从DFT液态水中提取的水单体和二聚体的耦合簇基准：单体变形的重要性
Coupled cluster benchmarks of water monomers and dimers extracted from DFT liquid water: the importance of monomer deformations
摘要：
为了理解流行的密度泛函理论（DFT）交换相关（xc）泛函在模拟液态水中的性能，从液态水的PBE模拟中提取水单体和二聚体，并使用具有单激发和双激发的耦合簇加上对连接三元组的微扰校正[CCSD（T）]进行检查。CCSD（T）揭示，与两个气相相平衡水单体相比，大多数二聚体是未结合的，这主要是因为液体中的单体具有扭曲的几何形状。测试的三个xc功能，PBE和BLYP系统地低估了单体变形的成本，因此预测二聚体内单体之间的解离能太大。这与这些官能团在气相中对于平衡水二聚体和其他小水簇的表现形成鲜明对比，这些小水簇仅具有适度变形的单体。PBE 0很好地再现了CCSD（T）单体变形能，因此比PBE和BLYP更准确地再现了二聚体解离能。虽然这项研究是有限的水单体和二聚体，这里报道的结果可能会提供一个解释的过度结构的径向分布函数，经常观察到的BLYP和PBE模拟的液态水和相关的水在其他阶段和其他相关的分子液体。
英文摘要：
To understand the performance of popular density-functional theory (DFT) exchange-correlation (xc) functionals in simulations of liquid water, water monomers and dimers were extracted from a PBE simulation of liquid water and examined with coupled cluster with single and double excitations plus a perturbative correction for connected triples [CCSD(T)]. CCSD(T) reveals that most of the dimers are unbound compared to two gas phase equilibrium water monomers, largely because monomers within the liquid have distorted geometries. Of the three xc functionals tested, PBE and BLYP systematically underestimate the cost of the monomer deformations and consequently predict too large dissociation energies between monomers within the dimers. This is in marked contrast to how these functionals perform for an equilibrium water dimer and other small water clusters in the gas phase, which only have moderately deformed monomers. PBE0 reproduces the CCSD(T) monomer deformation energies very well and consequently the dimer dissociation energies much more accurately than PBE and BLYP. Although this study is limited to water monomers and dimers, the results reported here may provide an explanation for the overstructured radial distribution functions routinely observed in BLYP and PBE simulations of liquid water and are of relevance to water in other phases and to other associated molecular liquids.
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