Melting of quantum solids: Comparison of observable and path centroid properties

Quantum effects on melting are illustrated using path integral simulations of a Lennard-Jones model for bulk ortho-D-2 and para-H-2. The melting tempe rature is significantly lowered due to quantum effects. Thermodynamic prope rties and order parameters show a discontinuous change on melting. Observab le configurational properties of the system are compared with the correspon ding path centroid properties with a view to understanding the role played by quantum fluctuations. The difference between centroid and observable str uctural properties is shown to depend on both the nature of the observable and the radius of gyration.