Phonon Self-Energies in Weakly and Strongly Anharmonic Systems.
Abstract
The interatomic forces in a crystal are usually strongly dependent on the interatomic spacing and consequently the lattice potential energy for a crystal can generally be written as a power series in the displacements of the atoms from their equilibrium positions. If such an expansion is terminated at the quadratic terms, then this constitutes the so-called harmonic approximation. In the harmonic approximation the lattice vibrations are true normal modes such that if energy is channeled uniquely into any one lattice mode, then it will remain undissipated in that mode. The harmonic approximation would therefore predict, for instance, that the scattering cross section for neutrons by a Bravais lattice would consist of a set of 8 function peaks or, analogously, that the spectral profiles of lattice vibrations would be a set of undamped temperature independent resonances. These and other such predictions are, of course, in marked discord with experimental results. It is therefore clear that the anharmonic terms in a lattice potential must be considered if a full understanding of many of the physical properties of solids is to be achieved. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 11, 1980
- Accession Number
- ADA095151
Entities
People
- Robert P. Lowndes
Organizations
- Northeastern University