Neutron diffraction determination of the microscopic structure of solid deuterium close to melting

The static structure factor of solid normal deuterium, close to its triple point, has been measured using time-of-flight neutron diffraction. Experimental results have been compared to path-integral Monte Carlo simulations as well as to a simple uncorrelated lattice calculation including the mean-squared displacement as an adjustable parameter. We found a very good agreement between experimental data and quantum simulations in all the measured range, while the uncorrelated model, as expected, turned out to be satisfactory only at long distances and for a mean-squared displacement value almost twice as large as the low-temperature one. This fact can be ascribed to the large anharmonic character of the D₂ quantum crystal close to its melting.