Include single point energies calculations from LAMMPS or other MD code as unit tests

[emarinri]

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We could include single point energy calculations for simple systems such as bulk methane, ethanol, water, benzene from LAMMPS as unit tests in Cassandra. This would test the integration of several energy subroutines, such as those that compute intra- and intermolecular interactions, tail corrections, long-range electrostatics, etc.