Using the density-functional perturbation theory with structural optimization, we investigate the electronic structure, phonon spectra, and superconductivity of BiS 2 -based layered compounds LaO 1−x F x BiS 2 . For LaO 0.5 F 0.5 BiS 2 , the calculated electron-phonon coupling constant is equal to λ = 0.8, and obtained T c ≃ 9.1 K is very close to its experimental value, indicating that it is a conventional electron-phonon superconductor.

The electronic structure, phonon dispersions, and electron-phonon (EP) coupling in Fe2Se2/SrTiO3 (FeSe/STO) thinnest films are studied based on the first-principles calculations. It is found that the FeSe/STO interface with lattice strain leads to a change of band structures and a significant enhancement of the EP coupling, the latter being close related to interface-induced ferroelectric phonons coupled to electrons on the FeSe monolayer. In the FeSe/STO system, Tc of phonon-induced superconductivity is estimated to be much greater than that in the bulk FeSe, but still well below the experimental value of an FeSe monolayer on the STO substrate, indicating that the electron-phonon mechanism alone cannot explain its high Tc.

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