A. Flores-Riveros

Approximate exchange energy as a functional of the electron density. Light atoms

We derive an expression for the exchange energy integral in terms of the density for the case of light atoms containing s and p electrons. We start from an approximate functional form of the density matrix for an electron cloud in the presence of an attractive nucleus. An important restriction to consider is the Pauli principle. A correction factor is included to account for the multipole expansion in an average way. The results we obtain, both for closed and open shells, are within a few percent of the exact exchange integral.

Atom-in-the-lattice description of Ce3+ impurity centers in alkaline-earth fluorides

Abstract We apply the Perturbed Ion method, amenable to the description of ionic crystal structures within an atom-in-the-lattice scheme, to analyze some electronic properties of Ce-doped BaF 2 and CaF 2 crystals. In addition, we compare with other ab initio molecular orbital methods for model clusters. We find that the most stable structure consists of a substitutional Ce 3+ combined with an interstitial F − to compensate the excess positive charge.

Ab initio calculations for absorption and emission energies of alkali halide crystals doped with thallium

The design of new materials capable of yielding optimal performance to detect radiation calls for a deeper theoretical understanding of luminescent properties arising from substitutional defects in solids. Here, the authors calculate transition energies associated with optical properties of thallium doping in alkali halide crystals via an atomic cluster of minimal size where an sp-valence-shell impurity enters as a substitutional defect in the model crystal. Hartree-Fock (HF), density functional theory (DFT), and configuration interaction (CI) [CIS (CI with single excitation) and QCISD (single plus double and quadruple excitation)] calculations are performed to theoretically obtain the absorption and emission energies as vertical transitions evaluated at the ground and first excited-state optimized geometries, respectively, where the optimization is carried out separately with the HF and DFT methods.