Thermodynamic properties of a quantum chain with nearest-neighbor anharmonic interactions

The path integral for the quantum partition function of a chain of atoms with nearest-neighbor interaction is calculated by a variational method. This approach turns out to be very rapid and powerful; it is able to describe the quantum properties of the system in the ''solid'' phase. Application with the Lennard-Jones potential is made and explicit results for internal energy and specific heat are shown. Our technique based on the effective potential offers an alternative to the quantum Monte Carlo approach.