Missing theoretical evidence for conventional room-temperature superconductivity in low-enthalpy structures of carbonaceous sulfur hydrides

To elucidate the geometric structure of the putative room-temperature superconductor, carbonaceous sulfur hydride (C-S-H), at high pressure, we present the results of an extensive computational structure search of bulk C-S-H at 250 GPa. Using the minima hopping structure prediction method coupled to the GPU-accelerated sirius library, more than 17 000 local minima with different stoichiometries in large simulation cells were investigated. Only 24 stoichiometries are favorable against elemental decomposition, and all of them are carbon-doped ${\mathrm{H}}_3\mathrm{S}$ crystals. The absence of van Hove singularities or similar peaks in the electronic density of states of more than 3000 candidate phases rules out conventional superconductivity in C-S-H at room temperature.

Figure 1

The ternary convex hull of formation enthalpy generated from 140 stoichiometries explored at 250 GPa. The formation enthalpy per atom can be read off the color bar. In addition we zoom into the three sections of interest that were studied in detail (central, high H, and doping) in Figs. 2, 3, and 4, respectively.

Figure 2

Center region of the ternary phase diagram at 250 GPa.

Figure 3

Hydrogen-rich region of the ternary phase diagram at 250 GPa.

Figure 4

Carbon doping region of the ternary phase diagram at 250 GPa. The DOS of the structures lying on a gray dashed line are displayed in one of the plots of Fig. 7.

Figure 5

Comparison of formation enthalpy difference per atom between a PBE and an LDA functional at 250 GPa.

Figure 6

A selection of the most promising structures with regards to their formation enthalpy and DOS at 250 GPa.

Figure 7

Density of states in the carbon doping region at 250 GPa. The plots are normalized by the number of atoms and shifted downwards with increasing carbon doping ratio.

Figure 8

The ternary convex hull of formation enthalpy at 300 GPa.