Mohammed Sahnoun

Full potential linearized augmented plane wave calculations of structural and electronic properties of GeC, SnC and GeSn

Abstract A theoretical study of structural and electronic properties of GeC, SnC and GeSn is presented using the full potential linearized augmented plane wave method. In this approach, the generalized gradient approximation was used for the exchange–correlation potential. Results are given for lattice constant, bulk modulus and its pressure derivative in both zinc-blende and rocksalt structures. Band structure, density of states and band gap pressure coefficients in zinc-blende structure are also given. The results are compared with previous calculations and with experimental measurements.

Prospecting Lighting Applications with Ligand Field Tools and Density Functional Theory: A First-Principles Account of the 4f7–4f65d1 Luminescence of CsMgBr3:Eu2+

The most efficient way to provide domestic lighting nowadays is by light-emitting diodes (LEDs) technology combined with phosphors shifting the blue and UV emission toward a desirable sunlight spectrum. A route in the quest for warm-white light goes toward the discovery and tuning of the lanthanide-based phosphors, a difficult task, in experimental and technical respects. A proper theoretical approach, which is also complicated at the conceptual level and in computing efforts, is however a profitable complement, offering valuable structure-property rationale as a guideline in the search of the best materials. The Eu(2+)-based systems are the prototypes for ideal phosphors, exhibiting a wide range of visible light emission. Using the ligand field concepts in conjunction with density functional theory (DFT), conducted in nonroutine manner, we develop a nonempirical procedure to investigate the 4f(7)-4f(6)5d(1) luminescence of Eu(2+) in the environment of arbitrary ligands, applied here on the CsMgBr3:Eu(2+)-doped material. Providing a salient methodology for the extraction of the relevant ligand field and related parameters from DFT calculations and encompassing the bottleneck of handling large matrices in a model Hamiltonian based on the whole set of 33,462 states, we obtained an excellent match with the experimental spectrum, from first-principles, without any fit or adjustment. This proves that the ligand field density functional theory methodology can be used in the assessment of new materials and rational property design.

Investigation of the electronic structure in La1?xCaxCoO3 (x = 0, 0.5) using full potential calculations

The electronic and magnetic properties of both LaCoO3 and La0.5Ca0.5CoO3 have been investigated by means of ab initio full-potential augmented plane wave plus local orbitals (APW+lo) calculations carried out with the Wien 2k code. The functional used is the local-density approximation LDA +U. Doping with Ca2+ introduces holes into the Co?O network. We analyse the densities of states and we confirm that the intermediate state?(IS) is stabilized by the Ca2+ substitution. This intermediate state in our results turns out to be metallic, and has a large density of states at the Fermi energy. The calculated magnetic moment in La0.5Ca0.5CoO3 is found to be in good agreement with experiment.

Wavelet investigation of La0.5Ca0.5CoO3−δ x-ray absorption data

Morlet wavelet transformation was used to analyze the Co K-edge extended x-ray absorption spectrum of La0.5Ca0.5CoO3−δ. Due to recent success in wavelet analysis of extended x-ray absorption fine structure (EXAFS) data we hoped that the Co–La scattering path could be separated from the Co–Ca scattering path in the EXAFS spectrum of La0.5Ca0.5CoO3−δ. The result showed a certain resolution of the wavelet transformed spectrum in the k space. Using theoretical scattering functions of the individual scattering paths calculated with ab initio multiple scattering codes (FEFF), it was possible to assign some maxima in the wavelet transformation EXAFS spectrum. The Co–La scattering path could be identified, but no additional information about the Co–Ca scattering function was obtained. A detailed analysis of the theoretical Co–La and Co–Ca scattering functions revealed that the two scattering functions overlap considerably in k space and have almost the same frequency. Morlet wavelet transformation of the sum of t...