Fedorov Dmitri G, Kitaura Kazuo
National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki, Japan 305-6568.
J Chem Phys. 2005 Oct 1;123(13):134103. doi: 10.1063/1.2007588.
The fragment molecular-orbital (FMO) method was combined with the single-reference coupled-cluster (CC) theory. The developed method (FMO-CC) was applied at the CCSD and CCSD(T) levels of theory, for the cc-pVnZ family of basis sets (n=D,T,Q) to water clusters and glycine oligomers (up to 32 molecules/residues using as large basis sets as possible for the given system). The two- and three-body FMO-CC results are discussed at length, with emphasis on the basis-set dependence and three-body effects. Two- and three-body approximations based on interfragment distances were developed and the values appropriate for their accurate application carefully determined. The error in recovering the correlation energy was several millihartree for the two-body FMO-CC method and in the submillihartree range for the three-body FMO-CC method. In the largest calculations, we were able to perform the CCSD(T) calculations of (H2O)32 with the cc-pVQZ basis set (3680 basis functions) and (GLY)32 with the cc-VDZ basis set (712 correlated electrons). FMO-CC was parallelized using the upper level of the two-layer parallelization scheme. The computational scaling of the two-body FMO-CC method was demonstrated to be nearly linear. As an example of timings, CCSD(T) calculations of (H2O)32 with cc-pVDZ took 13 min on an eight node 3.2-GHz Pentium4 cluster.
片段分子轨道（FMO）方法与单参考耦合簇（CC）理论相结合。所开发的方法（FMO-CC）应用于CCSD和CCSD(T)理论水平，针对cc-pVnZ基组家族（n = D、T、Q）用于水簇和甘氨酸寡聚物（对于给定系统，使用尽可能大的基组，最多32个分子/残基）。详细讨论了两体和三体FMO-CC结果，重点是基组依赖性和三体效应。基于片段间距离开发了两体和三体近似，并仔细确定了适用于其精确应用的值。对于两体FMO-CC方法，恢复相关能的误差为几毫哈特里，对于三体FMO-CC方法，误差在亚毫哈特里范围内。在最大规模的计算中，我们能够使用cc-pVQZ基组（3680个基函数）对(H2O)32进行CCSD(T)计算，并使用cc-VDZ基组（712个相关电子）对(GLY)32进行CCSD(T)计算。FMO-CC使用两层并行化方案的上层进行并行化。两体FMO-CC方法的计算缩放被证明几乎是线性的。作为计时示例，在一个八节点3.2 GHz奔腾4集群上，使用cc-pVDZ对(H2O)32进行CCSD(T)计算需要13分钟。
