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Abstract: The frequency and temperature dependence of dipole-quadrupole polarizability of tetrahedral P4 and adamantane molecules have been studied using first-principle all-electron density functional theory calculation. The recently developed time-dependent auxiliary density functional theory is extended for the calculation of dynamic dipole-quadrupole polarizabilities. Temperature effects are incorporated by Born–Oppenheimer molecular dynamics (BOMD) simulations recorded up to 100ps. The dynamic dipole-quadrupole polarizabilities are calculated along these trajectories. The frequency and temperature effects can be significant for the accurate calculation of dipole-quadrupole polarizability. We have also identified the main reason for the observed discrepancy between experiment and theory in the case of adamantane. [Copyright &y& Elsevier]

Abstract: Recently, two non-iterative approaches have been proposed to calculate response properties within density functional theory (DFT). These approaches are auxiliary density perturbation theory (ADPT) and the non-iterative approach to the coupled-perturbed Kohn–Sham (NIA-CPKS) method. Though both methods are non-iterative, they use different techniques to obtain the perturbed Kohn–Sham matrix. In this Letter, for the first time, both of these two independent methods have been used for the calculation of dipole–quadrupole polarizabilities. To validate these methods, three tetrahedral molecules viz., and adamantane have been used as examples. The comparison with MP2 and CCSD proves the reliability of the methodology. [Copyright &y& Elsevier]

Abstract: The effect of light metal ion decoration of the organic linker in metal-organic framework MOF-5 on its hydrogen adsorption with respect to its hydrogen binding energy (ΔB.E.) and gravimetric storage capacity is examined theoretically by employing models of the form MC6H6:nH2 where M = Li+, Na+, Be2+, Mg2+, and Al3+. A systematic investigation of the suitability of DFT functionals for studying such systems is also carried out. Our results show that the interaction energy (ΔE) of the metal ion M with the benzene ring, ΔB.E., and charge transfer (Qtrans) from the metal to benzene ring exhibit the same increasing order: Na+ < Li+ < Mg2+ < Be2+ < Al3+. Organic linker decoration with the above metal ions strengthened H2-MOF-5 interactions relative to its pure state. However, amongst these ions only Mg2+ ion resulted in ΔB.E. magnitudes that were optimal for allowing room temperature hydrogen storage applications of MOF-5. A much higher gravimetric storage capacity (6.15 wt.% H2) is also predicted for Mg2+-decorated MOF-5 as compared to both pure MOF-5 and Li+-decorated MOF-5. [ABSTRACT FROM AUTHOR]

Abstract: We present density functional theory (DFT) calculations using B3LYP/6-31++G∗∗ method to show relaxation in geometry of base pairs on cation radical formation. The changes in hydrogen bond length and angles show that in the cationic radical form the structure of the base pairs relaxes due to the distribution of charge. According to a recent study, it has been found that, upon excitation hole transfer from base to sugar occurs which results in sugar radical formation and leads to strand breakage [A. Kumar, M.D. Sevilla, J. Phys. Chem. B 110 (2006) 24181]. One hydrogen bond increases, while the other decreases in Adenine–Thymine (AT) base pair and in case of Guanine–Cytosine (GC) base pair, one bond increases and other two decrease. Same is the case with bond angles for both the base pairs. Analysis of the electron density map of Singly Occupied Molecular Orbital (SOMO) reveals that electron is transferred mainly from adenine and guanine bases in the cationic radical formation of AT and GC base pair, respectively. The reactive sites of bases have been analyzed using condensed Fukui functions in a relaxed and frozen core approximation. The effects of relaxation on the reactivity indices are also analyzed. [Copyright &y& Elsevier]

Abstract: We consider a series of dipolar organic molecules where the donor groups and the acceptor groups are separated by π-conjugation like phenyl ring or alkene chains. We have performed extensive quantum chemical calculations based on density functional theory (DFT) to calculate their linear and non-linear optical coefficients. We show that though DFT is known to overestimate the polarizabilities of quasi-linear systems, the results with proper inclusion of exchange correlation compare well with the experimental studies. On increasing the π-conjugation length, the coefficients increase non-linearly. We also vary the donor and the acceptor groups and study the role of chemical modifications on the response properties. Herein we suggest experimental methods by which the molecules may be arranged in non-centrosymmetric fashion in the bulk for device integration. [Copyright &y& Elsevier]

In this paper, we present linear and non-linear electric properties of BH, CO and H2O using a density functional response approach, which is a combination of numerical and analytical technique and is thus a simplification of fully analytic method. In the framework of an analytic response approach using Kohn–Sham (KS) density functional theory, the derivative of the KS operator with respect to external field is evaluated numerically, while the orbital derivatives and the subsequent energy derivatives are obtained fully analytically. The method is tested using three molecules BH, CO and H2O, which are marked by high degree of electron correlation and for which extensive ab initio benchmark results are available. Further, we have made a study of possible incorporation of non-dynamical electron correlation by studying BH at several inter-nuclear distances. [Copyright &y& Elsevier]

