Ab initio and semiempirical methods for molecular dynamics simulations based on general Hartree--Fock theory

We present two new methods for molecular dynamics simulations based on general HartreeFock (GHF) theory. The first method involves approximating ab initio STO-3G matrix elements with fitting functions to enable faster computation of the energy and forces for molecular dynamics simulations. The implementation of this method includes a frozen-core approximation. The second method involves developing semiempirical potentials by reparametrizing the fitting functions obtained in the first method to fit experimental data. This second method enables us to reproduce experimental quantities with only the computational effort of an STO-3G calculation. We successfully applied both of these methods in conjunction with the Car-Parrinello ab initio molecular dynamics method to the geometry optimization of lithium clusters, cationic and neutral, of up to five atoms.