title: Efficiency of perturbation-selection and its orbital dependence in the SAC-CI calculations for valence excitations of medium-size molecules.
abstract: The efficiency and accuracy of the perturbation-selection used in the symmetry-adapted cluster-configuration interaction (SAC-CI) calculations are investigated for several low-lying valence excited states of 21 medium-size molecules, including typical chromophores with heterocyclic macrocycles (free-base porphine, coumarin, indole, and BODIPY), nucleobases, amino acids (tyrosine and tryptophan), polycyclic aromatic hydrocarbons, and organometallics (ferrocene and Re(bpy)(CO)4+1). Benchmark SAC-CI calculations with up to 110 million operators are performed. The efficiency of the perturbation-selection depends on the molecular orbitals (MOs); therefore, the canonical MO and localized MO (LMO) obtained by Pipek-Mezey's method are examined. Except for the highly symmetric molecules, using LMOs improves the efficiency and accuracy of the perturbation-selection. With using LMOs and perturbation-selection, sufficiently reliable results can be obtained in less than 10% of the computational costs required for the full-dimensional calculations. The perturbation-selection with LMOs is suggested to be a promising method for excited states in larger molecular systems.
authors.affiliation: Institute for Molecular Science and Research Center for Computational Science, 38 Nishigo-naka, Myodaiji, Okazaki, 444-8585, Japan.; Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University Katsura, Kyoto, 615-8520, Japan.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Fukuda
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ehara
keywords: SAC-CI; excited state; localized molecular orbital