Free energies of crystals computed using Einstein crystal with fixed center of mass and differing spring constants

Vikram Khanna, Jamshed Anwar, Daan Frenkel, Michael F. Doherty, Baron Peters

Research output: Contribution to journalArticlepeer-review

Abstract

Free energies of crystals computed using a center of mass constraint require a finite-size correction, as shown in previous work by Polson et al. [J. Chem. Phys. 112, 5339-5342 (2000)]. Their reference system is an Einstein crystal with equal spring constants. In this paper, we extend the work of Polson et al. [J. Chem. Phys. 112, 5339-5342 (2000)] to the case of differing spring constants. The generalization is convenient for constraining the center of mass in crystals with atoms of differing masses, and it helps to optimize the free energy calculations. To test the theory, we compare the free energies of LiI and NaCl crystals from calculations with differing spring constants to those computed using equal spring constants. Using these center of mass finite size corrections, we compute the true free energies of these crystals for different system sizes to eliminate the intrinsic finite-size effects. These calculations help demonstrate the size of these finite-size corrections relative to other contributions to the absolute free energy of the crystals.

Original languageEnglish (US)
Article number164509
JournalJournal of Chemical Physics
Volume154
Issue number16
DOIs
StatePublished - Apr 28 2021

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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