Direct quantum dynamics using variational multi-configuration Gaussian wavepackets

Direct quantum dynamics using variational multi-configuration Gaussian wavepackets is intended to treat quantum effects in the photochemistry of large molecules. It uses on-the-fly quantum chemical calculation of the potential energy and its derivatives rather than fitted surfaces. Intermediate results are stored in a database to avoid repeated quantum chemical computations. The use of Cartesian coordinates is discussed and a comparison is made between free and constrained approaches with respect to rotation. This method is then applied to the computation of the photodissociation spectrum of nitrosyl chloride (NOCl) - a benchmark to be compared to published full quantum calculations.

We present a new direct dynamics implementation of the variational multi-configuration Gaussian wavepacket method. The photodissociation spectrum of NOCl is obtained from an initial wavepacket expressed as a function of Cartesian coordinates constrained to separate the rotation. A complete active space self-consistent field potential energy surface is locally calculated on-the-fly.