Further developments in the local-orbital density-functional-theory tight-binding method - art. no. 195103

Improvements to the Sankey-Niklewaki method [O. F. Sankey and D. J. Niklews ki, Phys. Rev. B 40, 3979 1989)] for computing total energies and forces, w ithin an ab initio tight-binding formalism, are presented here. In particul ar, the improved method (called FIREBALL) uses the separable pseudopotentia l (Hamann or Troullier) and goes beyond the minimal sp(2) basis set of the Sankey-Niklewski method, allowing for double numerical basis sets with the addition of polarization orbitals and d orbitals to the basis set. A major improvement includes the use of more complex exchange-correlation functiona ls, such as Becke exchange with the Lee-Yang-Parr correlation. Results for Cu and GaN band structures using d orbitals within the improved method are reported, the results for GaN are greatly improved compared to the minimal basis results. Finally, to demonstrate the flexibility of the method, resul ts for the H2O dimer system and the energetics of a gas-phase octahydro-1,3 ,5,7-tetranitro-1,3,5,7-tetrazocine molecule are reported.