Electronic structures, lattice dynamics, and electron–phonon coupling of simple cubic Ca under pressure

The electronic band structures, lattice dynamics and electron–phonon coupling (EPC) of simple cubic (sc) Ca under pressure have been investigated using first-principles calculations. Analysis of the calculated band structure and Fermi surface with pressure suggests that the predicted electronic topology transitions (ETT) at the XX point is mainly responsible for the observed anomaly of the electrical resistance. The phonon calculations for sc Ca with both supercell and linear response methods reveal large imaginary frequencies in the pressure range of 32–109 GPa. This phonon instability might imply the existence of significant anharmonic effect in sc Ca needed to stabilize the crystal. In addition, EPC calculation demonstrates that the observed increase of the superconducting transition temperature TcTc with pressure is mainly attributed to the enhancement of the electron density of state at the Fermi level N(EF)N(EF) and the EPC matrix element 〈I2〉〈I2〉.