Data di Pubblicazione:
2016
Citazione:
Infrared optical properties of α quartz by molecular dynamics simulations / F. Gangemi, R. Gangemi, A. Carati, A. Maiocchi, L. Galgani. - In: EUROPHYSICS LETTERS. - ISSN 0295-5075. - 116:3(2016 Nov). [10.1209/0295-5075/116/37001]
Abstract:
This paper is concerned with theoretical estimates of the refractive–index curves for
quartz, obtained by the Kubo formulæ in the classical approximation, through MD simulations
for the motions of the ions. Two objectives are considered. The first one is to understand the role
of nonlinearities in situations where they are very large, as at the α–β structural phase transition.
We show that on the one hand they don’t play an essential role in connection with the form of the
spectra in the infrared. On the other hand they play an essential role in introducing a chaoticity
which involves a definite normal mode. This might explain why that mode is Raman active in
the α phase, but not in the β phase. The second objective concerns whether it is possible in a
microscopic model to obtain normal mode frequencies, or peak frequencies in the optical spectra,
that are in good agreement with the experimental data for quartz. Notwithstanding a lot of effort,
we were unable to find results agreeing better than about 6%, as apparently also occurs in the
whole available literature. We interpret this fact as indicating that some essential qualitative
feature is lacking in all models which consider, as the present one, only short–range repulsive
potentials and unretarded long–range electric forces.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
optical constants; quartz; anharmonic lattice modes
Elenco autori:
F. Gangemi, R. Gangemi, A. Carati, A. Maiocchi, L. Galgani
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