Reconstruction of Nonpolar GaN Surfaces
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METHOD The interatomic potentials and forces for molecular dynamics are derived by a densityfunctional based non-orthogonal tight-binding scheme. As has been recently described in detail in the literature [2], the Kohn-Sham orbitals of the many-atom structure are represented by a linear combination of atomic orbitals (LCAO)-Ansatz, where we use the localized valence electron orbitals as a minimal basis. Within a two-center approach all Hamilton and overlap matrix elements are derived in a parameter free way via the construction of pseudo-atomic orbitals and potentials by self-consistent single-atom calculations on the LDA level. This two-center approach enables us to tabulate the corresponding Slater-Koster integrals versus interatomic distance. We then perform a non-self consistent solution of the Kohn-Sham equations for the many-atom structure in order to determine the electronic energy and finally derive a universal short-range repulsive pair potential with respect to scf-LDA results. The total energy of the system can then be written in the usual tight-binding form as a sum of the electronic band-structure energy (sum over all occupied Kohn-Sham energies ci) and the repulsive energy: Ett({Rk})
=
EBs({Rk}) + Erp({QRk
= Z--Q({Rk}) + Z i
k
-
RiI})
,-Vrp(IR1 - Rki) •
(1)
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