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

1)对采用广义Born公式的从头算GB模型进行了修正，引入了一个空间因子，该因子考虑了分子中一个原子的溶剂层被其他原子排斥，以及(Ii)重新确定了用于计算原子半径的参数，这些参数是由Lowdin布居分析得到的原子电荷的函数。用新方法半定量计算了中性分子、阳离子和阴离子的水合能。2)用从头算GB方法成功地研究了(1)三甲基硫阳离子与氯离子的S_N反应；(2)亚乙基硫离子在硫芥酸水解反应中的结构和反应活性；(3)三卤化物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)用MC/MO杂化方法研究了二甲基一氧化氮(DMNO)超精细耦合常数在几种溶剂中的溶剂效应。在溶液的蒙特卡罗模拟中，从快照中选择了溶剂分子的构型，并对300个构型的结果进行了平均，得到了DMNO的电子结构和超精细耦合常数。认为DMNO和H_2O分子之间的电子转移是在两个方向上进行的，即N-O基团周围的DMNO到H_2O和CH_3基团附近的H_2O到DMNO。这些电子转移极化了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.