No abstract

Main characteristics are described of the PRIRODA quantum chemical program suite designed for the study of complex molecular systems by the density functional theory, at the MP2, MP3, and MP4 levels of multiparticle perturbation theory, and by the coupled cluster single and double excitations method (CCSD) with the application of parallel computing. A number of examples of calculations are presented.The year 1998 was marked by the award of the 1998 Nobel prize in chemistry to Walter Kohn "for his develop ment of the density functional theory" and John Pople "for his development of computational methods in quan tum chemistry". Outstanding advances in quantum chem istry made in the last two decades, combined with rapid progress of hardware, have made quantum chemical cal culations an integral part of applied and basic research in chemistry and related fields. Most theoretical studies of the structure and properties of molecular systems involve investigations of the adiabatic potential energy surfaces of the ground and, more rarely, excited electronic states. Often, such investigations are restricted to (i) location of the energy minima corresponding to the equilibrium ge ometries of stable states and saddle points (transition state geometries), and (ii) quadratic approximation of the potential energy surface based on the results of calcula tions of the second derivatives of energy with respect to nuclear coordinates. Besides, some applications require calculations of energy derivatives with respect to the strength of disturbing external uniform electric or mag netic field (polarizability, magnetic susceptibility, NMR shielding tensor, and Raman intensity and polarization calculations). Here, the main difficulty is solving the many electron problem, which can only be done using simplified approaches that can be divided into three types, namely, the wave function methods, density functional methods, and semiempirical methods.Ab initio methods, especially coupled cluster methods, allow, at least in principle, the nonrelativistic many elec tron problem to be solved with prescribed accuracy using converging sequences of one electron basis sets and tak

No abstract

The effect of counterion on the kinetics and mechanism of ethylene polymerization by the zirconocene−boron catalytic system was examined using the density functional theory approach. A comparative study of three model catalytic species, namely, ethylzirconocene cation, Cp2ZrEt+, and two ion pairs of composition Cp2ZrEt+A- (A- = CH3B(C6F5)3 -, B(C6F5) 4 -) was carried out. It was shown that the nature of counterion affects mainly the ratio between the most stable β-agostic and nonagostic Cp2ZrEt+A- isomers, the thermodynamic and kinetic characteristics of ethylene addition to the Cp2ZrEt+A- ion pairs, and the chain propagation kinetics. The weaker the nucleophilicity of the counterion, the higher the fraction of the β-agostic isomer, the higher the exotermicity, and the lower the activation barrier to ethylene addition to Cp2ZrEt+A-, and the lower the activation energy of chain propagation. All possible pathways of the interaction between Cp2ZrEt+CH3B(C6F5)3 - and ethylene molecule were examined and compared. Among all species of composition Cp2ZrEt+CH3B(C6F5)3 -, the nonagostic isomer was found to be the most reactive toward ethylene.