Semiclassical simulations of the spectra of anharmonic molecules; problems and alternatives

Abstract

Several semiclassical approaches for calculations of the absorption lineshape of anharmonic systems are examined. The recently developed semiclassical Green's function (SGF) method is found to give excellent results. The Gaussian wavepacket method does not appear to produce the exact quantization when the anharmonicity of the system increases. It is argued that the exact time-dependent propagator should include information from trajectories at all energies. Thus it might be preferable to use the SGF method which requires one to run trajectories only at the relevant energy range.