Replica-Permutation Method with the Suwa-Todo Algorithm beyond the Replica-Exchange Method

TL;DR

The paper introduces the replica-permutation method (RPM) utilizing the Suwa-Todo algorithm, which enhances sampling efficiency in molecular simulations beyond the traditional replica-exchange method (REM).

Contribution

The novel RPM method allows permutations among multiple replicas and employs the Suwa-Todo algorithm to reduce rejection rates, improving sampling efficiency in molecular dynamics and Monte Carlo simulations.

Findings

RPM samples temperature and conformational space more efficiently than REM.

Successfully identified known structural features of C-peptide, including salt-bridges and alpha-helix formation.

Revealed detailed folding pathways with a two-step process.

Abstract

We propose a new method for molecular dynamics and Monte Carlo simulations, which is referred to as the replica-permutation method (RPM), to realize more efficient sampling than the replica-exchange method (REM).In RPM not only exchanges between two replicas but also permutations among more than two replicas are performed. Furthermore, instead of the Metropolis algorithm, the Suwa-Todo algorithm is employed for replica-permutation trials to minimize its rejection ratio. We applied RPM to particles in a double-well potential energy, Met-enkephalin in vacuum, and a C-peptide analog of ribonuclease A in explicit water. For a comparison purposes, replica-exchange molecular dynamics simulations were also performed. As a result, RPM sampled not only the temperature space but also the conformational space more efficiently than REM for all systems. From our simulations of C-peptide, we obtained the \alpha-helix structure with salt-bridges between Gly2 and Arg10 which is known in experiments. Calculating its free-energy landscape, the folding pathway was revealed from an extended structure to the \alpha-helix structure with the salt-bridges. We found that the folding pathway consists of the two steps: The first step is the "salt-bridge formation step", and the second step is the "\alpha-helix formation step".