Validity of time-dependent self-consistent-field (TDSCF) approximations for unimolecular dynamics: A test for photodissociation of the Xe–HI cluster

The photodissociation dynamics of a collinear model of the van der Waals cluster Xe–HI is used as a testing ground for time-dependent self-consistent field (TDSCF) approximations. In this study, the quantum-mechanical TDSCF and a combined classical/quantal TDSCF (in which the light atom is treated quantum mechanically, the heavy atoms are treated classically) are compared to numerically exact wave packet calculations. Very good agreement is found between the TDSCF approximations and the exact result over the entire subpicosecond time duration of the process. In particular, all the properties related to the quantal degree of freedom in the combined quantal/classical TDSCF method reproduce almost perfectly the exact results. However, the classical mode in the hybrid approximation is somewhat less well described due to insufficient representation of energy transfer between the modes. The conclusions are very promising as to the applicability of TDSCF methods, in particular the hybrid quantal/classical scheme to more complex systems in which only a few degrees of freedom can be treated quantum mechanically.