Characterization of BAND

• Functionality
• Analysis
• Technical

Functionality

• Formation energy with respect to isolated atoms that are computed with a fully numerical Herman-Skillman type subprogram
• A choice of density functionals, including LDA (Local Density Approximation) and GGA (Generalized Gradient Approximation) formulas
• Automatic geometry optimization has not yet been implemented

Analysis

• Mulliken populations for basis functions, overlap populations between atoms or between basis functions.
• Densities-of-States: DOS, PDOS and OPWDOS/COOP
• Form factors (X-ray structures)
• Charge analysis using Voronoi cells (yielding Voronoi Deformation Charges)
• Orbital plots
• One-electron energies and orbitals at the Brillouin Zone sample points
• Fragment orbitals and a Mulliken type population analysis in terms of the fragment orbitals

Technical

• SCF convergence based on a Direct Inversion of Iterative Subspace (DIIS) method
• The implementation is built upon a highly optimized numerical integration scheme for the evaluation of matrix elements of the Hamiltonian, property integrals involving the charge density, etc.
• The program has been parallelized and vectorized
• Basis functions are Slater-Type Orbitals (STOs) and/or Numerical Orbitals (NOs) and/or Plane Waves (PWs).
• Fit functions are Slater-type exponential functions centered on the atoms and are used to fit the deformation density, which is the difference between the final density and the startup density. The deformation density has zero charge and will in general be small. The fitted deformation density is used for the calculation of the Coulomb potential and the derivatives of the total density (needed for the gradient corrections in the exchange-correlation functionals). In both cases the main part, due to the startup density, is calculated accurately by a numerical procedure, and only the small part from the deformation density is obtained via the fit.
• A frozen core facility is provided to allow efficient treatment of the inner atomic shells.
• Space group symmetry is used to reduce the computational effort in the integrals over the Brillouin zone.