Alternative ansätze in single reference coupled-cluster theory. III. A critical analysis of different methods
Alternative ansätze in single reference coupled-cluster theory. III. A critical analysis of different methods
复制标题
单参考耦合簇理论中的替代分析 III。
DOI：
10.1063/1.469641
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发表时间：
1995
影响因子：
4.4
通讯作者：
R. Bartlett
中科院分区：
文献类型：
--
作者：
P. Szalay;M. Nooijen;R. Bartlett
如果量子化学方法要提供一种广泛适用的方法，有几个重要的形式要求应该得到满足。本文考虑了各种位势指数分析，并评估了它们在不同期望下的性质，特别是对称广义Hellmann-Feynman定理的满足性、方法在不截断极限下的正确性和方程的有限性。分析方法有标准耦合簇(CC)、期望值(XCC)、对称期望值(SXCC)、么正(UCC)和扩展的(ECC)耦合簇方法。ECC满足大多数特定的理想数据，但它不满足对称的GHF定理。证明了SXCC是ECC的对称化近似，它确实满足对称GHF定理，但SXCC在不截断极限下是不精确的。提出了一种新的可选的强连通SC-XCC，它满足除方程不可终止性外的所有要求。考虑到所有高级CC方法都需要近似，能量泛函方程和定常方程的非有限性可能不是一个主要的限制。
There are several important formal requirements that should be satisfied if a quantum chemical method is to offer a widely applicable approach. This paper considers a variety of potential exponential ansatze, and assesses their attributes pertaining to different desiderata, in particular satisfaction of a symmetric generalized Hellmann–Feynman theorem, exactness of the method in the untruncated limit and finiteness of the equations. The ansatze are the standard coupled‐cluster (CC); the expectation value (XCC); symmetric expectation value (SXCC); unitary (UCC); and the extended (ECC) coupled‐cluster approaches. ECC satisfies most specified desiderata, but it does not satisfy a symmetric GHF theorem. SXCC is shown to be a symmetrized approximation to ECC, which does satisfy a symmetric GHF theorem, but SXCC is not exact in the untruncated limit. A new alternative ansatz, strongly connected SC‐XCC is proposed which satisfies all desiderata except that the equations are nonterminating. Considering the necessity of approximation for all high level alternative CC methods, the nonfiniteness of the energy functional and stationary equations might not be a major limitation.