Quantum Monte Carlo calculation of the thermodynamic functions of a Lennard-Jones chain of atoms

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Abstract
The internal energy, pressure, and specific heat of an anharmonic chain of atoms are calculated using path-integral quantum Monte Carlo techniques. The atoms in the chain are taken to be point masses which interact with their neighbors through a Lennard-Jones potential. Chains of such atoms with nearest-neighbor-only interactions and with nearest-neighbor and second-nearest-neighbor interactions are considered. Up to 160 000 000 configurations are sampled for each data point of energy, pressure, or specific heat presented. Comparison with the classical limit solution of this system is made to determine the region in which quantum effects become important. Comparison with the harmonic approximation to the quantum solution is used to determine when anharmonic effects become important.