Accuracy of buffered-force QM/MM simulations of silica.

摘要: We report comparisons between energy-based quantum mechanics/molecular mechanics (QM/MM) and buffered force-based QM/MM simulations in silica. Local quantities—such as density of states, charges, forces, geometries—calculated with both approaches are compared to the results full QM simulations. find length scale over which forces computed using a finite region converge reference values obtained quantum-mechanical calculations is ∼10 A rather than ∼5 previously reported for covalent materials such silicon. Electrostatic embedding surrounding classical point charges gives only minor contribution force convergence. While approach provides accurate geometry optimizations defects, we that removal large errors at boundary provided by scheme necessary constrained where Si–O bonds elongated finite-temperature molecular dynamics crack propagation. Moreover, allows more flexibility, since special-purpose coupling terms link MM atoms not required treated level can be adaptively redefined during course dynamical simulation.