Superconductivity and topological properties of -type diborides from first principles

The superconductivities and topological properties of -type diborides are investigated by means of first-principles calculations with different exchange-correlation functionals. Functionals with the van der Waals (vdW) correction (such as OptB88-vdW) may predict critical temperature () comparable with experimental results for several -type superconductors, particularly for the pristine (39.3 vs 39 K). Interestingly, the spin-fluctuation is found to play a significant role in the superconducting behavior of diborides with transition metal elements, and their can be enhanced monotonically by applying tensile strains. Furthermore, Dirac surface states of and are revealed, suggesting their potential use as topological superconducting materials. This paper provides a useful guideline for ab initio studies of superconductivities and topological properties of vdW layered materials.