Electronic Structure and Molecular Chirality

基于Breit-Pauli哈密顿量和广义自旋轨道得到了自旋-轨道耦合SCF （SOC-SCF）波函数，并用于计算手性分子的宇称违反能E <pν>。SOC-SCF方法给出了l -丙氨酸两性离子（L-ALAZ）构象变化的可靠变化值E <pν>。将[5s2p/3s]基组方法应用于L-ALAZ水溶液。采用广义玻恩公式的连续统模型引入溶剂化过程，建立了两个扭转角（NH_3基为φ， CO_2基为θ）的函数图E_<pν>。在E_<pν>的（φ,θ）图中，正E_<pν>区比负E_<pν>区宽，且E_<pν>的平均值为+2.1×10^<20> hartree，说明L-ALAZ在水溶液中比D-ALAZ更不稳定，这是由于弱中性电流的违反奇偶作用。蒙特卡罗（MC）模拟和从头算自旋轨道耦合SCF （SOC-SCF）方法支持了这一结论。MC模拟L-ALAZ水溶液的每1M步提取100个溶液结构，并计算每个溶液结构中L-ALAZ-(H_2O)_n （n=1 ~ 10）簇的E_<pν>能量。计算出L-ALAZ在298K水溶液中热稳定构象的期望值E_<pν>为正。MC/MO计算也为L-ALAZ在水溶液中相对于D-ALAZ的热易接近构象的不稳定性提供了支持。

The spin-orbit-coupling SCF (SOC-SCF) wavefunction was obtained on the basis of Breit-Pauli Hamiltonian and generalized spin-orbitals and was used to calculate the parity-violating energy, E <pν> of chiral molecules. The SOC-SCF method gave a reliable variation in the E <pν> value for the conformational change of L-alanine zwitterion (L-ALAZ). The method with the [5s2p/3s] basis set was applied to L-ALAZ in aqueous solution. The solvation was introduced by the continuum model of generalized Born formula, and the E_<pν> map was created as a function of two torsion angles, φ for the NH_3 group and θ for the CO_2 group. In the (φ,θ) map of E_<pν> the positive E_<pν> area is wider than the negative one, and the averaged E_<pν> value was +2.1×10^<20> hartree, indicating that L-ALAZ is more unstable than D-ALAZ in aqueous solution due to the parity-violating weak neutral current interaction.This conclusion was supported by the Monte Carlo (MC) simulation and ab initio spin-orbit coupling SCF (SOC-SCF) method. The 100 solution structures were picked up at every 1M steps of the MC simulation of the L-ALAZ aqueous solution, and the E_<pν> energy was calculated for the L-ALAZ-(H_2O)_n (n=1-10) clusters in each solution structure. The expectation value of E_<pν> of L-ALAZ was calculated to be positive for thermally stable conformations in aqueous solution at 298K. The MC/MO calculations also provide support for the destabilization of L-ALAZ compared to D-ALAZ at thermally accessible conformations in aqueous solution.