Zone-Centre Lattice Vibrations in α-Sulphur Including Effects of Hydrostatic Pressure

Abstract

2. Calculation methods 2.1. Dynamical matrix Zone-centre lattice vibrations in a-sulphur including effects o f hydrostatic pressure. J .

Raman Studies of Sulfur Crystal (α-S8) at High Pressures and Low Temperatures

“…36 Kurittu has studied the effects of hydrostatic pressure changes on the unit cell by minimizing the crystal free energy, he calculated pressure shifts of the frequencies of external and internal modes by means of lattice dynamics in the pressure range 0-1 GPa. 37,38 The resulting mode Gru ¨neisen parameters were found to be in good agreement with the experimental values given by Zallen. 24 No data at high pressure and low temperatures can be found in the literature.…”

“…Theoretical pressure dependencies were obtained by Pawley and Mika using a lattice dynamical calculation based upon an atom−atom pair potential . Kurittu has studied the effects of hydrostatic pressure changes on the unit cell by minimizing the crystal free energy, he calculated pressure shifts of the frequencies of external and internal modes by means of lattice dynamics in the pressure range 0−1 GPa. , The resulting mode Grüneisen parameters were found to be in good agreement with the experimental values given by Zallen …”

Lattice Statics with Deformable Molecules: α-Sulphur Under Hydrostatic Pressure

“…A similar model has previously been applied [18] to a calculation of the molecular distortion in orthorhombic sulphur, but, as discussed below, the present calculation differs from the previous one in some important details, such as in the choice of parameters for describing the intermolecular and intramolecular forces. Furthermore, the calculation has now been extended to include the structure of the crystal under hydrostatic pressure and, in the following paper [19] , lattice dynamics.…”

Theoretical Study of the Thermochemistry of Sulfur Molecular Crystals. I. Method and Application to α- and 1D-Polymerized Sulfurs

“…42 In Rinaldi and Pawley's potential, (i) there is no C 8 or three-body terms and (ii) the numerical values of repulsive parameters are not extracted from an independent quantum mechanical calculation. With their adjusted "6-exp" potential all the cited authors [42][43][44] were able to find a correct agreement between their calculated lattice frequencies and the experimental ones. We have shown in our examples how the C 8 and three-body terms may be important quantities for determining the right cohesive energy.…”

“…They use the so-called “6-exp” potential function (the r -6 term as the attractive part and the exponential function for the repulsive one), but the parameters C 6 , A r , and b r (in our notations) are adjusted in order to have the right geometrical structure and sublimation energy. Then they use the ad hoc potential in a dynamic calculation to study intermolecular vibrational modes, − internal ones in a nonrigid body model, and Raman frequencies . As a first remark, let us stress on the parameters values.…”