Villaume Sébastien, Daniel Chantal, Strich Alain, Perera S Ajith, Bartlett Rodney J
Laboratoire de Chimie Quantique UMR 7551 CNRS, Universite Louis Pasteur, 4 rue Blaise Pascal, 67000 Strasbourg, France.
J Chem Phys. 2005 Jan 22;122(4):44313. doi: 10.1063/1.1834897.
The electronic structure of NiCH(2) (+), representative of transition metal carbene ions, is investigated by means of several methods of quantum chemistry. The relative stabilities of the four low-lying doublet electronic states ((2)A(1), (2)A(2), (2)B(1), and (2)B(2)) are determined at the coupled cluster singles and doubles level (CCSD) and triples level [CCSD(T) and CCSDT-3] with both a Hartree-Fock and density functional theory (Kohn-Sham) reference. The equation-of-motion coupled cluster for treatment of excited states in singles and doubles approximation (EOM-CCSD) is used to characterize the transition energies from the (2)A(1) electronic ground state to the low-lying doublet excited states. The (2)A(2) and (2)B(1) states are nearly degenerate, found to be separated by 940 cm(-1) at the EOM-CCSD level, in agreement with the CASSCF energy ordering. The (2)B(2) state is calculated to be higher in energy by more than 1.0 eV. The spin purity of the low-lying doublet and quadruplet states described by CCSD calculations based on the unrestricted open-shell Hartree-Fock reference is discussed.
采用多种量子化学方法研究了作为过渡金属卡宾离子代表的NiCH(2)(+)的电子结构。在耦合簇单双激发水平（CCSD）和三激发水平[CCSD(T)和CCSDT-3]下，以Hartree-Fock和密度泛函理论（Kohn-Sham）为参考，确定了四个低能双峰电子态（(2)A(1)、(2)A(2)、(2)B(1)和(2)B(2)）的相对稳定性。采用运动方程耦合簇单双激发近似（EOM-CCSD）来表征从(2)A(1)基态到低能双峰激发态的跃迁能量。(2)A(2)和(2)B(1)态几乎简并，在EOM-CCSD水平下发现它们的能量间隔为940 cm(-1)，这与CASSCF能量排序一致。计算得出(2)B(2)态的能量高出1.0 eV以上。讨论了基于无限制开壳Hartree-Fock参考的CCSD计算所描述的低能双峰和四峰态的自旋纯度。
