Viliam Klimo

Spin-extended Hartree-Fock ab initio calculations for small radicals

The unrestricted Hartree-Fock method and its spin-projected and spin-extended versions are used for calculating the model correlation energy and isotropic and anisotropic hyperfine splitting constants for LiH+, BeH, BH+ and OH radicals. Results are compared with those of the method of complete configuration interaction. The gradient method of Murtagh and Sargent is employed for direct minimization of EHF electronic energy.

Quasiclassical trajectory study of H + O2 → OH + O at temperatures from 500 to 2000 K

Abstract Classical trajectory calculations for the title reaction were carried out on the new extended LEPS potential energy surface. To compare the thermalized rate constants k(T) with the results of direct experimental measurements, reaction cross sections were calculated for specific values of vibrational and rotational quantum numbers and relative translational energies. Our results predict a smaller increase of k(T) than the previous studies. The temperature dependence of dynamic characteristics for the reactive and non-reactive collisions were also examined. Finally, the influence of rotational, vibrational and translational enhancement on the characteristic features of reactive trajectories was investigated.

Study of potential curves by UHF-type methods

The characteristic features of potential energy hypersurfaces for reactions H + H2 → H2 + H, H2O → OH + H → 2H + O were studied mainly by the UMP2 method in connection with standard minimal plus bond functions basis set. The results are in good agreement with experiment and results of exact methods. The maximum error in energy differences is about 21 kJ mol-1 and in internuclear distances the maximum error covers about 0·06 a 0.

Effect of molecular mobility on the decay of free radicals in amorphous polymers: a Monte Carlo study

Abstract An algorithm has been formulated for studying the diffusion-controlled reactions in amorphous polymers. A method has been proposed based on molecular mobility and leading to migration of radical centres, their approach and decay. In a volume of dimensions 70 × 100 × 123 A , using boundary periodic conditions, an amorphous polymer system and free radicals are simulated on a diamond lattice by the Monte Carlo method. Owing to crank, kink and crankshaft motions, some of them approach one another and decay. A change in the concentration of free radicals with time and temperature has been observed by the method described.

Study of the BeH radical by UHF-type and complete configuration interaction methods

The UHF, PUHF, EHF and CCI methods have been used for calculating the isotropic and anisotropic hyperfine splitting constants and electronic energy of the BeH radical employing 6 different basis sets. In all cases, except for anisotropic h.f.s. constants for the H atom, as the quality of the basis improves (based on the energy criterion) the theoretical values approach the experimental ones.

Ab initio potential energy surface of the lowest triplet BH+2 collision complex

Abstract Important parts of the lowest triplet potential energy surface of the BH + 2 molecular system are studied at the ab initio level. Obtained topological parameters of this surface and regions of its crossing with excited surfaces are compared with results of the DIM method and with previous ab initio studies.

Spin-extended hartree—fock indo calculations

Abstract The spin-extended Hartree—Fock method in INDO approximation is presented. Mestechkins EHF equations are solved iteratively by the method of steepest descent. EHF spin and charge densities, equilibrium energies and interatomic distances for some small radicals are compared with the results of the other open-shell methods.

Spin-projected SCF INDO spin density calculations

Abstract Spin densities have been calculated by the INDO method in the parametrizations of Pople and Kaufman both without and with the projection of the UHF function. This projection impairs the results in the Pople parametrization but it improves them provided the Kaufman parametrization is used.

An effective basis set with bond functions for studying the energetics of bromine compounds

Abstract A new basis set is proposed for bromine compounds with bond functions located in the centre of the bond. The basis extends our preceding basis sets with bond functions. UMP2 calculations of enthalpies of reaction of HBr with chosen radicals using this basis set are in good agreement with experimental data.

Quasiclassical trajectory calculation of the B++H2→BH++H reaction

Abstract Quasiclassical trajectory calculations were done for the lowest triplet potential energy surface of the reaction B + +H 2 →BH + +H. The analytical form of the surface is based on ab initio points fitted by an extended LEPS function with modification for intersection of the two surfaces. The angular and translational energy distributions calculated are compared with the results of crossed molecular beam experiments. Vibrational and rotational excitation of BH + molecules, reaction cross sections, and mean lifetimes of collision complex BH 2 + are discussed as well.