Superconductivity in LaO: a density functional theory study with local, semilocal, and nonlocal exchange-correlation functionals

We studied the dynamical, electronic, and superconducting properties of LaO using a local (PZ), a semilocal (PBE), and three nonlocal correlation functionals (rVV10, vdW-DF2, and vdW-DF3) of the density-functional theory. We concluded that the nonlocal correlations have a marginal effect on the electronic band energies near the Fermi surface. However, the corresponding shifts in the density of states are relatively significant. In contrast, the phonon energies get modified by larger amounts, particularly for optical phonons. These variations in energies of optical phonons do not get reflected to the same degree in electron-phonon coupling constant, lambda, from different functionals as their contribution in lambda is minor that ranges from 21% to 33%. Moreover, the imperative role of Kohn anomalies and Fermi surface nesting for the electron-phonon coupling is reconfirmed. We also highlighted the role of the matrix elements that surpasses, in certain parts of the Brillouin Zone, all other factors including the Fermi surface nesting. The nonlocal correlation functional, vdW-DF2, gives significantly different results than other nonlocal as well as local/semilocal functionals due to excessive low energy phonons and larger phonon linewidth.