رسائل ماجيستير
English
2005
Self-Consistent Field Calculations for the Effect of Pressure and Temperature on Some Properties of Grey Tin Crystal
Ahmed M. Abdul-Lettif , Mudar A. Abdul - Sattar, محمد غانم مردان
كلية العلوم-جامعة بابل · العراق
A large unit cell (LUC) formalism of eight atoms within intermediate neglect of differential overlap (INDO) is used to study some properties of grey tin crystal and to investigate the effect of pressure and temperature on these properties. Correlation corrections are added to this model and taking the spin-orbit splitting into consideration. Cohesive energy, direct band gap, valance band width, conduction band width and hybridized orbitals of the crystal are obtained from the band structure calculations. Bulk modulus, valance charge distribution and x-ray scattering factors are also calculated. All the aforementioned properties are obtained by selecting empirical parameter sets for (LUC-INDO) model. It is found that the equilibrium lattice constant, cohesive energy, x-ray scattering factors are in good agreement with the experimental results. The direct band gap and bulk modulus are greater than the experimental values. The effect of compressive stress on the aforementioned properties is investigated . It is found that the direct band gap, valance band width and p state occupation increase with increasing the compressive stress, whereas the conduction band width and form factors decrease. The reverse of these behaviours are found with the effect of tensile stress. The maximum value of stress is taken to be 1GPa,because at this value Sn transforms to Sn. The effect of temperature on these properties is studied below 1.31oC because beyond this value Sn has phase transition to Sn. The effect of temperature in the present work represents the change of the properties due to the change in the lattice constant of the crystal. It is found that the conduction band width, s state occupation and form factors increase with increasing the temperature, while the direct band gap and valance band width decrease. It is concluded that the (LUC-INDO) method gives good results when choosing optimum empirical parameter sets and it has a reliable prediction for the effect of pressure. This model is deficient for the effect of temperature because the adding of the vibrational contribution to free energy of the crystal is necessary. Abstract