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

Abstract

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 D 2 quantum crystal close to its melting.

High-pressure behavior of dense hydrogen up to 3.5 TPa from density functional theory calculations

“…[7][8][9][10] However, beyond the fact that protons remain paired within this pressure range, their time-average locations are to date experimentally unknown, mainly because hydrogen atoms scatter X-rays only weakly, leading to low-resolution diffraction patterns. 7,11 Experimental data at higher pressures are scarce, and insightful understanding of structural behavior of ultra-dense hydrogen is lacking.…”