Vibronic transitions from coupled-cluster response theory: Theory and application to HSiF and H2O

A scheme for calculating the vibrational structure of electronic spectra using coupled-cluster response theory is proposed. To calculate the vibrational structure of electronic transitions, the optimized geometries of the two electronic states, the molecular Hessians, the dipole transition moment and (for vibrationally induced transitions) the geometrical gradient of the dipole transition moment are used in conjunction with a recently developed method for the evaluation of Franck-Condon factors of multidimensional harmonic oscillators. Allowed and vibrationally induced transitions are both described. In this pilot implementation, the required geometrical derivatives are calculated by an automated finite-difference method. The scheme is applied to the 1 (1)A"<--1 (1)A' transition of monofluorosilylene (HSiF) and the vibrationally induced 1 (1)A(2)<--1 (1)A(1) transition of water. (C) 2002 American Institute of Physics