New approach to the calculation of ground-state properties in solids

Abstract

A novel application of the minimum property of the ground-state energy, within the density-functional approach, enables us to obtain a simple and accurate expression for total energy differences. The crucial role here is played by the difference between one-electron energies, under a "frozen"-potential condition. This way we can explain the energy cancellations responsible for the success of the $d$-bond model in transition metals and their compounds. In an expression obtained for shear and phonons, two important energy terms are present. One is essentially ionic and describes a renormalized "bare" phonon. The other is essentially covalent and expressed again by differences between one-electron energies under the frozen-potential condition. This expression justifies the use of approximations based on a rigidly displaced potential for electron-phonon coupling calculations, which yielded good results for transition metals in the past. Their success is shown to be based on the fact that the frozen-potential condition accounts well for the many-body effects associated with the electron-phonon coupling process, because under this condition self-consistency and screening effects are mutually canceled.