The transfer Hamiltonian: A tool for large scale, accurate, molecular dynamics simulations using quantum mechanical potentials

The accuracy of a molecular dynamics simulation is contingent upon the quality of the potentials used to compute the intermolecular forces on the constituent atoms. The most accurate potentials are those which result from first principles quantum mechanics computations such as coupled cluster theory; however, for large scale molecular dynamics which may be on the order of 1000's of atoms, this is computationally not feasible as most ab initio potentials are limited to 10's or 100's of atoms. In order to avoid this computational bottleneck, the concept of a transfer Hamiltonian is introduced. The transfer Hamiltonian is a low rank, quantum mechanical operator whose matrix elements are computed from parametric functional forms. The parameters which constitute the transfer Hamiltonian are fit to ab initio coupled cluster theory results (ionization potentials, geometry, dissociation energies, etc.) for several small model systems which mimic the local structure of the target simulation system. The transfer Hamiltonian is applicable to systems far beyond the reach of ab initio coupled cluster theory, yet it retains the accuracy of the first principles computation. Further, since the transfer Hamiltonian can be rapidly evaluated, it is useful for on-the-fly molecular dynamics simulations and gives results which are more accurate than those obtainable using a classical potential.