Path-integral Monte Carlo simulation of the structure of deuterium in the critical region

The site-site distribution function and structure factor of deuterium close to the critical point have been calculated by means of quantum path-integral Monte Carlo simulations. The calculations were performed using a spherically symmetric pairwise-additive potential for the distribution of the molecular center of mass and assuming that D₂ may be regarded as a classical free rotor. Some of the problems connected with the simulation of a quantum system close to the critical point are analyzed in detail. The results of the simulations have been compared with the neutron-scattering experiment by Zoppi et al. [Phys. Rev. A 39, 4684 (1989)]. The overall agreement is excellent, but some diffuse discrepancies are found. Possible origins of this inconsistency are discussed.