Aspects of phonon spectra for classical Gaussian core models

Frank H. Stillinger
2005 Physical Review B  
Calculations have focused on several key aspects of phonon spectra for the stable lattice structures of the Gaussian core model. These structures include the linear array ͑D =1͒, the close-packed triangular lattice ͑D =2͒, and the low-density face-centered and high-density body-centered-cubic lattices ͑D =3͒. In each dimension, compressing the system isotropically eventually causes strong depression of phonon frequencies for wave vectors approaching the Brillouin zone boundary, and this
more » ... y, and this depression moves inward toward the k-space origin with increasing compression. Phonon spectra for uniformly shear-strained triangular lattices illustrate the development of mechanical instability for those systems, also with increasing compression. For D = 3, the unstrained face-centered-cubic lattice exhibits an upper density limit of mechanical stability owing to development of a "soft" long-wavelength transverse mode and the unstrained body-centered-cubic lattice displays an analogous lower density limit due to a corresponding "soft" long-wavelength transverse mode; furthermore, those upper and lower limiting densities satisfy the basic Gaussian core model duality relation. Finally, these various phonon characteristics are tied to the negative thermal expansions possessed by the model and to the density-dependent potential energy landscape as it relates to the melting transition.
doi:10.1103/physrevb.71.024301 fatcat:d7eiwaukafhsfhsqweja36hfem