ANT 2023: A program for adiabatic and nonadiabatic trajectories

ANT 2023 is a program for quasiclassical and semiclassical trajectories, both single-surface trajectories for which the Born-Oppenheimer approximation is valid and multi-surface calculations with electronic state changes, i.e., for electronically adiabatic and electronically nonadiabatic trajectories. There are several methods available for multisurface problems: surface hopping with or without time uncertainty and with or without decoherence, semiclassical Ehrenfest, self-consistent decay of mixing, and coherent switching with decay of mixing (CSDM). The potential surface for single-surface problems may be an analytic potential function supplied by the user, or one may use direct dynamics. To use the adiabatic representation (i.e., electronically adiabatic basis functions) for electronically nonadiabatic dynamics, the user may either provide the adiabatic surfaces and nonadiabatic couplings by direct dynamics, or the program may calculate them from diabatic surfaces and diabatic couplings, which are usually analytic. One can also use analytic fits to the surfaces and couplings to carry out calculations entirely in the diabatic representation. The curvature-driven approximation is available as an option for use with CSDM and trajectory surface hopping. The ANT 2023 program is especially recommended for calculations with analytic potential energy surfaces and couplings because of its high efficiency for such calculations.