  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.