Abstract: Structural and electronic properties of Au32 cluster are analyzed using relativistic density functional theory (DFT) based methods. Further, DFT based molecular dynamical (MD) simulations are performed on Au32 golden fullerene with an aim of understanding its thermal stability at various working temperatures. Various conformations being populated at different temperatures of a cluster are analyzed. The study shows that the ground state icosahedral conformation is stable only up to 300K and structure remains in a hollow conformation only up to 400K. This clearly explains the reasons for failure by experimentalists in trapping the unique fullerene conformation in spite of the theoretical predictions of it being a very stable one. The above MD study also indicates that the bare fullerene Au32 cluster (without any stabilizing ligands) can be used for potential catalytic applications only around room temperatures. [Copyright &y& Elsevier]

Abstract: The effect of light metal (M=Li, Be, Mg, and Al) decoration on the stability of metal organic framework MOF-5 and its hydrogen adsorption is investigated by ab initio and periodic density functional theory (DFT) calculations by employing models of the form BDC:M2:nH2 and MOF-5:M2:nH2, where BDC stands for the benzenedicarboxylate organic linker and MOF-5 represents the primitive unit cell. The suitability of the periodic DFT method employing the GGA-PBE functional is tested against MP2/6-311+G* and MP2/cc-pVTZ molecular calculations. A correlation between the charge transfer and interaction energies is revealed. The metal-MOF-5 interactions are analyzed using the frontier molecular orbital approach. Difference charge density plots show that H2 molecules get polarized due to the charge generated on the metal atom adsorbed over the BDC linker, resulting in electrostatic guest-host interactions. Our solid state results show that amongst the four metal atoms, Mg and Be decoration does not stabilize the MOF-5 to any significant extent. Li and Al decoration strengthened the H2-MOF-5 interactions relative to the pure MOF-5 exhibited by the enhanced binding energies. The hydrogen binding energies for the Li- and Al-decorated MOF-5 were found to be sensible for allowing reversible hydrogen storage at ambient temperatures. A high hydrogen uptake of 4.3wt.% and 3.9wt.% is also predicted for the Li- and Al-decorated MOF-5, respectively. [Copyright &y& Elsevier]

Abstract: The Lewis acidic nature and reactivity of two industrially important catalysts, viz., Sn and Ti substituted beta zeolite (T-BEA) are analyzed using a unique combination of structural parameters, energetics and reactivity descriptors. To achieve this purpose, we adsorb the industrially important moieties (L) namely NH3, H2O, CH3OH, CH3CN on the active sites of T-BEA. The calculations were performed using a periodic density functional method where the valence electrons are described using a plane wave basis set in conjunction with pseudo-potentials for the core electrons. The analysis of the structural properties of these complexes reveals that TO4 shows typical characteristic splitting 120°/90°, close to bipyramidal geometry as compared to tetrahedral symmetry observed in the bare T-BEA. This is associated with small variations in the framework bond lengths (≥0.08Å) and a substantially large variation of bond angles (≤10°) in all the ligand-zeolite complexes. Further in both cases of Sn and Ti substituted beta zeolite, ligand interacts at optimum inter-atomic bond distance. Our interaction energies show that adsorption of all ligand moieties is stronger at Sn center than that of Ti. In general, the order of stability of the different T-BEA adducts is NH3 >H2O>CH3OH>CH3CN. The ligand interaction is associated with the corresponding bond elongation and bond reduction of the adsorbed molecules on catalyst active site, which can be taken as measure of red or blue shifted frequencies. Finally, the global descriptors of reactivity justify the fact that soft acid, Sn-BEA, interacts strongly with soft bases following the Pearson''s HSAB principle. However, hard acid, Ti-BEA interacts with soft bases to form a stable Lewis adduct. Furthermore, the HOMO–LUMO gap of all Sn-BEA–L adducts is lower than that of Ti-BEA–L adducts indicating to its higher Lewis acidic nature compared to Ti-BEA. [Copyright &y& Elsevier]

Abstract: A profile of the number of electrons with distance along the M–X bond in gas-phase diatomic molecules has been obtained from electron density plots calculated using DFT B3LYP 6-311G∗∗ method for some representative molecules. This “number profile” is compared with that expected from the partitioning of the 1D bond-distance into atom-specific transferable “hub” or core atomic sizes of the M and X atoms and another “axle” size which is associated with a pair of (bonding) electrons. The “hub” size is proportional to a core atom-specific size, rnZ c with rnZ c (M)⩾ rnZ c (X). For “single bonds”, the “hub” size for M atom is CMrnZ c (M) and for X atom is CXrnZ c (X). The “axle” size, DMX , is usually the ordinary (∼4aH /3 where aH is the Bohr radius of the hydrogen atom) or elongated (∼2aH ) bond length of the hydrogen molecule. The “hub” and “axle” sizes could be characterized “charge-transfer” (CM =π2/3 =2.144; CX =π4/3/2=2.300 and DMX = 4aH /3) or “neutral” (CM or CX =1, 2, … and DMX =2aH ). We use a new “static” or “peripatetic” classification for the core sizes which is derived from a new condition for metallization in elements based on atomic size. The charge-transfer distance, dMX ±, is usually found for “static” conditions while the “neutral” description is usually found when X=F or for “peripatetic” conditions. Such a partitioning is seen to agree with that from the plot of the total number of electrons, N el, vs r along a bond axis. The N el vs r plots from each atom are described by a simple hydrogen-atom-like function which differ away (“out”) or towards (“in”) the M–X bond. Thus N in,out(M,X)=(ZM,X ±1)exp(−r/B in,out) where the minus sign is associated with M and plus sign with X and B in,out being related inversely to the Slater orbital exponent. [Copyright &y& Elsevier]