The semi-empirical MO method HAM/3 developed by Lindholm and coworkers is known to have a defect that it gives split energies for the degenerate eigenstates. We propose a group-theoretical way to remedy the defect of the HAM/3 method.
The wavefunction was obtained by the SCF calculation in which the spin-orbit coupling (SOC) interaction was included variationally. This SOC-SCF wave function was used to calculate the parity-violating energy (Epv) of the glycine zwitterion. The calculated Epv values have suggested that (1) the minimal basis sets and split-valence basis sets give qualitatively the same variation in Epv for the conformational change, (2) the magnitude of the SOC-SCF Epv is several times as large as that of the sum-over-state perturbation theory (SOS-PT) Epv and (3) the inclusion of one-center terms both of one-and two-electron spin-orbit interactions is sufficient to estimate the Epv value quantitatively.
Recently high performance rechargeable battery for movable communicator and batteries of electric automobiles is in great demand. In order to develop higher performance lithium ion rechargeable battery, it is necessary to reveal structures and mechanism of Li absorption or intercalation into carbon electrode. But it is quite difficult to experimentally reveal those structures and mechanisms, because carbon materials are amorphous clusters. We investigated structures and mechanisms of Li absorption or intercalation into carbon clusters using ab initio molecular orbital calculation, aiming at the materials design of lithium ion rechargeable battery. Using the ab initio molecular orbital calculation program Q-Chem, we examined the result of the previous carbon model using the semi-empirical molecular orbital method by Yamabe et al., and calculated electronic energy levels on our modified carbon cluster model consisting of more than 100 carbon atoms. As a result, we found an optimum structure of carbon cluster, and succeeded in the materials design of carbon electrode of lithium ion rechargeable battery.
Sulfonylallenes, R - SO2 - CHCCH2 (R= 3 - vinyl - cyclohex - 2 - en - 1 - yl (1a) and 2 - methyl - 3 - vinylcyclohex - 2 - en - 1 - yl (1b) ) undergo thermally the [4+2] Diels - Alderand [2+2] two-step intramolecular cycloadditions, the latter predominating in 1b. Thebranching between the two types of cycloadditions has been studied in terms of the transitionstates calculated semiempirically.
Conformational energy computations on homopeptides of (S)-isovaline and diethylglycine were performed using molecular mechanics on MacroModel®. Calculations of conformational search were carried out with Monte Carlo method. When AMBER* was used as force field, it was found that global minimum energy conformations were 310-helix. These results are in agreement with their reported conformational properties in the solid state, determined by X-ray crystallographic analysis. In the case of MMFF force field the global minimum of diethylglycine peptide is planar structure, which is agreement with its conformation in solution.
A molecular mechanics / molecular dynamics computational method was used to simulate methanol swelling of solvent-soluble fractions obtained from extraction of Upper Freeport bituminous coal. The pyridine-soluble (PS) and pyridine-insoluble (PI) fractions were used as coal sample. The effect of PS on methanol swelling was examined and compared with previous results for PI. As methanol molecules were added to a model compound of PS fraction under periodic boundary conditions, the potential energy of the PS-methanol system decreased and the volume of the cell increased up to the limiting number of methanol, after which the rate of increase was larger with increasing the total energy. The swelling ratio estimated from the ratio of the weight increase with the number of methanol molecules introduced was in agreement with the ratio determined experimentally from sorption data. The lighter fraction PS showed smaller changes in the total energy and a larger ratio of volume increase with introducing methanol molecule into the system.
Intramolecular Diels-Alder reactions of the title compounds have been studied semiempirically by use of the PM3 Hamiltonian. Two different types of transition states are found to be involved, and we conclude these newly found second transition states determine the substituent dependence of the reaction rates. We would like to suggest that experimental studies to search for the intermediates between the two transition states are significant.