Schwartz Craig P, Uejio Janel S, Saykally Richard J, Prendergast David
Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Chem Phys. 2009 May 14;130(18):184109. doi: 10.1063/1.3125509.
We report the effects of sampling nuclear quantum motion with path integral molecular dynamics (PIMD) on calculations of the nitrogen K-edge spectra of two isolated organic molecules. s-triazine, a prototypical aromatic molecule occupying primarily its vibrational ground state at room temperature, exhibits substantially improved spectral agreement when nuclear quantum effects are included via PIMD, as compared to the spectra obtained from either a single fixed-nuclei based calculation or from a series of configurations extracted from a classical molecular dynamics trajectory. Nuclear quantum dynamics can accurately explain the intrinsic broadening of certain features. Glycine, the simplest amino acid, is problematic due to large spectral variations associated with multiple energetically accessible conformations at the experimental temperature. This work highlights the sensitivity of near edge x-ray absorption fine structure (NEXAFS) to quantum nuclear motions in molecules, and the necessity of accurately sampling such quantum motion when simulating their NEXAFS spectra.
我们报告了利用路径积分分子动力学(PIMD)对核量子运动进行采样,对两个孤立有机分子氮K边光谱计算的影响。三聚氰胺是一种典型的芳香族分子,在室温下主要处于其振动基态,与通过基于单个固定原子核的计算或从经典分子动力学轨迹提取的一系列构型所获得的光谱相比,当通过PIMD纳入核量子效应时,其光谱一致性有显著改善。核量子动力学可以准确解释某些特征的固有展宽。甘氨酸是最简单的氨基酸,由于在实验温度下与多个能量上可及的构象相关的大光谱变化而存在问题。这项工作突出了近边X射线吸收精细结构(NEXAFS)对分子中量子核运动的敏感性,以及在模拟其NEXAFS光谱时准确采样这种量子运动的必要性。