Journal of Theoretical and Computational Chemistry

The geometry structure, vibrational frequency, and the isomerization of neutral and cation copper cyanide systems (CuCN and CuCN⁺) were investigated by employing three DFT methods (B3LYP, B3P86 and B3PW91) and MP2 functional with 6-311+G* basis set. The cyanides CuCN(¹Σ⁺) is the most stable one among the isomers of CuCN, and CuNC⁺(²Σ⁺) isocyanides is the global minimum on its potential energy surface (PES). The vibrational modes of these isomers were assigned. Two dissociation mechanisms were designed for each species. The complex (CuCN and CuCN⁺) tends to dissociate through neutral mechanism into CN cluster. The useful information is brought forward about the synthesis of material and biological macromolecule. The state–state isomerization pathways were established using the intrinsic reaction coordinate (IRC).

Long-wavelength electronic absorption spectra of 4-hydroxy-1-naphthaldehyde, its dimer complexes, and 4-hydroxy-3-(piperidine-1-ylmethyl)-1-naphthaldehyde are investigated using time-dependent density functional theory with the TPSSh functional within a continuum solvation model. The results are correlated to recent experimental findings on solvent-, pH- and concentration-dependent absorption. It is confirmed that with decreasing wavelength the spectrum is dominated by the deprotonated (360 nm–400 nm), the dimer (340 nm–370 nm) and the monomer (< 280 nm) species. The potential use of hydroxynaphthaldehydes for the design of tautomeric switches is discussed.

The adsorption of a series of alkyl halides, RX (X=Cl, Br, I) over acidic zeolite has been investigated by the ONIOM2 method. A 56T model cluster constructed from 55 Si atoms and one tetrahedral Al atom with one Brönsted acid site, has been used to represent the zeolite catalyst. Density functional theory (DFT) and specifically, the two layered schemes B3LYP/6-31+G(d,p)genECP:UFF and M06-2X/6-31+G(d,p)genECP:UFF have been employed, augmented with the addition of extra polarization functions for the proper treatment of the halogen atoms. Examination of selective structural changes and the computed adsorption enthalpies, ΔH_ad, of the van der Waals 1:1 adsorption complexes assumingly formed, shows a strong dependence both on the theoretical method and the alkyl radical structure. A modest influence of the halogen atom involved is also observed. The comparison of the performance of the two functionals underlines the higher capacity of the M06-2X functional to provide a more satisfactory description of the adsorption process and the contribution of the van der Waals dispersion forces.

Ketenes are excellent precursors for catalytic asymmetric reactions, creating chiral centers mainly through addition across their C=C bonds. Density functional theory (DFT) calculations at the MO6/LACVP* and B3LYP/LACVP* levels of theory were employed in a systematic investigation of the peri-, chemo- and regio-selectivity of the addition of transition metal oxo complexes of the type ReO₃L(L=Cl^-, O^-, OCH₃, CH₃) to substituted ketenes O=C=C(CH₃)(X) [X=CH₃, H, CN, Ph] with the aim of elucidating the effects of substituents on the mechanism of the reactions. The [2 + 2] addition pathway across the C=C or C=O (depending on the ligand) is the most preferred in the reactions of dimethyl ketene with all the metal complexes studied. The [2 + 2] pathway is also the most preferred in the reactions of ReO₃Cl with all the substituted ketenes studied except when X=Cl. Thus of all the reactions studied, it is only the reaction of ReO₃Cl with O=C=C(CH₃)(Cl) that prefers the [3 + 2] addition pathway. Reactions of dimethyl ketene with ReO₃L favors addition across C=O bonds of the ketene when L=O^- and CH₃ but favors addition across C=C bonds when L=OCH₃ and Cl. In the reactions of ReO₃Cl with substituted ketenes, addition across C=O bonds is favored only when X=H while addition across C=C bonds is favored when X=CH₃, Cl, Ph, CN. The reactions of dimethyl ketene with ReO₃L will most likely lead to the formation of an ester precursor in each case. A zwitterionic intermediate is formed in the reactions except in the reactions of . The order in the activation energies of the reactions of dimethyl ketenes with the metal complexes ReO₃L with respect to changing ligand L is O^- < CH₃O^- < Cl^- < CH₃ while the order in reaction energies is CH₃ < CH₃O^- < O^- < Cl^-. For the reactions of substituted ketenes with ReO₃Cl, the order in activation barriers is CH₃ < Ph < CN < Cl < H while the reaction energies follow the order Cl < CH₃ < H < Ph < CN. In the reactions of dimethyl ketenes with ReO₃L, the trend in the selectivity of the reactions with respect to ligand L is Cl^- < CH₃O^- < CH₃ < O^- while the trend in selectivity is CH₃ < CN < Cl < Ph in the reactions of ReO₃Cl with substituted ketenes. It is seen that reactions involving a change in oxidation state of metal from the reactant to product have high activation barriers while reactions that do not involve a change in oxidation state have low activation barriers. For both [3 + 2] and [2 + 2] additions, low activation barriers are obtained when the substituent on the ketene is electron-donating while high activation barriers are obtained when the substituent is electron-withdrawing.

