Calculation of the phonon frequencies of gamma -Fe in an anharmonic model

The equilibrium lattice constant and the bulk modulus of fcc iron are calculated by the FP-LMTO method. The use of the generalized gradient approximation in calculating the electron structure and lattice properties of gamma -Fe is discussed. A local minimum is observed on the curve of total energy versus the amplitude of the atomic displacements corresponding to transverse vibrations at the tungsten point of the Brillouin zone. The temperature dependence of the anharmonic mode effective frequency calculated within the framework of the pseudoharmonic approximation is found to qualitatively agree with the experimental one. The possibility of interpreting the structural phase transition as a transition of the 'active' phonon mode from the excited to the basic state is discussed.