Electron-phonon coupling and exchange-correlation effects in superconducting H3S under high pressure

Abstract

We investigate the H3S phase of sulfur hydride under high pressure ≃200 GPa by means of ab initio calculations within the framework of the density-functional theory with the PBE0 hybrid exchange-correlation (Exc) approximation. The choice of Exc has the largest effect on the calculated electron-phonon coupling (EPC) matrix elements; the high-pressure equation of state and phonon frequencies are only slightly modified. Mode-dependent EPC correction factors are determined from PBE0 using a frozen-phonon supercell approach, while standard density-functional perturbation theory is used to determine the EPC with PBE generalized-gradient approximation Exc. Our principle finding is that the calculated PBE0 Tc is enhanced by 25% compared to PBE. This is similar in magnitude, but in opposite direction, to the proposed suppression of Tc by anharmonic effects [I. Errea et al., Phys. Rev. Lett. 114, 157004 (2015)]. Our calculations demonstrate the importance of considering exchange-correlation approximations for calculations of superconducting properties for this class of materials.

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