Pressure-induced high-temperature superconductivity in hypothetical H3X (X=As, Se, Br, Sb, Te and I) in the H3S structure with Im3¯m symmetry

The discovery of high critical temperature Tc superconductivity in highly compressed H3S has opened up the question of searching for strong electron–phonon coupling in the hydrides outside the transition metal series. The specific objective of this work is to explore the possibility of discovering a material that exceeds the superconducting transition temperature of H3S. Our study includes the materials H3X (X=As, Se, Br, Sb, Te, and I), is limited to the Im3¯m crystal structure. The procedure we adopt involves performing linearized augmented plane wave (LAPW) calculations for many different volumes to compute the electronic densities of states and their pressure variation. This is combined with Quantum-ESPRESSO (QE) calculations from which we obtain the phonon frequencies and the electron–phonon coupling constant λ, and followed by applying the multiple scattering-based theory of Gaspari and Gyorffy (GG) to obtain the Hopfield parameters and the McMillan–Allen–Dynes theory. It should be stressed that the GG approach decouples the electronic contribution to λ from the corresponding phonon contribution, and provides additional insights for the understanding of superconductivity in these materials. Based on our analysis, the hydrogen is the main contributor to the Tc in these materials as it makes up 75∼80 % of the total λ. Our calculations for H3Se and H3Br give a Tc ∼100 K. For the other materials in our study we find that H3As is unstable and H3Sb, H3Te and H3I have small values of the McMillan–Hopfield parameters which makes it unlikely to give high Tc. However, according to both of our rigid band model and virtual crystal calculations, we predict a Tc∼150 K for H3Br with a small amount of hydrogen doping. Our basic conclusion is that the materials studied here could not reach very high Tc because the Hopfield parameters, which are the strongest contributor to high Tc, are not large enough.