Recently, the information theory of quantum-mechanical systems has aroused the interest of many theoretical physicists. This is due to the fact that it provides a deeper insight into the internal structure of the system. Also, it is the strongest support of the modern quantum computation and information, which is a basic theory for numerous technological developments. This study reports the solution of Schrödinger equation with the ring-shaped Mie-type potential. The rotational-vibrational spectroscopic study of some few selected diatomic molecules are given. The probability distribution density of the system which gives the probability density for observing the electron in the state characterized by the quantum numbers (n, l, m) in the ring-shaped Mie-type potential is obtained. Finally, the analysis for this distribution via a complementary information measures of a probability distribution known as the Fisher's information have been presented.

The nonadditivity of stacking interactions in stacked structures of adenine–thymine and guanine–cytosine base pairs is investigated by MP2 and SCS-MP2 calculations with 6-311++G** and aug-cc-pvdz basis sets. The calculation results indicate that the intermolecular distances in the multi-stacked structures do not become shorter obviously as the stacked structure added. The middle stacking interaction energies in the multi-stacked structures also become weaker than that of dimer structures. It is found that the total stacking interaction energies of the trimer and tetramer stacked structures do not increase proportionally. Based on the results, we suggest that there is negative cooperativity of the stacking interactions in the adenine–thymine and guanine–cytosine stacked structures.

The electron density and conductivity studies of 2,5-diphenyl-1,3,4-oxadizole organic light emitting diode (OLED) based molecule have been calculated from the quantum chemical calculations and combined with the Bader's AIM theory. Density functional theory calculations with B3LYP/aug-cc-PVDZ basis sets was used to determine ground state gas space molecular geometries (bond lengths and bond angles), electron density and bonding features of this molecule. The electron densities at the bond critical point (BCP) of aromatic Car–Car bonds are much stronger than the other bonds in the molecule. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The HOMO–LUMO gap calculated from quantum chemical calculations has been compared with the value calculated from the density of states. The negative electrostatic potential (ESP) is concentrated solely around the N atoms, whereas in the rest of the region a positive ESP to dominate.

A major portion (∼98%) of the quantum-classical molecular dynamics approach, namely, Time-Dependent Discrete Variable Representation (TDDVR) method, is recently parallelized using shared-memory parallelization scheme with the aim of performing dynamics on relatively large molecular systems. Therefore, we have chosen the furan as a model system for dynamical simulation. Four lowest singlet excited electronic states ¹A₂(3s), ¹B₂(V), ¹A₁(V*), and ¹B₁(3p) of furan are vibronically coupled through several conical intersections in the vicinity of Frank-Condon region. The major focus of the present paper is to explore the efficiency of our newly implemented parallelized TDDVR algorithm to perform dynamics on large dimensional quantum systems in vibronically coupled electronic manifold. The present version of parallelized TDDVR algorithm show closely linear speed up with increasing number of computing processors. As a significant speed up is achieved by cycling in the correct way over arrays, all dynamical simulations are performed within a reasonable wall clock time. The photoelectron spectra calculated by the TDDVR method show peak by peak correspondence with the experimental spectra. The TDDVR calculated quantum-classical dynamical outcomes, viz., population and photoelectron spectra, etc. show good agreement with the findings of the well-established quantum dynamical method, i.e. Multi Configuration Time-Dependent Hartree (MCTDH) approach.