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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Temozolomide and chloroquine are capable of forming strong H-bonds through appending groups on their aromatic systems. On page 1196 Okuma Emile Kasende, Vincent de Paul N. Nziko, and Steve Scheiner describe H-bonding and stacking interactions between the two molecules. Dispersion forces are found to be the primary factor in determining the structure of heterodimers in stacked systems. (DOI: 10.1002/qua.25152)

The interactions between temozolomide and chloroquine were examined via Dispersion-Corrected Density Functional Theory and MP2 methods. Chloroquine was considered in both its lowest energy structure and in a local minimum where its aromatic system and secondary amine group are free to interact directly with temozolomide. The accessibility of these two components to intermolecular interaction makes the lowest energy dimer of this local monomer minimum competitive in total energy with that involving chloroquine's most stable monomer geometry. In either case, the most stable heterodimer places the aromatic ring systems of the two molecules parallel and directly above one another in a stacked geometry. Most of the local minima are also characterized by a stacked geometry as well. Comparison between B3LYP and B3LYP-D binding energies confirms dispersion is a primary factor in stabilizing these structures. © 2016 Wiley Periodicals, Inc.

Temozolomide and chloroquine each contain an aromatic system conjoined with appending groups capable of forming strong H-bonds. The most important factor in the structure of heterodimers is the dispersion force between the two stacked aromatic systems. The strong intermolecular H-bonds formed by a secondary minimum of the chloroquine monomer with temozolomide can favor this heterodimer over one including the global minimum of chloroquine.

We propose a new implementation of Ehrenfest molecular dynamics based on the configuration interaction theory using configuration state functions (CSF) as basis set originally proposed by Amano and Takatsuka (J. Chem. Phys. **2005**, 122, 084113). Our development consists of two independet new features. The first one deals with the problem on how to “identify” the molecular orbitals at a simulation time step in terms of those at the previous time step. By giving an exact expression of CSF Ehrenfest method, this problem naturaly vanishes. To actually perform this method, the concept of molecular orbital connection which allows the MOs to be noncanonical is necessary. The second feature of our method is aimed to reduce the computational cost. We propose an approximaion to effectively perform the time propagation of the electron wavefunction. Due to the analogy to the locally diabatic representation method, we name our method locally quasi-diabatic representation method. In the present work, these two new features were combined and employed to perform test computations. © 2016 Wiley Periodicals, Inc.

Ehrenfest dynamics is a commonly used mixed quantum classical technique. Here, a new computational scheme for *ab initio* Ehrenfest dynamics using configuration state function as basis is proposed. One of the main features of the method is exactly connecting molecular orbitals using analytic derivative of orbital coefficients of noncanonical orbitals. In the present method, there is no switch of orbital character as in canonical orbitals.

We present accurate calculations of the non-autoionizing
and
doubly excited states of the H_{2} molecule using full configuration interaction with Hartree–Fock molecular orbitals and Heitler–London atomic orbitals. We consider the united atom configurations from He(2p2p) up to He(2p8g) and dissociation products from H_{2}(2p + 2p) up to H_{2}(2p + 6ℓ). Born–Oppenheimer calculations are carried out with extended and optimized Slater-type orbitals for a total of 40 states, 10 for each symmetry, covering the internuclear distances from the united atom to dissociation, which, for some states, is reached beyond 100 *a*_{0}. Occurrences of repulsive states cleanly interlaced between bound states with many vibrational levels are reported. Some of the potential minima are deep enough to accommodate many vibrational levels (up to 50). Noteworthy large equilibrium minima, like *R*_{eq} = 46.0 *a*_{0} in the
state dissociating as (2p + 6h) and with 18 vibrational levels. The occurrence of vertical excitations from the singly excited manifolds is analyzed. Several states present double minima generated by avoided crossings, some with a strong ionic character. © 2016 Wiley Periodicals, Inc.

Accurate computations of the potential energy curves for the H_{2} molecule are generally limited to the ground and singly excited states, because of computational challenges in computing potential energy curves for multiple-excited states. Accurate Full CI calculations, from the united atom to dissociation, for doubly excited states of the ^{1,3}
and ^{1,3}
manifolds are performed in this work, notably using Slater Type Orbitals.

The behavior of a driven symmetric triple well potential has been studied by developing an algorithm where the well-established Bohmian mechanics and time-dependent Fourier Grid Hamiltonian method are incorporated and the quantum theory of motion (QTM) phase space structures of the particle are constructed, both in “nonclassical” and “classical” limits. Comparison of QTM phase space structures with their classical analogues shows both similarity as well as dissimilarities. The temporal nature and the spatial symmetry of applied perturbation play crucial roles in having similar phase space structures. © 2016 Wiley Periodicals, Inc.

Triple well potential is a very good model for the study of the reaction dynamics of isomerization process among three species, as the three wells can represent the three species. Here, an algorithm for solving the “classical” Schrödinger equation using Bohmian mechanics and time-dependent Fourier Grid Hamiltonian method has been developed and applied to a driven symmetric triple well system.

