Lattice dynamics for isochorically heated metals: A model study

The electron-excitation induced bond strength variations in metals have been predicted from density-functional theory calculations and observed experimentally, while the microscopic mechanism has yet to be elucidated. Here, we present a minimal model that reproduces the phonon hardening and softening for fcc- and bcc-structured metals as a result of the electron thermal excitation. For the cases of bcc-structured metals, a delicate balance between the first and second nearest neighbor force constants leads to a phonon softening at the N point.