Department of Chemistry , University of Illinois , Urbana , Illinois 61801 , United States.
Department of Physics , University of Illinois , Urbana , Illinois 61801 , United States.
J Chem Theory Comput. 2018 Nov 13;14(11):5446-5458. doi: 10.1021/acs.jctc.8b00179. Epub 2018 Oct 22.
We recently presented a simple, classical trajectory-based method for generating the Wigner phase space density using classical trajectories evolving under an adiabatically switched potential. The adiabatically switched Wigner (ASW) distribution is an approximation to the exact Wigner function, which was found to be highly accurate on model systems. In this paper we discuss the implementation of the ASW procedure to polyatomic molecules both in normal mode coordinates and in Cartesian coordinates. We present its application to a six-degree-of-freedom model based on an ab initio quartic potential energy surface developed for formaldehyde in the normal mode representation and for butyne in Cartesian coordinates using the CHARMM force field. Comparisons of equilibrium properties against accurate quantum mechanical results indicate that the ASW is reliable and highly accurate over a wide temperature range in both the coordinate systems. Further, the ASW density is invariant under classical evolution, thus it is ideally suited to quasiclassical trajectory simulations. We also describe a very simple ASW-based procedure for obtaining complex-valued quasiclassical time correlation functions and vibrational spectra.
我们最近提出了一种简单的、基于经典轨道的方法，用于使用在绝热切换势下演化的经典轨道生成维格纳相空间密度。绝热切换维格纳（ASW）分布是对精确维格纳函数的一种近似，在模型系统中发现它具有很高的准确性。在本文中，我们讨论了在正常模式坐标和笛卡尔坐标中对多原子分子实施 ASW 程序的方法。我们将其应用于一个六自由度模型，该模型基于为甲醛在正常模式表示和丁炔在笛卡尔坐标中使用 CHARMM 力场开发的从头算四次势能表面。与精确量子力学结果的平衡性质比较表明，在两种坐标系中，ASW 在很宽的温度范围内都是可靠且高度准确的。此外，ASW 密度在经典演化下是不变的，因此非常适合准经典轨迹模拟。我们还描述了一种非常简单的基于 ASW 的方法，用于获得复值准经典时间相关函数和振动光谱。
