水团簇(H2O)n中多体作用强度与水分子间距的关系

使用高精度从头算方法(含基组重叠误差校正)计算了水团簇(H₂O)_n (n = 8, 10, 16, 20, 22, 24)中的所有二体、三体和四体作用能,分析了水团簇中的多体效应.研究表明,二体作用对体系总作用能的贡献高达70%以上,三体作用对总作用能的贡献可高达25%,四体作用在总作用能中所占比例不超过3%,五体及以上多体作用能在总作用能中所占比例更小,不超过0.5%.本文研究还表明,两个水分子间距小于0.68 nm的二体作用、三个和四个水分子中最近的两个水分子间距小于0.31 nm的三体和四体作用对体系总作用能的贡献高达99.4%.因此,以生物体系为对象的分子模拟方法应该具备准确地模拟两个水分子间距小于0.68 nm的二体作用、三个和四个水分子中最近的两个分子间距小于0.31 nm的三体和四体作用的能力.

Dependence of the Many-Body Interaction Strength in Water Clusters (H2O)n on the Water-Water Distance

The total interaction energies and two-, three-, and four-body interaction energies of water clusters (H₂O)_n (n = 8, 10, 16, 20, 22, 24) are obtained from MP2/aug-cc-pVTZ calculations including the basis set superposition error (BSSE) correction. The calculation results show that the two-body interaction energies contribute more than 70% to the total interaction energy, the three-body interaction energies contribute up to 25%, the four-body interaction energies sometimes contribute up to 3%, and other many-body interaction energies always contribute less than 0.5%. It is also found that about 99.4% of the total interaction energies can be reproduced when some special two-, three-, and four-body interactions are considered. These interactions are the two-body interactions where the distance between two water molecules is less than 0.68 nm, the three-body interactions where the nearest water-water distance among three water molecules is less than 0.31 nm, and the four-body interactions where the nearest water-water distance among four water molecules is less than 0.31 nm. Our investigation results suggest that a reliable method, aimed at modeling biosystems, should possess the ability to correctly simulate these special two-, three-, and four-body interactions.