, and LC-BLYP) obtain the similar first hyperpolarizability (*β*_{0}). However, for Möbius anion, four methods obtain very different *β*_{0} values (ranging from 9.85 × 10^{3} to 8.33 × 10^{5} au). Moreover, the *β*_{0} values of Möbius anion are larger than those of Möbius. Why? The considerable variation (ranging from 0.8162 to 1.7630) of spin contamination (*S*^{2}) of open-shell Möbius anion captures our attention. To probe the relationship between *S*^{2} and *β*_{0}, the *β*_{0} values of Möbius anion were calculated using 23 methods. Interestingly, the Hartree-Fock (HF) composition increases from 0 to 50, the *S*^{2} value ranges from 0.7522 to 1.3372, and the *β*_{0} value increases from 4.3 × 10^{3} to 7.36 × 10^{4} au. Further, methods are “dissected” to investigate the effect of HF composition on the *S*^{2}. © 2014 Wiley Periodicals, Inc.

Möbius structures exhibit a wide range of nonlinear optical properties, which make them interesting systems as potential optical switches. Several theoretical methods are compared for the study of the relationship between the spin contamination and the first hyperpolarizability of Möbius anions. The Hartree–Fock composition in various methods is found to have a large effect on the calculated value of both hyperpolarizability and spin contamination.

This work presents systematic studies of the possible classical structures of Si_{36}H_{36} and C_{36}H_{36} nanocages using density functional theory calculations. The computed structures, relative stabilities, and electronic properties of these silicon- and carbon-based hydrides are investigated and compared. The results indicate that none of the Si_{36}H_{36} or C_{36}H_{36} nanocages exhibit a perfect spherical shape. Hydrogenated nanocages with higher number of adjacent pentagons are more stable and this observation is contrary to the trend of bare fullerenes. The hydrogenated small cages are energetically more favorable than large ones according to the obtained binding energies. Moreover, the energy levels, distributions, and irreducible representations of the frontier orbital for Si_{36}H_{36} and C_{36}H_{36} nanocages are also explored. Obvious localizations within the inner space of nanocages are detected for the lowest unoccupied molecular orbital of C_{36}H_{36}. © 2014 Wiley Periodicals, Inc.

Unlike hydrogenated fullerene-[20] and [60] cages, none of Si_{36}H_{36} and C_{36}H_{36} exhibits a perfect spherical shape. The adjacent pentagons rule is invalid in the determination of the relative stability of Si_{36}H_{36} and C_{36}H_{36} nanocages. Small cages always give large energy gaps for carbon and silicon hydrides due to the quantum conferment effect. The lowest unoccupied molecular orbital of C_{36}H_{36} is mainly distributed in the inner space of the cage, indicating the possibility to host metal atoms.

A wide adiabatic study is performed for NaRb molecule, involving 15^{1}Σ^{+} electronic states including the ionic state Na^{−}Rb^{+}, as well as 14^{3}Σ^{+}, 1–9^{1,3}Π, and 1–5^{1,3}Δ states. This investigation is performed using an *ab initio* approach which involves the effective core potential, the core polarization potential with *l*-dependent cut-off functions. The NaRb system has been treated as a two-electron system and the full valence configuration interaction is easily achieved. The spectroscopic constants *R*_{e}, *D*_{e}, *T*_{e}, *ω*_{e}, *ω*_{e}*x*_{e}, *B*_{e}, and *D*_{0} for all these states are derived. We have also computed the vibrational levels as well their spacing for different values of *J*. In addition, permanent and transition dipole moments are determined and analyzed. The Dunham coefficients have been used to perform experimental spacing to compare directly with our results. The present calculations on NaRb extend previous theoretical works to numerous electronic excited states in the various symmetries. © 2014 Wiley Periodicals, Inc.

Heteronuclear alkali dimers, like NaRb, have applications in Bose–Einstein condensates, laser cooling, and photoassociative spectroscopy. Comprehensive first-principles modeling of the potential energy for all electronic states dissociating below the ionic limits of Na^{-} and Rb^{+} helps in the correct assignment of vibrational and rotational quantum numbers from experiments, and inspires new pathways in cold ions trapping research.

The time-dependent wavepacket method is used to study the reaction dynamics of S(^{3}P) + HD (*v* = 0, 1, 2) on the adiabatic 1^{3}*A*″ potential energy surface constructed by Han and coworkers [J. Chem. Phys. 2012, 136, 094308]. The reaction probabilities and integral cross sections as a function of collision energy are obtained and discussed. The results calculated by using the CC and the CS approximation have been compared, which suggests that for this direct abstraction reaction, the cheaper CS approximation calculation is valid enough in the quantum calculation. The investigation also shows that the reaction probabilities and integral cross sections tend to increase with collision energy. By analyzing the *v*-dependent behavior of the integral cross sections, the significant effect of the vibrational excitation of HD is found. Also found in the calculation is a significant resonance feature in the reaction probabilities versus collision energy. © 2014 Wiley Periodicals, Inc.

S+H_{2}/HD/D_{2} reactions are fundamental models for the study of elementary chemical reaction dynamics. The time-dependent wavepacket method is used to study reaction probabilities and integral cross sections of S(^{3}P)+HD. The investigation shows an important effect of the vibrational excitation of HD in integral cross sections and a significant resonance feature in the reaction probabilities versus collision energy.