The transfer Hamiltonian: a tool for large scale simulations with quantum mechanical forces

We report a method for the inclusion of accurate quantum mechanical forces in large scale molecular dynamics simulations by defining a transfer Hamiltonian containing only one and two-center terms that are modeled by parametric functions. The parameters of the transfer Hamiltonian are fit such that interatomic forces computed ab initio at the CCSD/DZP level of theory for the reactions C2H6→2CH3, Si2H6→2SiH3, and Si2O7H6→Si(OH)3+SiO(OH)3 are accurately modeled. Use of the transfer Hamiltonian, which is electronic state specific, requires several orders of magnitude less time and disk space than do the ab initio calculations, thus they are suitable for treating the quantum region of multi-scale simulations for systems containing ≈103 atoms.