Finite temperature vibronic spectra of harmonic surfaces: a time-dependent coupled cluster approach

Abstract

An algorithm to compute vibronic spectra of harmonic surfaces including Dushinsky rotation and Hertzberg–Teller terms is described. The method, inspired by thermo field dynamics, maps the thermal density matrix onto the vacuum state and uses the time-dependent coupled cluster ansatz to propagate it in time. In the Franck–Condon approximation where the dipole matrix elements are taken to be constants, this reduces to the auto correlation function of the new vacuum. In the Hertzberg–Teller approximation, the full time evolution operator is needed. This too is governed by a closed set of equations. The theoretical development is presented along with an application to anthracene.

Keywords:

• finite temperature
• electronic absorption and florescence
• vibronic spectra
• time-dependent couple cluster method

Acknowledgements

It is a pleasure and privilege to dedicate this work to Prof. Sourav Pal on the occasion of his 60th birthday. M. Durga Prasad would like to thank Prof. V. Srinivasan for several instructive discussions on thermo field dynamics. Ch. Sridhar Reddy acknowledges a sustaining fellowship from UGC.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Financial support from DST (HPCF, PURSE, IYC and FIST programmes at the University of Hyderabad) and UGC (CAS and UPE programmes) is gratefully acknowledged.