关于表面模型上吸附分子的自由能计算

freeEnergy

各位量化专家，sob老师帮我看看：
  最近在做氧还原的计算，对反应自由能变的计算上有些问题，文献上是这样说的：
  The difference between the free energies of the initial and final states is determined as dG = dE+dZPE-TdS+dGU, where dE corresponds to the reaction energy calculated using DFT. ZPE is the zero-point energy, S is the entropy, and dGU =- eU (e is the unit positivecharge and U is the electrode potential with respect to standard hydrogen electrode).
The ZPE corrections were obtained from the vibrational frequencies calculated by treating 3N degrees of freedom of adsorbates. The values of the corrections are shown in Table 1. The phonon contribution of the OG sheet was not included as this contribution is expected to be similar in all the cases studied here and cancelled out in the calculation of energy differences.
The effect of the entropies ofadsorbates has been shown to be small, [27] and therefore,neglected in the present study, the entropy contributions of gas phase molecules were taken from the NIST database .
吸附模型是氧化石墨烯OG表面吸附含氧分子，对里面的反应自由能变的计算，但是第二段里面 零点振动能对自由能的修正中有疑惑，为什么只需要处理吸附分子的三维自由度呢，这个要怎么计算，这个和晶格振动可以分开算么？
  

freeEnergy

有一个比较大的问题是，考虑一个分子吸附在固体表面时对其做振动分析，所得到的零点振动能就是指吸附分子的么，不用考虑固体的振动，是么？