Generalized ensemble method applied to study systems with strong first order transitions
Abstract
At strong firstorder phase transitions, the entropy versus energy or, at constant pressure, enthalpy, exhibits convex behavior, and the statistical temperature curve correspondingly exhibits an Sloop or backbending. In the canonical and isothermalisobaric ensembles, with temperature as the control variable, the probability density functions become bimodal with peaks localized outside of the Sloop region. Inside, states are unstable, and as a result simulation of equilibrium phase coexistence becomes impossible. To overcome this problem, a method was proposed by Kim, Keyes and Straub, where optimally designed generalized ensemble sampling was combined with replica exchange, and denoted generalized replica exchange method (gREM). This new technique uses parametrized effective sampling weights that lead to a unimodal energy distribution, transforming unstable states into stable ones. In the present study, the gREM, originally developed as a Monte Carlo algorithm, was implemented to work with molecular dynamics in an isobaric ensemble and coded into LAMMPS, a highly optimized open source molecular simulation package. Lastly, the method is illustrated in a study of the very strong solid/liquid transition in water.
 Authors:
 Boston Univ., Boston, MA (United States)
 Broad Institute of Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Harvard Univ., Cambridge, MA (United States)
 Publication Date:
 Research Org.:
 Boston Univ., MA (United States)
 Sponsoring Org.:
 USDOE
 Contributing Org.:
 Boston University Center for Computational Science
 OSTI Identifier:
 1247484
 Grant/Contract Number:
 SC0008810
 Resource Type:
 Journal Article: Accepted Manuscript
 Journal Name:
 Journal of Physics. Conference Series
 Additional Journal Information:
 Journal Volume: 640; Journal Issue: 2; Conference: XXVI IUPAP Conference on Computational Physics (CCP2014) , Boston, MA (United States), 1114 Aug 2014; Journal ID: ISSN 17426588
 Publisher:
 IOP Publishing
 Country of Publication:
 United States
 Language:
 English
 Subject:
 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; 97 MATHEMATICS AND COMPUTING; phase transitions; computer simulation; algorithm design; water; freezing; melting
Citation Formats
Malolepsza, E., Kim, J., and Keyes, T. Generalized ensemble method applied to study systems with strong first order transitions. United States: N. p., 2015.
Web. doi:10.1088/17426596/640/1/012003.
Malolepsza, E., Kim, J., & Keyes, T. Generalized ensemble method applied to study systems with strong first order transitions. United States. doi:10.1088/17426596/640/1/012003.
Malolepsza, E., Kim, J., and Keyes, T. Mon .
"Generalized ensemble method applied to study systems with strong first order transitions". United States.
doi:10.1088/17426596/640/1/012003. https://www.osti.gov/servlets/purl/1247484.
@article{osti_1247484,
title = {Generalized ensemble method applied to study systems with strong first order transitions},
author = {Malolepsza, E. and Kim, J. and Keyes, T.},
abstractNote = {At strong firstorder phase transitions, the entropy versus energy or, at constant pressure, enthalpy, exhibits convex behavior, and the statistical temperature curve correspondingly exhibits an Sloop or backbending. In the canonical and isothermalisobaric ensembles, with temperature as the control variable, the probability density functions become bimodal with peaks localized outside of the Sloop region. Inside, states are unstable, and as a result simulation of equilibrium phase coexistence becomes impossible. To overcome this problem, a method was proposed by Kim, Keyes and Straub, where optimally designed generalized ensemble sampling was combined with replica exchange, and denoted generalized replica exchange method (gREM). This new technique uses parametrized effective sampling weights that lead to a unimodal energy distribution, transforming unstable states into stable ones. In the present study, the gREM, originally developed as a Monte Carlo algorithm, was implemented to work with molecular dynamics in an isobaric ensemble and coded into LAMMPS, a highly optimized open source molecular simulation package. Lastly, the method is illustrated in a study of the very strong solid/liquid transition in water.},
doi = {10.1088/17426596/640/1/012003},
journal = {Journal of Physics. Conference Series},
number = 2,
volume = 640,
place = {United States},
year = {Mon Sep 28 00:00:00 EDT 2015},
month = {Mon Sep 28 00:00:00 EDT 2015}
}

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