abstract:The Grüneisen parameter, γ, named after Eduard Grüneisen, describes the effect that changing the volume of a crystal lattice has on its vibrational properties, and, as a consequence, the effect that changing temperature has on the size or dynamics of the lattice. The term is usually reserved to describe the single thermodynamic property γ, which is a weighted average of the many separate parameters γi entering the original Grüneisen's formulation in terms of the phonon nonlinearities.
Second, forlayercrystals the Grüneisen parameteralong theplane may be negativeforsometemperaturesbecauseofvibrationfilmeffects, butfor other crystals is positivealways.