Nucleation rates from small scale atomistic simulations and transition state theory

TL;DR

This paper presents a general method to accurately compute nucleation rates from small atomistic simulations using transition state theory and enhanced sampling, avoiding classical approximations and finite size effects.

Contribution

It introduces a novel approach combining free energy barriers, TST, and metadynamics to determine nucleation rates from small systems without classical theory assumptions.

Findings

Accurate nucleation rates for argon vapor spanning sixteen orders of magnitude.

Method effectively overcomes finite size effects and slow time scales.

Results agree well with existing literature data.

Abstract

The evaluation of nucleation rates from molecular dynamics trajectories is hampered by the slow nucleation time scale and impact of finite size effects. Here, we show that accurate nucleation rates can be obtained in a very general fashion relying only on the free energy barrier, transition state theory (TST), and a simple dynamical correction for diffusive recrossing. In this setup, the time scale problem is overcome by using enhanced sampling methods, in casu metadynamics, whereas the impact of finite size effects can be naturally circumvented by reconstructing the free energy surface from an appropriate ensemble. Approximations from classical nucleation theory are avoided. We demonstrate the accuracy of the approach by calculating macroscopic rates of droplet nucleation from argon vapor, spanning sixteen orders of magnitude and in excellent agreement with literature results, all from simulations of very small (512 atom) systems.