Gruneisen relationship

DFT calculations of the static lattice were performed within the local density approximation (LDA) using planewave basis sets and ultrasoft pseudopotentials, and the results were used to construct a force constant matrix within a large superceU model. The phonon spectrum was then evaluated as a function of temperature using quasi-harmonic models that allowed us to constmct mode Gruneisen relationships [66] (Fig. 4.4). The results indicated a dip in the V(T) relation at 80 K, that was slightly smaller than that observed for diamond-structured Si (Fig. 4.5). 

In order to characterize the state of a material following constant volume heating, the pressure-energy coupling relationship must be known. The relationship is determined through the Gruneisen coefficient, T, of the material, as it appears in the Mie-Gruneisen equation of state [51], and can be written in... 

The Gruneisen parameter characterizing intermolecular bonds anhar-monicity level in polymer, is determined according to the following relationship [19] ... 

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