title: Block diagonalization of the equation-of-motion coupled cluster effective Hamiltonian: treatment of diabatic potential constants and triple excitations.
abstract: We present a diabatization method applicable to spectroscopic studies based on Equation-of-Motion Coupled Cluster (EOM-CC) energies and biorthogonal wavefunctions that uses the Block Diagonalization (BD) approaches of Cederbaum et al. [L. S. Cederbaum, J. Schirmer, and H. D. Meyer, J. Phys. A: Math. Gen. 22, 2427 (1989)] and Domcke et al. [W. Domcke and C. Woywod, Chem. Phys. Lett. 216, 362 (1993); W. Domcke, C. Woywod, and M. Stengle, Chem. Phys. Lett. 226, 257 (1994)]. The method gives excellent agreement with coupling constants calculated using the analytic gradient approach of Ichino et al. [T. Ichino, J. Gauss, and J. F. Stanton, J. Chem. Phys. 130, 174105 (2009)]. While the BD method is a finite difference approach, it can be applied at any geometry, can generate (pointwise) diabatic potential energy surfaces, and can be used with EOM wavefunctions that include triple (or higher) excitations. The method is applied to several model systems and its sensitivity to orbital choice, excitation space, and projection space is explored.
authors.affiliation: Department of Chemistry, Harvey Mudd College, 241 Platt Blvd., Claremont, California 91711, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cave
authors.affiliation: Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Ave., Austin, Texas 78712, USA.
authors.forename: John F
authors.initials: JF
authors.lastname: Stanton