Enhanced Coulomb pseudopotentials in high-pressure hydrides from first principles

In the Eliashberg theory of superconductivity, Coulomb interactions oppose the phonon-mediated attraction and suppress the superconducting critical temperature T c. However, most first-principles predictions continue to treat this repulsion with an empirical Coulomb pseudopotential μ* ME in the range 0.1-0.15. Here we present first-principles calculations of the Coulomb parameter μ and pseudopotential μ* ME in superconducting hydrides across a range of pressures. The screened Coulomb interaction is evaluated at the random phase approximation level with the Mantel code. We demonstrate that several hydride systems, including H 3 S, YSbH 6 and Mg 2 IrH 6, have strong Coulomb repulsions driven by a large density of states at the Fermi energy, N F. For Mg 2 IrH 6 we obtain μ=0.62 and μ* ME about0.39, leading to a 40 K suppression in T c relative to a standard μ* ME=0.16. Our obtained μ* ME is far above the conventional range and, accounting for the energy dependence of the density of states, resolves the factor-of-two discrepancy between T c estimates of previous studies. Across all systems and pressures studied, we find that μ closely tracks N F, suggesting that commonly used μ* ME values lead to overestimated T c in materials where the density of states at the Fermi energy is large.