A new method for numerical flux calculations in quantum molecular dynamics

The flux of an evolving wavepacket is the definite time integral of its probability current density. A new method for calculating the flux, based on a Chebychev polynomial expansion of the quantum evolution operator is presented. The central point of the development is that the time integration of the current density is performed analytically, resulting in a scheme which eliminates additional numerical errors. Using this method, one benefits from both the time-dependent and time-independent frameworks of the dynamics. Furthermore, the method requires only a small modification to the existing Chebychev polynomial evolution code. Examples of performance and accuracy and an application to the calculation of recombinative desorption probabilities of N2 on Re are shown and discussed.