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                SEMINAR OF THE DYNAMICAL SYSTEMS GROUP
        Institute for Computational Sciences and Informatics
				CSI 929
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	Electronic structure computations: modern techniques beyond mean-field
       theory.
			    Gerhard E. Engel
	   Institute for Computational Sciences and Informatics 
			George Mason University 
				  and
             		Complex Systems Theory Branch 
			  Naval Research Laboratory

Knowledge of the electronic excitation levels in a solid is crucial for
understanding many of its macroscopic and microscopic physical properties. 
In the past decades, enormous progress has been made in the development of 
so-called ab-initio techniques, allowing the prediction and simulation of 
material properties essentially without experimental input. The theoretical 
foundation for most of these calculations is provided by Density Functional 
Theory, which is essentially a mean-field treatment for the many-body problem.

Whereas Density Functional Theory is extremely well suited for the
calculation of total energies and related `mechanical' properties of materials
(an application to the structural properties of the mineral zincblende will be 
briefly discussed), the accurate prediction of electronic structures requires 
us to go beyond this  approximation. Two methods, the so-called GW technique 
(a kind of time-dependent Hartree-Fock theory) and Quantum Monte Carlo 
calculations will be introduced, and their application to a two-dimensional 
model crystal will be discussed.

                      Monday , September 25 1995
                           5:30 pm
                    Room 206, Science & Tech. I
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