Ab initio molecular dynamics with equation-of-motion coupled-cluster theory: electronic absorption spectrum of ethylene

The equation-of-motion coupled-cluster (EOM-CCSD) method has been combined with the full multiple-spawning (FMS) method to include dynamic electron correlation effects in ab initio excited state dynamics. We use a quasi-diabatic scheme to follow adiabatic states, demanding smooth variation of the EOM-CCSD energy and oscillator strength. The potential energy surfaces computed 'on-the-fly' are used in the simulation of electronic absorption spectra. We compute absorption spectra of ethylene for the Rydberg pi --> 3s and valence pi --> pi* states, and compare directly to experimental results. Good agreement is obtained in the 50000-70000 cm(-1) range. (C) 2003 Elsevier Science B.V. All rights reserved.