Fock matrix dynamics

An efficient method is suggested for direct ab initio Born–Oppenheimer molecular dynamics. It is based on extrapolating the Fock matrices from previous time steps to provide a start for the SCF procedure. Several polynomial extrapolation schemes are compared; low-degree schemes work best. SCF convergence can be achieved in 2–3, sometimes less than two cycles. We have identified a phenomenon, hysteresis, a violation of the energy conservation and reversibility, due to systematic errors arising from incomplete SCF convergence. It can be eliminated by rescaling the velocities. Examples include water clusters and hydrated halogen ions, running simulations for several picoseconds.