title: Calculation of Dipole Transition Matrix Elements and Expectation Values by Vibrational Coupled Cluster Method.
abstract: An effective operator approach based on the coupled cluster method is described and applied to calculate vibrational expectation values and absolute transition matrix elements. Coupled cluster linear response theory (CCLRT) is used to calculate excited states. The convergence pattern of these properties with the rank of the excitation operator is studied. The method is applied to a water molecule. Arponen-type double similarity transformation in extended coupled cluster (ECCM) framework is also used to generate an effective operator, and the convergence pattern of these properties is compared to the normal coupled cluster (NCCM) approach. It is found that the coupled cluster method provides an accurate description of these quantities for low lying vibrational excited states. The ECCM provides a significant improvement for the calculation of the transition matrix elements.
authors.affiliation: Physical Chemistry Division, National Chemical Laboratory, Pune 411008, India.|School of Chemistry, University of Hyderabad, Hyderabad 500046, India.
authors.forename: Subrata
authors.initials: S
authors.lastname: Banik
authors.affiliation: Physical Chemistry Division, National Chemical Laboratory, Pune 411008, India.|School of Chemistry, University of Hyderabad, Hyderabad 500046, India.
authors.forename: Sourav
authors.initials: S
authors.lastname: Pal
authors.affiliation: Physical Chemistry Division, National Chemical Laboratory, Pune 411008, India.|School of Chemistry, University of Hyderabad, Hyderabad 500046, India.
authors.forename: M Durga
authors.initials: MD
authors.lastname: Prasad