Chemical potential calculations in dense liquids using metadynamics

Abstract

The calculation of chemical potential has traditionally been a challenge in atomistic simulations. One of the most used approaches is Widom's insertion method in which the chemical potential is calculated by periodically attempting to insert an extra particle in the system. In dense systems this method fails since the insertion probability is very low. In this paper we show that in a homogeneous fluid the insertion probability can be increased using metadynamics. We test our method on a supercooled high density binary Lennard-Jones fluid. We find that we can obtain efficiently converged results even when Widom's method fails.

Chemical potentials of water, methanol, carbon dioxide and hydrogen sulphide at low temperatures using continuous fractional component Gibbs ensemble Monte Carlo

“…Hence, studying VLE of pure components or mixtures of different components requires knowledge of free energies to satisfy the condition of chemical equilibrium [6,8,11,12]. Likewise, knowledge of the chemical potential plays an important role in understanding processes such as chemical reactions, diffusion, phase transitions, mass transfer and the direction in which these processes take place [13][14][15]. However, the calculation of free energies has turned out to be much more difficult [16,17] compared to other properties such as density or pressure.…”

“…It is well known that WTPI method breaks down at high densities because of frequent overlaps between the test molecule and the molecules within the system [25][26][27]. Since spontaneous cavities large enough to fit a test molecule are less likely to occur in high-density phases, it renders the WTPI method inefficient or essentially useless [3,13,24,28] for computing chemical potentials.…”

Chemical potential calculations in non-homogeneous liquids

“…Let us now briefly recall the method we have proposed for homogeneous systems, presented in Ref. 29. First we make use of the fact that, in homogeneous fluids, exp [−β∆U (R * ; R)] N does not depend on R * , so that:…”

“…Here, stimulated by the interest in nano-fluidics and confined systems we lift this limitation and extend the ideas of Ref. 29 to non-uniform systems.…”

Editorial

“…Borrero and Dellago show how to use metadynamics in order to improve trajectory sampling when studying the transition path of a reaction [15]. Perego et al take a fresh look at the problem of calculating the chemical potential in dense liquids, using metadynamics [16].…”