Composition and experience in operation of library of molecular structures as software for large-scale calculations of infrared spectra of organic compounds

In this article we describe the composition of a library of molecular structures and evaluate its capabilities for modeling IR spectra of complicated compounds. A predictive calculation of an IR spectrum is performed for the molecule of 1-phenyl-4-(p-tolyl)-1,3-butadiene on the basis of the library of molecular structures, and the theoretical and experimental spectra of this molecule are compared.K. A. Timiryazev Agricultural Academy. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 197–201, January–February, 1993.     

“Spectroscopic” Calculations of CH Bond Dissociation Energies for Ethane, Propane, Butane, Isobutane, Pentane, Hexane, and Neopentane Using Fundamental Vibration Frequencies

The fundamental spectrum and the parameters of the potential function of a number of saturated hydrocarbon molecules are calculated in an anharmonic approximation. The calculation is performed by the variational technique using a minimal Morse-harmonic basis. The potential function is taken as the sum of the Morse function for CH bonds and the harmonic function for the skeletal and deformation vibrations. The initial approximation for the potential function is found by ab initio calculations in a 6-31G basis and refined by solving the inverse problem. The calculated CH bond dissociation energies depend significantly on the molecular structure and on the position of CH bonds in the molecule. These energies correlate well with the experimental cleavage energies of these bonds. The changes in the dipole moment of the molecule induced by vibrations were found by ab initio calculations in a 6-31G basis. The calculated IR transmission curves are in good agreement with the experimental curves.     

Calculation of the potential energy surface of a polyatomic molecule in an adiabatic approximation

V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 6, pp. 1142–1144, November–December, 1995     

“Spectroscopic” Calculation of CH and NH Bond Dissociation Energies for a Series of Primary Amines

The CH and NH bond dissociation energies were calculated by the spectroscopic method for a series of primary amines. The energies were calculated from the fundamental absorption bands in an anharmonic approximation using the Morse harmonic basis set. The results are compared with data obtained from ab initio calculations in different basis sets and experimental values. It is shown that, unlike quantum-chemical calculations, the spectroscopic method correctly reproduces the effect of the molecular structure on the CH and NH bond dissociation energies in amines.Original Russian Text Copyright © 2004 by L. A. Gribov, I. A. Novakov, A. I. Pavlyuchko, V. V. Korolkov, and B. S. Orlinson__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 999–1007, November–December, 2004.     

Method for evaluating the probability of structural isomer-isomer transformations with large numbers of quasidegenerations of the energy levels of the interactant subsystems

It is shown how the theory developed by the author and regarding the structural transformations of molecules as the result of the resonance mixing between the vibronic wave functions of the corresponding states of subsystems can be extended to the case with an arbitrary number of the resonant and quasiresonant energy levels.     

A mathematical model of photochemical transformations: Analysis of the influence of basic characteristics of the model

Basic aspects of the choice of parameters entering a system of differential equations that simulate the sequence of chemical transformations in the case of initiation of a reaction by electromagnetic pulse excitation of reactant molecules are discussed. These parameters are the probabilities of spontaneous and stimulated dipole–dipole transitions and the frequency of quantum beats that lead to the reaction. A method for an a priori estimation of optimum values of these frequencies on the basis of fundamental characteristics of intramolecular processes has been specified. It has been noted that in theoretical prediction of the course of chemical reactions, the solution of the problem in the natural coordinate system (distance between the atoms), rather than Cartesian coordinates, can be more appropriate.     

SETTING THE PROBLEM OF ORBITAL DESCRIPTION OF MOLECULAR STATES

Journal of Structural Chemistry - A method for the calculation of many-electron wave functions of atoms and molecules is reported. The method is based on the orbital representation of the wave...     

Damage and fracture: Classical continuum theories

This paper reports the research results on the continuum theory of damage which goes back to the works of Kachanov, Gurson, and Rabotnov. In these models, internal variables that generally have different mathematical structure are explicitly introduced to constitutive relations. The internal variables describe a non-oriented (using scalar damage parameters) or oriented (using different-order tensors) damage distribution in the material. Then, a fracture criterion is introduced based on mechanical or thermodynamic considerations. Models of this type are still most frequently used in the structural analysis of strength of some materials (e.g., composites). Since damage nucleation and growth are closely related to strain localization, consideration is given to formulations and methods for analyzing the stability of inelastic deformation processes. Much attention is given to the effect of the finite element mesh on simulation results, to solution algorithms for such problems, and to the possibilities of using non-local constitutive models. The studies that use gradient models are also included, because damage formation is associated with sharp spatial variations of kinematic and/or dynamic characteristics which must be described by non-classical constitutive relations (gradient, non-local, micromorphic continuum).