Superconductivity and strong anharmonicity in novel Nb-S phases.

In this work we explore the phase diagram of the binary Nb-S system from ambient pressures up to 250 GPa usingevolutionary crystal structure prediction. We find several new stable compositions and phases, especially in the high-pressure regime, and investigate their electronic, vibrational, and superconducting properties. Our calculations show that all materials, besides the low-pressure phases of pure sulfur, are metals with low electron-phonon (ep) coupling strengths and critical superconducting temperatures below 15 K. Furthermore, we investigate the effects of phonon anharmonicity on lattice dynamics, ep interactions, and superconductivity for the novel high-pressure phase of NbS, demonstrating that the inclusion of anharmonicity stabilizes the lattice and enhances the ep interaction.