Development of ab initio method including solvent effects and applications to chemical reactions in solution

1)通过（i）引入一个位阻因子，该位阻因子解释了分子中一个原子的溶剂壳层被其它原子排斥，及（ii）重新─确定用于评估原子半径的参数，所述原子半径表示为通过Lowdin布居分析获得的原子电荷的函数。2）将从头算GB方法成功地应用于（1）三甲基锍阳离子与氯离子的S_N反应，（2）亚乙基锍离子在芥子气水解中的结构和反应活性，（3）三卤阴离子在溶液中的结构和反应活性，（4）氨基酸两性离子在水溶液中的构象分析;（3）应用MC/MO杂化方法研究了二甲基一氧化氮自由基（DMNO）在几种溶剂中的超精细偶合常数的溶剂效应。从溶液的Monte Carlo模拟中的快照中选择溶剂分子的构型，通过平均300个构型的结果得到DMNO的电子结构和超精细耦合常数。DMNO和H_2O分子之间的电子转移是两个方向的，即在N-O基团附近从DMNO到H_2O的电子转移和在CH_3基团附近从H_2O到DMNO的电子转移。这些电子转移破坏了N-O键，增加了N原子的hfcc。

1) ab initio GB model in which solvent effect is incorporated into ab initio SCF calculations using generalized Born formula was modified was modified by (i) introducing a steric factor which accounts for the exclusion of the solvent shell of an atom in a molecule by the other atoms, and (ii) re-determination of the parameters used to evaluate the atomic radii which are expressed as a function of the atomic charge obtained by Lowdin population analysis. The hydration energies of neutral molecules, cations and anions are calculated semi-quantitatively by new version of the method.2) The ab initio GB method has been applied successfully to (1) the S_N reaction of the trimethylsulfonium cation with chloride anion, (2) structure and reactivity of ethylenesulfonium ion in hydrolysis of sulfur mustard, (3) structure and reactivity of trihalide anions in solution, and (4) conformational analysis of amino acid zwitterions in aqueous solution.3) MC/MO hybrid method was applied to elucidate the solvent effect of hyperfine coupling constants of dimethyl nitric oxide radical (DMNO) in several solvents. The configurations of the solvent molecules were selected from the snapshots in the Monte Carlo simulation for the solution and the electronic structure and the hyperfine coupling constat of DMNO were obtained by averaging the results of 300 configurations. It was recognized that the electron transfer occurs between DMNO and H_2O molecules in two directions, form DMNO to H_2O around the N-O group and from H_2O to DMNO around the CH_3 groups. These electron transfers polarize the N-O bond and increase hfcc of the N atom.