改进的凝聚相准质心分子动力学力矩估计器
Improved torque estimator for condensed-phase quasicentroid molecular dynamics
摘要：
我们描述了改进的准质心分子动力学（QCMD）的路径积分方法，这是最近开发的计算凝聚相系统的红外光谱。主要的发展是一个改进的估计分子间扭矩的准质心。当应用到qTIP 4P/F液态水和冰，新的估计被发现，以消除人为的25厘米$^{-1}$红移从天平动带，稍微增加的OH拉伸带的强度在液体中，并减少小的误差之前指出的QCMD径向分布函数。我们还修改了绝热QCMD算法中使用的质量标度，这使得分子动力学时间步长增加了四倍，从而将QCMD计算的费用降低到300 K时qTIP 4P/F液态水的笛卡尔质心分子动力学的两倍，以及150 K时冰的八倍。
英文摘要：
We describe improvements to the quasicentroid molecular dynamics (QCMD) path-integral method, which was developed recently for computing the infrared spectra of condensed-phase systems. The main development is an improved estimator for the intermolecular torque on the quasicentroid. When applied to qTIP4P/F liquid water and ice, the new estimator is found to remove an artificial 25 cm$^{-1}$ red shift from the libration bands, to increase slightly the intensity of the OH stretch band in the liquid, and to reduce small errors noted previously in the QCMD radial distribution functions. We also modify the mass-scaling used in the adiabatic QCMD algorithm, which allows the molecular dynamics timestep to be quadrupled, thus reducing the expense of a QCMD calculation to twice that of Cartesian centroid molecular dynamics for qTIP4P/F liquid water at 300 K, and eight times for ice at 150 K.
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