A molecular dynamics simulation of a water droplet by the implicit-Euler/Langevin scheme

Results are presented from potential energy minimization of water clusters and from molecular dynamics and Monte Carlo simulations of a liquid water droplet model. A new method for molecular dynamics - the implicit-Euler/Langevin scheme - is used in combination with a truncated Newton minimizer for potential energy functions. Structural and thermodynamic properties are reported for the scheme (with time steps of 5 and 10 fs), compared to a standard explicit formulation (with Δt = 1 fs), to a Monte Carlo simulation, and to available experimental data. Results demonstrate that the implicit scheme is computationally feasible for large-scale biomolecular simulations, and that the droplet model can reasonably reproduce general structural features of liquid water. Results also show that the desired behavior is obtained from the implicit formulation: stability over large time steps, and effective damping of the high-frequency vibrational modes. Thus, major "bulk" properties of the system of interest may be observed more rapidly.