Density-functional calculations of the electronic structure and lattice dynamics of superconducting LaO_(0.5)F_(0.5)BiS₂: Evidence for an electron-phonon interaction near the charge-density-wave instability

We discuss the electronic structure, lattice dynamics and electron-phonon interaction of newly discovered superconductor LaO$_{0.5}$F$_{0.5}$BiS$_{2}$ using density functional based calculations. A strong Fermi surface nesting at $\mathbf{k}$=($\pi $,$\pi $,0) suggests a proximity to charge density wave instability and leads to imaginary harmonic phonons at this $\mathbf{k}$ point associated with in-plane displacements of S atoms. Total energy analysis resolves only a shallow double-well potential well preventing the appearance of static long-range order. Both harmonic and anharmonic contributions to electron-phonon coupling are evaluated and give a total coupling constant $\lambda \simeq 0.85$ prompting this material to be a conventional superconductor contrary to structurally similar FeAs materials.