Hillers-Bendtsen Andreas Erbs, Høyer Nicolai Machholdt, Kjeldal Frederik Ørsted, Mikkelsen Kurt V, Olsen Jeppe, Jørgensen Poul
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK 2100 Copenhagen Ø, Denmark.
Department of Chemistry, Aarhus University, Langelandsgade 140, DK 8000 Aarhus C, Denmark.
J Chem Phys. 2022 Jul 14;157(2):024108. doi: 10.1063/5.0082585.
We have extended cluster perturbation (CP) theory to comprehend the calculation of first order properties (FOPs). We have determined CP FOP series where FOPs are determined as a first energy derivative and also where the FOPs are determined as a generalized expectation value of the external perturbation operator over the coupled cluster state and its biorthonormal multiplier state. For S(D) orbital excitation spaces, we find that the CP series for FOPs that are determined as a first derivative, in general, in second order have errors of a few percent in the singles and doubles correlation contribution relative to the targeted coupled cluster (CC) results. For a SD(T) orbital excitation space, we find that the CP series for FOPs determined as a generalized expectation value in second order have errors of about ten percent in the triples correlation contribution relative to the targeted CC results. These second order models, therefore, constitute viable alternatives for determining high quality FOPs.
我们已经扩展了团簇微扰（CP）理论，以涵盖一阶性质（FOPs）的计算。我们确定了CP FOP系列，其中FOPs被确定为一阶能量导数，并且FOPs也被确定为外部微扰算符在耦合簇态及其双正交乘子态上的广义期望值。对于S(D)轨道激发空间，我们发现，对于被确定为一阶导数的FOPs的CP系列，一般来说，在二阶时，单重和双重关联贡献相对于目标耦合簇（CC）结果有百分之几的误差。对于SD(T)轨道激发空间，我们发现，对于被确定为广义期望值的FOPs的CP系列，在二阶时，三重关联贡献相对于目标CC结果有大约百分之十的误差。因此，这些二阶模型构成了确定高质量FOPs的可行替代方案。
