Ricerc@Sapienza

Almost 80 years ago it was predicted that hydrogen, under sufficient compression, would break its molecular bonds and form a new metallic solid state.
This new state is predicted to be a room temperature superconductor [Ashcroft 1968].
Its experimental realization is actually one of the main goals of solid state physics. The task has proven to be more challenging than expected, due to a very rich phase diagram that high-pressure hydrogen exhibits.

At this high pressure, it is impossible to obtain the crystal structure from diffraction data. Optical data, vibrational IR and Raman spectroscopy can be used to determine phase transitions but requires a theoretical analysis to determine the crystal structures. The goal of this project is the first-principles prediction of the (T, P) phase diagram of H and the simulation of the IR and Raman spectra of the stables phases. In both tasks, we will take into account the anharmonic thermal and quantum fluctuations of H atoms, thanks to a new numerical method introduced by our group members during this year.

These effects play a crucial role in phase stability and in superconductive proprieties, as recently proved by many calculations [Errea et.al. 2016, Borinaga et. al. 2016A, Borinaga et. al. 2016B].

The predicted IR-Raman phonon dispersion will be compared to the experimental signatures of H phase diagram to shed light on recent claims about the effective observation of the solid state of hydrogen.

[Ashcroft - Physical Review Letters - 1968]
[Borinaga, Errea, Calandra, Mauri, Bergara - Physical Review B - 2016A]
[Borinaga, Riego, Leonardo, Calandra, Mauri, Bergara, Errea - Journal of Physics: Condensed Matter - 2016B]
[Errea, Calandra, Pickard, Nelson, Needs, Li, Liu, Zhang, Ma, Mauri - Nature - 2016]