Ab initio interpolated quantum dynamics on coupled electronic states with full configuration interaction wave functions

We present a new approach to first-principles molecular dynamics that combi nes a general and flexible interpolation method with ab initio evaluation o f the potential energy surface. This hybrid approach extends significantly the domain of applicability of ab initio molecular dynamics. Use of interpo lation significantly reduces the computational effort associated with the d ynamics over most of the time scale of interest, while regions where potent ial energy surfaces are difficult to interpolate, for example near conical intersections, are treated by direct solution of the electronic Schrodinger equation during the dynamics. We demonstrate the concept through applicati on to the nonadiabatic dynamics of collisional electronic quenching of Li(2 p). Full configuration interaction is used to describe the wave functions o f the ground and excited electronic states. The hybrid approach agrees well with full ab initio multiple spawning dynamics, while being more than an o rder of magnitude faster. (C) 1999 American Institute of Physics. [S0021-96 06(99)00103-8].