Ab initio molecular dynamics: Propagating the density matrix with Gaussianorbitals. II. Generalizations based on mass-weighting, idempotency, energyconservation and choice of initial conditions

A generalization is presented here for a newly developed approach to ab ini tio molecular dynamics, where the density matrix is propagated with Gaussia n orbitals. Including a tensorial fictitious mass facilitates the use of la rger time steps for the dynamics process. A rigorous analysis of energy con servation is presented and used to control the deviation of the fictitious dynamics trajectory from the corresponding Born-Oppenheimer dynamics trajec tory. These generalizations are tested for the case of the Cl-(H2O)(25) clu ster. It is found that, even with hydrogen atoms present in the system, no thermostats are necessary to control the exchange of energy between the nuc lear and the fictitious electronic degrees of freedom. (C) 2001 American In stitute of Physics.