Dg. Evans et Rd. Coalson, RELAXATION THEORY FOR CURVE-CROSSING CORRECTIONS TO ELECTRONIC ABSORPTION-LINE SHAPES IN CONDENSED PHASES, The Journal of chemical physics, 99(9), 1993, pp. 6264-6277
A quantum mechanical relaxation theory is developed to enable approxim
ate computation o electronic absorption line shapes of condensed phase
systems where nonadiabatic coupling effects are important. At the sim
plest level, these computations require a time kernel (termed a memory
kernel) which can be obtained from a sequence of wave packet propagat
ions, each carried out on a single Born-Oppenheimer potential surface.
Complications associated with the need to evolve wave packets on seve
ral nonadiabatically coupled surfaces are thereby avoided. Moreover, f
or many condensed phase problems the memory kernel can be computed via
semiclassical techniques which rely on classical trajectories and sim
ple Monte Carlo methods. The promise of the theory is demonstrated by
numerical applications to the spectroscopic spin boson model [R. D. Co
alson, J. Chem. Phys. 86, 995 (1987)], a nontrivial multimode model of
electronic absorption lineshapes involving two nonadiabatically coupl
ed excited state surfaces. The relevant quantum dynamics for the spect
roscopic spin boson model can be computed exactly via path integration
techniques. In this way, the accuracy of the proposed relaxation theo
ry can be benchmarked, and the applicability of various semiclassical
prescriptions for computing the memory kernel ascertained.