There are a variety of methods for including nuclear quantum effects in dynamics simulations by combining quantum Boltzmann statistics with classical dynamics. Among them are thermostatted ring-polymer molecular dynamics (TRPMD), centroid molecular dynamics (CMD), quasi-centroid molecular dynamics (QCMD), and the linearised semi-classical initial value representation (LSC-IVR). Here we make a systematic comparison of these methods by calculating the infrared spectrum of water in the gas phase, and in the liquid and ice phases (using the q-TIP4P/F model potential). Some of these results are taken from previous work, and some of them are new (including the LSC-IVR calculations for ice, and extensions of all the spectra into the near-infrared region dominated by overtone and combination bands). Our results suggest that QCMD is the best method for reproducing fundamental transitions in the spectrum, and that LSC-IVR gives the best overall description of the spectrum (albeit with large errors in the bend fundamental band caused by zero-point-energy leakage). The TRPMD method gives damped spectra that line up with the QCMD spectra, and is by far the cheapest method.

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哪种量子统计-经典动力学方法最适合水？

通过将量子玻尔兹曼统计量与经典动力学相结合，可以采用多种方法将核量子效应包括在动力学模拟中。其中包括恒温环聚合物分子动力学（TRPMD），质心分子动力学（CMD），准质心分子动力学（QCMD）和线性化的半经典初始值表示（LSC-IVR）。在这里，我们通过计算气相，液相和冰相中水的红外光谱（使用q-TIP4P / F模型电势）来对这些方法进行系统的比较。这些结果中的一些取自先前的工作，而另一些则是新的（包括LSC-IVR的冰计算，以及将所有光谱扩展到以泛音和组合谱带为主的近红外区域）。我们的结果表明，QCMD是再现频谱中基本跃迁的最佳方法，而LSC-IVR提供了频谱的最佳整体描述（尽管由于零点能量泄漏而导致的弯曲基带误差较大）。TRPMD方法产生的阻尼光谱与QCMD光谱一致，是迄今为止最便宜的方法。