The possible noncovalent lone pair-π/halogen bond (lp···π/HaB) complexes of perhalogenated unsaturated C_{2}Cl_{n}F_{4−n} (*n* = 0–4) molecules with four simple molecules containing oxygen or nitrogen as electron donor, formaldehyde (H_{2}CO), dimethyl ether (DME), NH_{3}, and trimethylamine (TMA), have been systematically examined at the M062X/aug-cc-pVTZ level. Natural bond orbital (NBO) analysis at the same level is used for understanding the electron density distributions of these complexes. The progressive introduction of Cl atom on C_{2}Cl_{n}F_{4−n} influences more on the lp···π complexes over the corresponding HaB ones. Within the scope of this study, gem-C_{2}Cl_{2}F_{2} is the best partner molecule for lp···π interaction with the simple molecules, coupled with the greatest interaction energy (IE) and second-order orbital interaction [*E*(2) value], whereas C_{2}F_{4} is the poorest one. The C_{2}Cl_{3}F·H_{2}CO and C_{2}Cl_{4}·H_{2}CO complexes exhibit reverse lp···π bonding, while the Z/E-C_{2}Cl_{2}F_{2}·NH_{3}, C_{2}Cl_{3}F·NH_{3} and C_{2}Cl_{4}·NH_{3} complexes perform half-lp···π bonding according to the NBO analysis. The lp···π interaction involving the oxygen/nitrogen and the π-hole of C_{2}Cl_{n}F_{4−n} overwhelms the HaB involving the oxygen/nitrogen and the σ-hole of the Cl atom. The electron-donating methyl groups contribute significantly to the two competitive interactions, therefore, DME and TMA engage stronger in the partner molecules than H_{2}CO and NH_{3}. Our theoretical study would be useful for future experimental investigation on noncovalent complexes. © 2016 Wiley Periodicals, Inc.

Complexes of chlorofluorocarbons (freons) with oxygen/nitrogen containing simple molecules are studied as models of noncovalent interaction. The possible noncovalent lone pair-π/halogen bond (lp···π/HaB) complexes of formaldehyde, dimethyl ether, ammonia and trimethylamine with perhalogenated unsaturated C_{2}Cl_{n}F_{4−}_{n} (*n* = 0–4) molecules have been systematically examined at the M062X/aug-cc-pVTZ level. For these model systems, the lp···π interaction overwhelms the halogen bond, and gem-C_{2}Cl_{2}F_{2} is the best partner molecule for lp···π interaction with the simple molecules.

The substituent effects in aerogen bond interactions between ZO_{3} (Z = Kr, Xe) and different nitrogen bases are studied at the MP2/aug-cc-pVTZ level of theory. The nitrogen bases include the sp bases NCH, NCF, NCCl, NCBr, NCCN, NCOH, NCCH_{3} and the sp^{3} bases NH_{3}, NH_{2}F, NH_{2}Cl, NH_{2}Br, NH_{2}CN, NH_{2}OH, and NH_{2}CH_{3}. The nature of aerogen bonds in these complexes is analyzed by means of molecular electrostatic potential, electron localization function, quantum theory atoms in molecules, noncovalent interaction index, and natural bond orbital analyses. The interaction energy (*E*_{int}) ranges from −4.59 to −9.65 kcal/mol in the O_{3}Z···NCX complexes and from −5.30 to −13.57 kcal/mol in the O_{3}Z···NH_{2}X ones. The dominant charge-transfer interaction in these complexes occurs across the aerogen bond from the nitrogen lone-pair (n_{N}) of the Lewis base to the *σ**_{Z-O} antibonding orbital of the ZO_{3}. Besides, the formation of aerogen bond tends to decrease the ^{83}Kr or ^{131}Xe chemical shielding values in these complexes. © 2016 Wiley Periodicals, Inc.

A new sort of σ-hole interaction between covalently bonded group 18 atoms (known as rare gases or aerogens) was recently identified and named “aerogen bonding.” Aerogen bonds are comparable in strength to hydrogen bonds and other σ-hole-based interactions. First-principle modeling can provide an insight into the substituent effects in aerogen-bonded complexes. The formation of aerogen bond tends to decrease the ^{83}Kr or ^{131}Xe chemical shielding values in these complexes.

It is shown that the Pauli potential in bound Coulomb systems can in good approximation be composed from the corresponding atomic fragments. This provides a simple and fast procedure how to generate the Pauli potential in bound systems, which is needed to perform an orbital-free density functional calculation. The method is applicable to molecules and solids. © 2016 Wiley Periodicals, Inc.

The Pauli potential fulfills to a large extend the criteria of transferability and as such can be composed from its atomic fragments. This model provides a simple and fast procedure how to generate the Pauli potential of bound systems applicable in orbital-free density functional calculations of molecules and solids.