Comparing parallel and simulated tempering enhanced sampling algorithms at phase transition regimes

TL;DR

This paper compares parallel and simulated tempering algorithms for sampling phase transition regimes, finding that parallel tempering generally outperforms simulated tempering in convergence, tunneling frequency, and correlation decay.

Contribution

It provides a comparative analysis of PT and ST algorithms specifically at phase transition regimes, highlighting the advantages of PT over ST in such conditions.

Findings

Parallel tempering converges faster than simulated tempering.

PT exhibits higher tunneling frequency between phases.

Correlation functions decay more rapidly with PT.

Abstract

Two important enhanced sampling algorithms, simulated (ST) and parallel (PT) tempering, are commonly used when ergodic simulations may be hard to achieve, e.g, due to a phase space separated by large free-energy barriers. This is so for systems around first-order phase transitions, a case still not fully explored with such approaches in the literature. In this contribution we make a comparative study between the PT and ST for the Ising (a lattice-gas in the fluid language) and the BEG (a lattice-gas with vacancies) models at phase transition regimes. We show that although the two methods are equivalent in the limit of sufficiently long simulations, the PT is more advantageous than the ST with respect to all the analysis performed: convergence towards the stationarity; frequency of tunneling between phases at the coexistence; and decay of time-displaced correlation functions of thermodynamic quantities. Qualitative arguments for why one may expect better results from the PT than the ST near phase transitions conditions are also presented.