Note: Free energy calculations for atomic solids through the Einstein crystal/molecule methodology using GROMACS and LAMMPS

In this work the free energy of solid phases is computed for the Lennard-Jones potential and for a model of NaCl. The free energy is evaluated through the Einstein crystal/molecule methodologies using the molecular dynamics programs: GROMACS and LAMMPS. The obtained results are compared with the results obtained from Monte Carlo. Good agreement between the different programs and methodologies was found. The procedure to perform the free energy calculations for the solid phase in the molecular dynamic programs is described. Since these programs allow to study any continuous intermolecular potential (when given in a tabulated form) this work shows that for isotropic potentials (describing for instance atomic solids or colloidal particles) free energy calculations can be performed on a routinely basis using GROMACS and/or LAMMPS.