Showing papers by "Seiji Tsuzuki published in 1994"

Basis set effects on the intermolecular interaction of hydrocarbon molecules obtained by an ab initio molecular orbital method : evaluation of dispersion energy

Abstract: The intermolecular interaction potentials of methane, ethane, ethylene and benzene dimers were calculated using several basis sets [up to 6–311G(3d,4p)] with electron correlation correction by the Moller-Plesset perturbation method and basis set superposition error (BSSE) correction. The calculated interaction energies considerably depend on the basis set used. Whereas the interaction energies of the repulsive and Coulombic energy components calculated at the HF level are not affected by the change of the basis set, the dispersion energy component, calculated as the electron correlation energy, greatly depends on the basis set used. A basis set with multiple polarized functions is necessary to calculate the dispersion energy correctly. The use of small basis sets greatly underestimates the dispersion energy.

Refinement of Nonbonding Interaction Potential Parameters for Methane on the Basis of the Pair Potential Obtained by MP3/6-311G(3d,3p)-Level ab Initio Molecular Orbital Calculations: The Anisotropy of H/H Interaction

Abstract: The intermolecular interaction energies of 132 geometrical configurations of methane dimers were calculated by an MP3/6-311G(3d,3p)-level ab initio method. Nonbonding interaction parameters were fitted using three models (isotropic hydrogen, anisotropic hydrogen, and anisotropic hydrogen with electrostatic interaction) to reproduce the ab initio results. The incorporation of the anisotropy of the nonbonding interaction of hydrogen decreased the RMS error drastically. On the other hand, the incorporation of the electrostatic interaction improved the fitting little. The density, heat of evaporation, and self-diffusion coefficient of liquid methane were calculated by molecular dynamics simulations with the second- and the third-model parameters

Reconsideration of the stereoelectronic effect in oxyphosphorane species

Abstract: Properties of various oxyphosphoranes such as neutral pentahydroxyphosphorane (doubly protonated 3b) and dianionic trihydroxyphosphorane (3b) and trimethoxyphosphorane (3a) were examined by ab initio molecular orbital calculations. The energies of the stationary points were evaluated at the MP2 level of theory with the 6-31+G * basis. The analysis of the oxyphosphorane species indicates that the orientation of the equatorial methoxyl group determines the mode of formation/cleavage of the axial P-O 2 /P-O 5 bond. This dependence of the reactivity on the conformation of the equatorial P-O 3 bond is in accord with the prediction that is based on the stereoelectronic effect

13C NMR and ESR Studies on a Polydiacetylene Having Acetylenic Carbons in the Side Chains

Abstract: The 13C NMR spin-lattice relaxation times and ESR spectra were measured for a polydiacetylene obtained by the solid-state polymerization of a tetrayne with n-C14H29 alkyl substituents (14-4A-14). Poly(14-4A-14) has two different side chains. One side chain contains two conjugated acetylenic bonds directly bound to the main backbone conjugated system; the other is an alkyl chain. Although the unpaired electron density of poly(14-4A-14) measured by ESR is less than that in trans-polyacetylene, paramagnetic effects may contribute to the long 13C relaxation times of unsaturated carbons, which provides insight concerning the π-electron structure on the conjugated system.