Department of Earth Sciences, UCL, Gower St., London WC1E 6BT, United Kingdom.
J Chem Phys. 2010 Jul 28;133(4):044103. doi: 10.1063/1.3466919.
We show how the path-integral formulation of quantum statistical mechanics can be used to construct practical ab initio techniques for computing the chemical potential of molecules adsorbed on surfaces, with full inclusion of quantum nuclear effects. The techniques we describe are based on the computation of the potential of mean force on a chosen molecule and generalize the techniques developed recently for classical nuclei. We present practical calculations based on density functional theory with a generalized-gradient exchange-correlation functional for the case of H(2)O on the MgO (001) surface at low coverage. We note that the very high vibrational frequencies of the H(2)O molecule would normally require very large numbers of time slices (beads) in path-integral calculations, but we show that this requirement can be dramatically reduced by employing the idea of thermodynamic integration with respect to the number of beads. The validity and correctness of our path-integral calculations on the H(2)O/MgO(001) system are demonstrated by supporting calculations on a set of simple model systems for which quantum contributions to the free energy are known exactly from analytic arguments.
我们展示了如何将量子统计力学的路径积分公式用于构建用于计算吸附在表面上的分子化学势的实用从头计算技术，其中包括完全包含量子核效应。我们描述的技术基于对所选分子的平均力势的计算，并推广了最近为经典核开发的技术。我们基于密度泛函理论提出了实际计算，使用广义梯度交换相关泛函对低覆盖度下 H(2)O 在 MgO(001)表面的情况进行了计算。我们注意到，H(2)O 分子的非常高的振动频率通常需要在路径积分计算中使用大量的时间切片（珠子），但我们表明，通过采用对珠子数量进行热力学积分的想法，可以大大减少这种需求。我们对 H(2)O/MgO(001)系统的路径积分计算的有效性和正确性通过对一组简单模型系统的支持计算得到了证明，这些系统的自由能的量子贡献可以通过解析论证精确地计算出来。
