Ab initio molecular dynamics with correlated molecular wave functions: Generalized valence bond molecular dynamics and simulated annealing

We present an ab initio molecular dynamics algorithm at the generalized valence bond level. It does not need a precalculated potential energy surface or model Hamiltonian; instead the nuclei move according to first principles forces derived from the electronic wave function which in turn follows the movement of the nuclei. This technique includes the dominant static electron correlations, it can treat ground and excited many-electron states, and it can describe chemical bond formation and breaking qualitatively correctly. We apply the method to Na₄, as a generic test example for small metal clusters, and show spin-dependent free dissociation dynamics as well as geometry optimization by simulated annealing. The latter involves novel boundary conditions to prevent dissociation and mass scaling to enhance performance.