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   COLLOQUIUM OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS        
        Institute for Computational Sciences and Informatics	
                           (CSI 898-Sec 001) 
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    The elastic properties and the electronic structure of lead
	 chalcogenide semiconductors: PbTe, PbSe, PbS

			Mohammed Lach-hab

            Institute for Computational Sciences, GMU and
             Center for Computational Materials Science
            Naval Research Laboratory, Washington, D. C.

Full potential linearized augmented plane wave (FP LAPW) calculations were 
performed to study several properties of Lead Chalcogenide semiconductors 
(PbS, PbSe, PbTe) using the Local Density (LDA) and the Generalized Gradient 
(GGA) Approximation of the exchange-correlation energy. In this study we 
present calculations of the band structure, density of states and the total
energy as a function of volume in both the (NaCl) and (CsCl) structures.
The stability of these phases was also considered by calculating the elastic 
constants. The energy band gap, the bulk modulus, the equilibrium lattice 
constants, and the elastic constants are compared with experiment and other 
calculations. In the case of (PbTe) we have found that the local density 
approximation (LDA) results in an energy gap that overestimates the 
experimental value, in contrast to most materials where the the energy gap 
is underestimated. This is a shortcoming of the LDA which is magnified in 
our LAPW calculations by the omission of the spin-orbit interaction.
In addition we have performed a Slater-Koster fit using an orthogonal basis 
set of s and p orbitals and we have included the spin-orbit coupling in the 
Slater-Koster formalism of tight-binding theory. Using this method we have 
adjusted the gap to the experimental value.

                          Monday , April 10, 2000
                                  4:30 pm
                        Room 206, Science & Tech. I

Refreshments will be served.
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Find the schedule at http://csi.gmu.edu/lcdm/seminar/schedule.html