High-pressure liquid hydrogen across molecular dissociation.
II - Fisica della materia
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We studied the transformation from molecular-insulating to monatomic-metallic fluid hydrogen upon increasing pressure, by first-principle simulations based on both Density Functional Theory (DFT) and Quantum Monte Carlo (QMC) methods. Below a critical temperature (estimated between 1500 K and 3000 K), the transition is first order with a discontinuity in the specific volume, a sudden dissociation of the molecules and a discontinuous change in electronic properties like the momentum distribution and the electrical conductivity. Above the critical point the transformation into the metallic dissociated state is continuous. Optical response of the system is obtained within the Kubo-Greenwood framework of DFT. Agreement with recent experimental results at NIF for reflectivity and absorption is observed. Our analysis suggests a coherent picture for apparently discordant experiments from different methods.