Convective Replica-Exchange in Ergodic Regimes

TL;DR

This study evaluates convective-RE's performance in ergodic regimes, finding it beneficial mainly when bottlenecks or low acceptance probabilities hinder standard replica-exchange efficiency.

Contribution

It provides a detailed analysis of convective-RE's effectiveness in ergodic regimes, clarifying its advantages and limitations compared to standard schemes.

Findings

Convective-RE's maximum round-trip ratio is ~1.5 in ergodic regimes.

Standard-RE outperforms convective-RE at high acceptance probabilities.

Decoupling dynamics improves convective-RE efficiency at low acceptance probabilities.

Abstract

In a recent article (J. Comput. Chem. 2013, 34, 132-140), convective Replica-Exchange (convective-RE) has been presented as an alternative to the standard even-odd transition scheme. Computations on systems of various complexity have shown that convective-RE may increase the number of replica round-trips in temperature space with respect to the standard exchange scheme, leading to a more effective sampling of energy basins. Moreover, it has been shown that the method may prevent the formation of bottlenecks in the diffusive walk of replicas through the space of temperature states. By using an ideal temperature-RE model and a classical harmonic-oscillator RE scheme, we study the performances of convective-RE when ergodicity is not broken and convergence of acceptance probabilities is attained. In this dynamic regime, the round-trip ratio between convective and standard-RE is at maximum ~1.5, a value much smaller than that observed in non-ergodic simulations. For large acceptance probabilities, the standard-RE outperforms convective-RE. Our observations suggest that convective-RE can safely be used in either ergodic or non ergodic regimes; however, convective-RE is advantageous only when bottlenecks occur in the state-space diffusion of replicas, or when acceptance probabilities are globally low. We also show that decoupling of the state-space dynamics of the stick replica from the dynamics of the remaining replicas improves the efficiency of convective-RE at low acceptance probability regimes.