Berkeley Lab Scientific Computing Seminar

Date:

Friday, May 25, 2007

Time:

1:00pm-2:00pm

Location:

Building 50A-5132

Seminar Speaker:

Eric Cances
CERMICS - ENPC
France
http://cermics.enpc.fr/~cances/home.html

Title:

Density functional theory for local defects in crystalline materials

Abstract:

Describing the electronic state of crystals with local defects is a major issue in solid-state physics, materials science and nano-electronics. Usually, the energy of a local defect is computed by subtracting the energy of the perfect crystal from the energy of the crystal with the defect, using a supercell model. However, the supercell model has several drawbacks. First, the defect interacts with its periodic images. Second, the supercell must have a neutral total charge, so that in the simulation of charged defects, an artificial charge distribution (a jellium for instance) needs to be introduced to counterbalance the charge of the defect. These two drawbacks may lead to large, uncontrolled, errors in the estimation of the energy of the defect. In practice, ad hoc corrections terms are introduced to account for these two sources of error.

In a recent article (E.C., A. Deleurence, E. Cances, 2007), we have used rigorous thermodynamic limit arguments to derive a model allowing to directly compute the perturbation of the electronic first order density matrix generated by a (neutral or charged) local defect, when the host crystal is an insulator or a semi-conductor. This model has a mathematical structure similar to that of the Chaix-Iracane model for the quantum electrodynamical description of atoms and molecules. This similarity originates from formal analogies between the Fermi sea of a perturbed crystal and the Dirac sea in presence of atomic nuclei.

Sponsor of Seminar:

Juan Meza

Scientific Computing

Contact Esmond G. Ng EGNg@lbl.gov