VESH: A vertical energy surface hopping procedure for determining stable isomers of polyatomic molecular systems

We describe a heuristic algorithmic procedure by which a large number of po ints of minimal energy in configuration space of a polyatomic molecular sys tem (isomers) can be determined. Making use of the intrinsic electronic str ucture energy scheme of the molecular system, the procedure is initiated fr om an arbitrary starting configuration and progresses via successive vertic al spin, and/or charge state shifts with interposed optimization steps. In this systematic way, a great manifold of stable isomers not only on the gro und state potential energy surface but also on excited spin and charge stat e surfaces can be located. The efficiency and computational practicability of the procedure has been tested on various examples. In these cases, the g lobal minima have been found. Results for singlet and triplet states of the system P-4 are presented in detail.