Spin-orbit coupling with approximate equation-of-motion coupled-cluster method for ionization potential and electron attachment.
Spin-orbit coupling with approximate equation-of-motion coupled-cluster method for ionization potential and electron attachment.
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DOI：
10.1063/1.4964859
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发表时间：
2016-10
期刊：
影响因子：
--
通讯作者：
Zhanli Cao;Fan Wang;Mingli Yang
中科院分区：
文献类型：
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作者：
Zhanli Cao;Fan Wang;Mingli Yang
为了减少计算量，提出了在自洽场（SCF）计算中考虑自旋轨道耦合（SOC）的电离势（IP）和电子亲合势（EA）的运动方程耦合团簇（EOM-CC）方法中计算团簇振幅的各种近似方法.我们的研究结果表明，EOM-CC的基础上集群振幅近似方法CCSD-1，其中的单一方程是相同的CCSD和双振幅近似MP2，能够提供合理的IP和EA相比，当SOC不存在CCSD的结果。这是一种经济的方法来计算IP和EA，并且不像CC 2那样对强相关性敏感。当考虑SOC时，近似方法CCSD-3采用与SOC-CCSD相同的一元方程和标量-相对论CCSD的二元方程，得到了与CCSD最接近的IPs和EAs。然而，CC 2的EOM-CC SO分裂与CCSD的SO分裂基本一致，而CCSD-1和CCSD-3的SO分裂精度较差。这表明需要平衡处理SOC对单激励振幅和双激励振幅的影响，以实现可靠的SO分裂。
Various approximate approaches to calculate cluster amplitudes in equation-of-motion coupled-cluster (EOM-CC) approaches for ionization potentials (IP) and electron affinities (EA) with spin-orbit coupling (SOC) included in post self-consistent field (SCF) calculations are proposed to reduce computational effort. Our results indicate that EOM-CC based on cluster amplitudes from the approximate method CCSD-1, where the singles equation is the same as that in CCSD and the doubles amplitudes are approximated with MP2, is able to provide reasonable IPs and EAs when SOC is not present compared with CCSD results. It is an economical approach for calculating IPs and EAs and is not as sensitive to strong correlation as CC2. When SOC is included, the approximate method CCSD-3, where the same singles equation as that in SOC-CCSD is used and the doubles equation of scalar-relativistic CCSD is employed, gives rise to IPs and EAs that are in closest agreement with those of CCSD. However, SO splitting with EOM-CC from CC2 generally agrees best with that with CCSD, while that of CCSD-1 and CCSD-3 is less accurate. This indicates that a balanced treatment of SOC effects on both single and double excitation amplitudes is required to achieve reliable SO splitting.