Density-matrix-spectroscopic algorithm for excited-state adiabatic surfaces and molecular dynamics of a protonated Schiff base

Excited-state potentials of a short protonated Schiff base cation which ser ves as a model for the photoisomerization of retinal are computed by combin ing a semi-empirical ground-state adiabatic surface with excitation energie s obtained using the time-dependent coupled electronic oscillator (CEO) app roach. Excited-state molecular dynamic simulation of the in-plane motion of cis-C5H6NH2+ following impulsive optical excitation reveals a dominating 1 754 cm(-1) pi-conjugation mode. A new molecular dynamics algorithm is propo sed which resembles the Car-Parinello ground-state technique and is based o n the adiabatic propagation of the ground-state single-electron density mat rix and the collective electronic modes along the trajectory. (C) 1999 Amer ican Institute of Physics. [S0021-9606(99)30717-0].