Eur. Phys. J. E (2017) 40: 98
https://doi.org/10.1140/epje/i2017-11588-2

Regular Article

“Swarm relaxation”: Equilibrating a large ensemble of computer simulations^⋆

¹ Department of Physics and Physical Oceanography, Memorial University of Newfoundland, A1B 3X7, St. John’s, Newfoundland, Canada
² Department of Chemistry, University of Saskatchewan, 57N 5C9, Saskatoon, SK, Canada
³ Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale A. Moro 5, 00185, Roma, Italy
⁴ Department of Physics, St. Francis Xavier University, B2G 2W5, Antigonish, NS, Canada

^* e-mail: ppoole@stfx.ca

Received: 15 September 2017
Accepted: 27 October 2017
Published online: 10 November 2017

Abstract

It is common practice in molecular dynamics and Monte Carlo computer simulations to run multiple, separately-initialized simulations in order to improve the sampling of independent microstates. Here we examine the utility of an extreme case of this strategy, in which we run a large ensemble of M independent simulations (a “swarm”), each of which is relaxed to equilibrium. We show that if M is of order , we can monitor the swarm’s relaxation to equilibrium, and confirm its attainment, within , where is the equilibrium relaxation time. As soon as a swarm of this size attains equilibrium, the ensemble of M final microstates from each run is sufficient for the evaluation of most equilibrium properties without further sampling. This approach dramatically reduces the wall-clock time required, compared to a single long simulation, by a factor of several hundred, at the cost of an increase in the total computational effort by a small factor. It is also well suited to modern computing systems having thousands of processors, and is a viable strategy for simulation studies that need to produce high-precision results in a minimum of wall-clock time. We present results obtained by applying this approach to several test cases.