title: Equation-of-motion coupled cluster method for the description of the high spin excited states.
abstract: The equation-of-motion (EOM) coupled cluster (CC) approach in the version applicable for the excitation energy(EE) calculations has been formulated for high spin components. The EE-EOM-CC scheme based on the restricted Hartree-Fock reference and standard amplitude equations as used in the Davidson diagonalization procedure yields the singlet states. The triplet and higher spin components require separate amplitude equations. In the case of quintets, the relevant equations are much simpler and easier to solve. Out of 26 diagrammatic terms contributing to the R1 and R2 singlet equations in the case of quintets, only R2 operator survives with 5 diagrammatic terms present. In addition all terms engaging three body elements of the similarity transformed Hamiltonian disappear. This indicates a substantial simplification of the theory. The implemented method has been applied to the pilot study of the excited states of the C2 molecule and quintet states of C and Si atoms.
authors.affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
authors.forename: Monika
authors.initials: M
authors.lastname: Musiał
authors.affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
authors.forename: Łukasz
authors.initials: Ł
authors.lastname: Lupa
authors.affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
authors.forename: Stanisław A
authors.initials: SA
authors.lastname: Kucharski