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Kazuya Ishimura

Publications and source records attributed to Kazuya Ishimura.

3 recordsLinked to original sources
PubMed2006

A new parallel algorithm of MP2 energy calculations.

A new parallel algorithm has been developed for second-order Møller-Plesset perturbation theory (MP2) energy calculations. Its main projected applications are for large molecules, for instance, for the calculation of dispersion interaction. Tests on a moderate number of processors (2-16) show that the program has high CPU and parallel efficiency. Timings are presented for two relatively large molecules, taxol (C(47)H(51)NO(14)) and luciferin (C(11)H(8)N(2)O(3)S(2)), the former with the 6-31G* and 6-311G** basis sets (1,032 and 1,484 basis functions, 164 correlated orbitals), and the latter with the aug-cc-pVDZ and aug-cc-pVTZ basis sets (530 and 1,198 basis functions, 46 correlated orbitals). An MP2 energy calculation on C(130)H(10) (1,970 basis functions, 265 correlated orbitals) completed in less than 2 h on 128 processors.

Algorithms↗
PubMed2005

Synthesis and characterization of stable hypervalent carbon compounds (10-C-5) bearing a 2,6-bis(p-substituted phenyloxymethyl)benzene ligand.

X-ray analysis of bis(p-fluorophenyl)methyl cation bearing a 2,6-bis(p-tolyloxymethyl)benzene ligand showed a symmetrical structure (10-C-5) where the two C-O distances are identical, although the distance (2.690(4) A) is longer than those (2.43(1) and 2.45(1) A) of 1,8-dimethoxy-9-dimethoxymethylanthracene monocation, which was recently reported by us. However, X-ray analysis of the more stable aromatic xanthylium cation with the same benzene ligand showed the tetracoordinate carbon structure where only one of the two oxygen ligands is coordinated with the central carbon atom. These results clearly indicate that the carbocations (10-C-5) bearing the sterically flexible benzene ligand were quite sensitive to the electronic effect on the central carbon atom. The electron distribution analysis by accurate X-ray measurements and the density functional calculation on the initially mentioned bis(p-fluorophenyl)methyl cation clearly show that the central carbon atom and the two oxygen atoms are bonded even if the bond is weak and ionic based on the small value of the electron density (rho(r)) and the small positive Laplacian value (nabla(2)rho(r)) at the bond critical points.

Journal Article↗