AuX（X=O，S）低电子态的理论研究

摘要

Multireference approaches have commonly been employed to calculate low-lying states of open-shel molecules with spin-orbit coupling (SOC), such as for AuO and AuS. However, by choosing a proper reference state, the equation-of-motion coupled-cluster approach (EOM-CC) can also be used to calculate some low-lying states of these molecules. Furthermore, the EOM-CC approach is a single-reference method and, therefore, more easily employed than multireference approaches. In this work, low-lying states of AuO and AuS are investigated based on a recently developed EOM-CC approach for ionization potentials (EOMIP-CC) with SOC at the CCSD level, using the corresponding anions as reference. The contribution of triples with EOMIP-CC is estimated by comparing results of EOMIP-CCSD and EOMIP-CCSDT at a scalar relativistic level. In addition, compared with the EOMIP-CCSDT results, errors by UCCSD(T) can reach 0.1-0.15 eV when spin contamination is significant and the norm of T1 is sizeable. When SOC is present, bond lengths and harmonic frequencies obtained with EOMIP-CCSD for the investigated states are in reasonable agreement with experimental data. Furthermore, ionization energies corresponding to the high-lying 2Δ3/2, 2Σ+1/2, and 2Π1/2 states are overestimated by EOMIP-SOC-CCSD, but results for the other low-lying states agree wel with the experimental data, with an error of approximately 0.2 eV. These results indicate that the single-reference EOMIP-CCSD method with SOC is able to provide a reasonable description of low-lying states of AuO and AuS.%通常要用多参考态方法才能合理处理需考虑旋轨耦合(SOC)效应的开壳层分子如AuO和AuS的低电子态.事实上，通过选取合适的参考态，采用运动方程耦合簇方法(EOM-CC)也能计算这些分子的一些低电子态，而且EOM-CC方法是单参考态方法，使用起来比多参考态方法更加简单.本文采用最近发展的含旋轨耦合的EOM-CC计算电离能的方法(EOMIP-CC)，选取对应的负离子为参考态，在CCSD级别上计算了AuO和AuS低电子态的性质.在不考虑旋轨耦合时，通过比较EOMIP-CCSD和EOMIP-CCSDT的结果考察EOMIP-CCSD的精度.此外，与EOMIP-CCSDT结果相比，如果自旋污染较为显著而且T1的模较大时， UCCSD(T)方法对能量最低的某一特定对称性的电子态的所对应的电离能误差约为0.1-0.15 eV.在考虑了旋轨耦合效应后，我们的方法得到的键长和振动频率与实验值吻合较好.另一方面，虽然EOMIP-SOC-CCSD高估了能量较高的2Δ3/2态、2Σ+1/2态和2Π1/2态的能量，但是对于其它能量更低的电子态，它们的能量与已有实验值误差在0.2 eV左右.这显示我们所用的含SOC的EOMIP-CCSD方法对原本需要用多参考态方法才能处理的AuO和AuS低电子态能给出可靠的结果.