Local-orbital basis for defect electronic structure calculations of an Al(100) film

Preliminary to performing first-principles scattering-theory calculations of adsorbate and defect properties on Al(100), a linear combination of atomic orbitals (LCAO) basis of 53 rather short-ranged contractions of Gaussians has been constructed which reproduces the electronic level structure of a well-converged linearized augmented-plane-wave (LAPW) calculation for a five-layer Al(100) film to better than 0.15 eV. Using this basis, a scattering-theory evaluation of the force on a single surface Al atom of an ideal film shows it to be inward and equal to about 0.02 eV/bohr. A search for the outer Al layer height at which this force vanishes implies a slight reduction of the outer-layer separation, about 0.25%. This result also agrees with the LAPW result. Neither spectroscopic nor geometric LCAO results agree well with those of the LAPW if d-like Al-centered orbitals are not included in the LCAO basis.