We developed a full variational molecular orbital method by which centers and exponents in a Gaussian-type function basis set are optimized automatically, as well as the molecular orbital coefficients. In the present study, we observed the behavior of wave functions with flexible basis functions for fictitiously changing the electron mass to examine the flexibility of the method. We performed two types of computational scientific simulations by decreasing and increasing the electron mass. First, we demonstrated electron transfer together with the basis function on a computer. Second, we studied the change of the wave function of the electron from delocalized to localized by increasing its mass. As test models, we used a Li^-...H⁺ system for the first simulation, and an H₂⁺ ion having a symmetrical potential for the second simulation.

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In ab initio molecular orbital calculations, two-electron integral computing timesaccount for more than 99 % of the total computing times. We are now developing a special-purpose machine MOEngine, which accelerates the calculations of two-electron integrals with high-performance and cost-effectiveness. Methods for two-electron integral calculations consist of mainly two steps, 1) computing auxiliary s-type integrals [0]^(m), 2) computing two-electron integrals by using [O] ^(m). MOEngine accelerates the step 2) by the Obara's recurrence formula. This is very effective when we compute the integrals in which each orbital has high total angular momentum, like [dd|dd]. However, these recurrence calculation steps 2) is quite less when we compute the integrals in which each orbital has low total angular momentum, like [ss|ss] and [ps|ss]. Here we discuss the efficient and high-performance computing methods for the auxiliary s-type integrals [O]^(m) by MOEngine.

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HF/6-311G^** and B3LYP/6-311G^** calculations of tetrachlorodibenzo-p-dioxins (TCDDs) predicted that the lowest-energy isomer is not the most toxic 2, 3, 7, 8-TCDD isomer but l, 3, 6, 8-TCDD. This is contrary to the AM1 and PM3 predictions which are used for the elucidation of the isomer distribution of the TCDD homologue in combustion-derived samples.

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Catechins are a group of polyphenolic compounds abundantly contained in green tea. It is well known that catechins have multiple biological activities including anticarcinogenic and antiinflammatory effects. These protective effects are due to their antioxidative activities by scavenging free radicals. All C-H and O-H bond dissociation enthalpies (BDE's) in catechins ((-) -epicatechin, (-) -epigallocatechin, (-) -epicatechin gallate, (-) -epigallocatechin gallate) were calculated by semiempirical molecular orbital method using SPARTAN program. The BDE's of benzyl hydrogens (C-2 position in catechins) are found to be quite low. This result suggests that abstraction of benzyl hydrogen is a crucial step for antioxidant activity. This is also supported by the reported results of LC/MS/MS and spectrophotometric analysis of reaction intermediate from catechins treated with AAPH.

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The catalytic behavior of inorganic acid, H₂SO₄, in Beckmann rearrangement of cyclohexanone oxime toε-caprolactam was studied by means of density functional theory calculation. It was suggested that the superiority of H₂SO₄ as acid catalyst is due to its both donor and acceptor ability of proton. By this function of H₂SO₄ the Beckmann rearrangement catalyzed by H₂SO₄ completed through simple reaction coordinate.

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