Electrostatically embedded many-body expansion for large systems, with applications to water clusters
Electrostatically embedded many-body expansion for large systems, with applications to water clusters
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DOI：
10.1021/ct600253j
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发表时间：
2007-01-01
影响因子：
5.5
通讯作者：
Truhlar, Donald G.
中科院分区：
文献类型：
--
作者：
Dahlke, Erin E.;Truhlar, Donald G.
在量子化学中广泛使用背景分子电荷来结合分子或活性中心上的环境效应。在本文中，我们将这种做法与多体展开相结合。特别是，我们提出了静电嵌入的二体和三体展开来计算分子团簇的能量。该体系被分成多个片段，并在代表其他片段的静电势的点电荷场中计算片段的二聚体或三聚体。我们发现，与传统的两两相加近似相比，计入环境点电荷可以将一系列水原子团的静电嵌入成对加性(EE-PA)能量的误差降低10倍，对于静电嵌入三体(EE-3B)方法，对于六个四聚体和一个五聚体的九个不同理论水平的平均无符号误差仅为0.05kcal/mol，仅为平均无符号净相互作用能的0.4%。我们还测试了EE-PA和EE-3B方法对21个水分子簇的计算精度，发现相对于完整的MP2/Aug‘-cc-pVTZ计算，误差分别只有2.97和0.38千卡/摩尔，分别只有净相互作用能的1.5%和0.2%。这种方法与其他一些基于片段的方法相比具有优势，因为它不使用迭代方法来确定电荷，从而为大型集群提供了大量的节省。该方法便于适应各种电子结构方法和程序包，对大系统具有N-2或N-3计算标度，易于转化为O(N)方法，其线性允许方便的解析梯度。
The use of background molecular charge to incorporate environmental effects on a molecule or active site is widely employed in quantum chemistry. In the present article we employ this practice in conjunction with many-body expansions. In particular, we present electrostatically embedded two-body and three-body expansions for calculating the energies of molecular clusters. The system is divided into fragments, and dimers or trimers of fragments are calculated in a field of point charges representing the electrostatic potential of the other fragments. We find that including environmental point charges can lower the errors in the electrostatically embedded pairwise additive (EE-PA) energies for a series of water clusters by as much as a factor of 10 when compared to the traditional pairwise additive approximation and that for the electrostatically embedded three-body (EE-3B) method the average mean unsigned error over nine different levels of theory for a set of six tetramers and one pentamer is only 0.05 kcal/mol, which is only 0.4% of the mean unsigned net interaction energy. We also test the accuracy of the EE-PA and EE-3B methods for a cluster of 21 water molecules and find that the errors relative to a full MP2/aug'-cc-pVTZ calculation to be only 2.97 and 0.38 kcal/mol, respectively, which are only 1.5% and 0.2%, respectively, of the net interaction energy. This method offers the advantage over some other fragment-based methods in that it does not use an iterative method to determine the charges and thus provides substantial savings for large clusters. The method is convenient to adapt to a variety of electronic structure methods and program packages, it has N-2 or N-3 computational scaling for large systems (where N is the number of fragments), it is easily converted to an O(N) method, and its linearity allows for convenient analytic gradients.