Department of Basic Courses, Tangshan College, Tangshan 063000, China.
J Chem Phys. 2012 Apr 28;136(16):164313. doi: 10.1063/1.4705371.
The quantitative estimation of the total interaction energy of a molecular system containing hydrogen bonds (H bonds) depends largely on how to identify H bonding. The conventional geometric criteria of H bonding are simple and convenient in application, but a certain amount of non-H bonding cases are also identified as H bonding. In order to investigate the wrong identification, we carry out a systematic calculation on the interaction energy of two water molecules at various orientation angles and distances using ab initio molecular dynamics method with the dispersion correction for the Becke-Lee-Yang-Parr (BLYP) functionals. It is shown that, at many orientation angles and distances, the interaction energies of the two water molecules exceed the energy criterion of the H bond, but they are still identified as H-bonded by the conventional "distance-angle" criteria. It is found that in these non-H bonding cases the wrong identification is mainly caused by short-range interaction between the two neighbouring water molecules. We thus propose that, in addition to the conventional distance and angle criteria of H bonding, the distance d(H···H) between the two neighbouring hydrogen atoms of the two water molecules should also be taken as a criterion, and the distance r(O···H) between the hydrogen atom of the H-bond donor molecule and the oxygen atom of the acceptor molecule should be restricted by a lower limit. When d(H···H) and r(O···H) are small (e.g., d(H···H) < 2.0 Å and r(O···H) < 1.62 Å), the repulsion between the two neighbouring atoms increases the total energy of the two water molecules dramatically and apparently weakens the binding of the water dimer. A statistical analysis and comparison of the numbers of the H bonds identified by using different criteria have been conducted on a Car-Parrinello ab initio molecular dynamics simulation with dispersion correction for a system of 64 water molecules at near-ambient temperature. They show that the majority of the H-bonds counted by using the conventional criteria combined with the d(H···H) criterion and the restriction of r(O···H) match what is identified by the binding energy criteria (e.g., E ≤ -10 kJ/mol), while some of them still have a binding energy that exceeds the energy criterion, indicating that the complicated quantum effects in H bonding can only be described by the three geometric parameters to a certain extent.
氢键（H 键）的分子系统总相互作用能的定量估计在很大程度上取决于如何识别 H 键。传统的 H 键几何标准在应用中简单方便，但也有一定数量的非 H 键情况被错误地识别为 H 键。为了研究这种错误识别，我们使用含色散修正的 Becke-Lee-Yang-Parr（BLYP）泛函的从头算分子动力学方法，对两个水分子在不同取向角度和距离下的相互作用能进行了系统计算。结果表明，在许多取向角度和距离下，两个水分子的相互作用能超过了 H 键的能量标准，但它们仍被传统的“距离-角度”标准识别为 H 键。我们发现，在这些非 H 键的情况下，错误识别主要是由两个相邻水分子之间的短程相互作用引起的。因此，我们提出，除了传统的 H 键距离和角度标准外，还应将两个水分子的两个相邻氢原子之间的距离 d(H···H)作为标准，并且氢键供体分子的氢原子与受体分子的氧原子之间的距离 r(O···H)应受到下限的限制。当 d(H···H)和 r(O···H)较小时（例如，d(H···H) < 2.0 Å，r(O···H) < 1.62 Å），两个相邻原子之间的排斥作用会显著增加两个水分子的总能量，并明显削弱水二聚体的结合。在近环境温度下，对带有色散修正的 64 个水分子体系进行了 Car-Parrinello 从头算分子动力学模拟，并对使用不同标准识别的氢键数量进行了统计分析和比较。结果表明，使用传统标准结合 d(H···H)标准和 r(O···H)限制标准计算的大多数氢键与结合能标准（例如，E ≤ -10 kJ/mol）识别的氢键相匹配，而其中一些氢键的结合能仍然超过能量标准，这表明氢键中的复杂量子效应在一定程度上只能用这三个几何参数来描述。
