Symmetry-adapted-cluster configuration-interaction and equation-of-motion coupled-cluster studies of electronically excited states of copper tetrachloride and copper tetrabromide dianions

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• 作者：Masahiro Ehara^a ; ^b ; ^{ehara@ims.ac.jp} ; Piotr Piecuch^c ; ^{piecuch@chemistry.msu.edu} ; Jesse J. Lutz^c ; Jeffrey R. Gour^c ; ^d
• 关键词：Excited electronic states ; Open-shell transition metal complexes ; Scalar relativistic effects ; Symmetry-adapted-cluster configuration-interaction methodology ; Equation-of-motion coupled-cluster theory ; Active-space methods
• 刊名：Chemical Physics
• 出版年：2012
• 期刊代码：18_03010104
• 类别：ch
• 出版时间：3 May, 2012
• 卷：399
• 期：Complete
• 页码：94-110
• 文件大小：663 K

摘要

The valence excitation spectra of the copper tetrachloride and copper tetrabromide open-shell dianions, and , respectively, are investigated by a variety of symmetry-adapted-cluster configuration-interaction (SAC-CI) and equation-of-motion coupled-cluster (EOMCC) methods. The valence excited states of the and species that correspond to transitions from doubly occupied molecular orbitals (MOs) to a singly occupied MO (SOMO), for which experimental spectra are available, are examined with the ionized (IP) variants of the SAC-CI and EOMCC methods. The higher-energy excited states of and that correspond to transitions from SOMO to unoccupied MOs, which have not been characterized experimentally, are determined using the electron-attached (EA) SAC-CI and EOMCC approaches. An emphasis is placed on the scalar relativistic SAC-CI and EOMCC calculations based on the spin-free part of the second-order Douglass-Kroll-Hess Hamiltonian (DKH2) and on a comparison of the results of the IP and EA SAC-CI and EOMCC calculations with up to 2-hole-1-particle (2h-1p) and 2-particle-1-hole (2p-1h) excitations, referred to as the IP-SAC-CI SD-R and IP-EOMCCSD(2h-1p) methods in the IP case and EA-SAC-CI SD-R and EA-EOMCCSD(2p-1h) approaches in the EA case, with those obtained with the higher-level IP-EOMCC and EA-EOMCC theories with up to 3-hole-2-particle (3h-2p) and 3-particle-2-hole (3p-2h) excitations treated via active orbitals, abbreviated as IP-EOMCCSD(3h-2p) and EA-EOMCCSD(3p-2h), respectively, as well as with the available experimental data. It is demonstrated that all of the employed DKH2-based IP-SAC-CI and IP-EOMCC methods offer a reliable description of the valence excited states of the and complexes that correspond to transitions from doubly occupied MOs to SOMO, accurately reproducing the observed UV-vis absorption spectra in both peak positions and intensities, which enables a rigorous assignment of the observed strong bands and weaker shoulder transitions. It is also shown that the scalar relativistic effects have a non-negligible effect on the excitation energies, on the order of 0.1-0.2 eV, and a substantial effect on the calculated ground-state geometries, particularly in the case of the complex and the Cu-Br bond length, although the effect of relativity on the oscillator strengths is generally very small.