High-pressure hydrogen sulfide by diffusion quantum Monte Carlo

Abstract

We revisit the enthalpy-pressure phase diagram of the various products from the different proposed decompositions of H 2 S at pressures above 150 GPa by means of accurate diffusion Monte Carlo simulations. Our results entail a revision of the ground-state enthalpy-pressure phase diagram. Specifically, we find that the C2/c HS 2 structure is persistent up to 440 GPa before undergoing a phase transition into the C2/m phase. Contrary to density functional theory, our calculations suggest that the C2/m phase of HS is more stable than the I4 1 /amd HS structure over the whole pressure range from 150 to 400 GPa. More importantly, we predict that the Im-3m phase is the most likely candidate for H 3 S, which is consistent with recent experimental x-ray diffraction measurements. Published by AIP Publishing. [http://dx

Favored decomposition paths of hydrogen sulfide at high pressure

“…Our finding that H 3 S 5 is a by-product in H 2 S decomposition is consistent with Goncharov's experimental results [14], and we further specify the pressure range of H 3 S 5 . The formation of sulfur and H 3 S at high pressure has been confirmed by plenty of theoretical and experimental reports [8,10,12,16,17], and HS 2 is considered as a product co-existed with H 3 S in experiments at pressure above 200 GPa [11], which are all in good agreement with our calculations. MBD interactions do not change decomposition paths of H 2 S solids, but can decrease the transition pressure of decomposition paths by 5-10 GPa (see figure 3(b)).…”

“…Therefore, understanding the origin of H 3 S is crucial in sufficiently utilizing its superconductivity. Many researches from both experimental and theoretical sides have confirmed that H 3 S is one of the decomposition products of H 2 S solids (or mixing with H 2 ) at high pressure [5,8,[10][11][12][13][14][15][16][17]. However, it is complex and controversial that how solid H 2 S is transformed into H 3 S, including the full reaction path, the intermediates and exact transition pressure of H 2 S decomposition.…”

“…As a typical molecular crystal, solid H 2 S at high pressure has attracted great interests regarding its decomposition [10][11][12][13][14][15][16][17][18] and metallization [19][20][21][22][23][24][25][26][27]. Initially, solid H 2 S was believed to dissociate into sulfur and hydrogen at 46 GPa due to the disappearance of the S-H stretching vibrations by infrared spectra, and experienced metallization at 96 GPa [19].…”

Nuclear quantum effects induce metallization of dense solid molecular hydrogen

“…In general, DMC calculations of excitations in crystals remain challenging because of the effect: The fractional change in the total energy due to the presence of a one‐ or two‐particle excitation is inversely proportional to the number of electrons in the simulation cell. As large simulation cells are required to provide an accurate description of the infinite solid, high‐precision calculations are necessary …”

“…As large simulation cells are required to provide an accurate description of the infinite solid, high-precision calculations are necessary. [36] Structures of crystalline materials are normally determined by X-ray or neutron diffraction methods. These techniques are very challenging for elements with low atomic numbers such as hydrogen, which is part of the reason the structures of phases III and IV have remained uncertain.…”