High-Precision Shock Wave Measurements of Deuterium: Evaluation of Exchange-Correlation Functionals at the Molecular-to-Atomic Transition.

We present shock compression data for deuterium through the molecular-to-atomic transition along the principal Hugoniot with unprecedented precision, enabling discrimination between subtle differences in first-principle theoretical predictions. These observations, supported through reshock measurements, provide tight constraints in a regime directly relevant to planetary interiors. Our findings are in best agreement with density functional theory; however, no one exchange-correlation functional describes well both the onset of dissociation and the maximum compression along the Hugoniot.