Diola Bagayoko

Misconceptions and the Certainty of Response Index (CRI).

We describe a simple and novel method for identifying misconceptions. This approach utilizes the Certainty of Response Index (CRI) in conjunction with answers to multiple choice questions.

Ab initio calculations of the electronic structure and optical properties of ferroelectric tetragonal

The electronic structure, charge distribution, effective charge, and charge transfer in ferroelectric tetragonal are carefully studied using a local density functional potential and a self-consistent ab initio LCAO (linear combination of atomic orbitals) method. It is shown that the band gap and low-energy conduction band can be calculated with a reasonable accuracy when the ab initio LCAO method is used with an optimum basis set of atomic orbitals. The calculated optical spectrum, band gap, and effective mass of , obtained from the calculated electronic structure, are in good agreement with experimental results.

Predictions of electronic, structural, and elastic properties of cubic InN

We present theoretical predictions of electronic, structural, and elastic properties of cubic indium nitride in the zine-blende structure (c-InN). Our ab initio, self-consistent calculations employed a local density approximation potential and the Bagayoko, Zhao, and Williams implementation of the linear combination of atomic orbitals. The theoretical equilibrium lattice constant is 5.017A, the band gap is 0.65eV, and the bulk modulus is 145GPa. The band gap is 0.74eV at an experimental lattice constant of 4.98A.

Ab-initio Electronic and Structural Properties of Rutile Titanium Dioxide

Ab-initio, self-consistent electronic energy bands of rutile TiO2 are reported within the local density functional approximation (LDA). Our first principle, non-relativistic and ground state calculations employed a local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). Within the framework of the Bagayoko–Zhao–Williams (BZW) method, we solved self-consistently both the Kohn–Sham equation and the equation giving the ground state charge density in terms of the wave functions of the occupied states. Our calculated band structure shows that there is significant O 2p–Ti 3d hybridization in the valence bands. These bands are well separated from the conduction bands by an indirect band gap of 2.95 eV, from Γ to R. Consequently, this work predicts that rutile TiO2 is an indirect band gap material, as all other gaps from our calculations are larger than 2.95 eV. We found a slightly larger, direct band gap of 3.05 eV, at the Γ point, in excellent agreement with experiment. Our calculations reproduced the peaks in the measured conduction and valence bands densities of states, within experimental uncertainties. We also calculated electron effective mass. Our structural optimization led to lattice parameters of 4.65 and 2.97 A for a0 and c0, respectively with a u parameter of 0.3051 and a bulk modulus of 215 GPa.

Density-functional theory band gap of wurtzite InN

We report the calculated band gap of wurtzite indium nitride. Our ab initio computations employed a local-density approximation (LDA) potential and the linear combination of Gaussian orbital formalism. The implementation of the ab initio Bagayoko, Zhao, and Williams method [Phys. Rev. B 60, 1563 (1999)] led to a LDA band gap of 0.88eV, in excellent agreement with recent experiments. We also present calculated density of states (DOS) and the electron effective mass at the bottom of the conduction band. Our DOS curves indicate that an experiment could find values of the band gap up to 2eV, depending on the sensitivity of the apparatus, the interpretation of resulting data, and associated uncertainties.

Understanding density functional theory (DFT) and completing it in practice

We review some salient points in the derivation of density functional theory (DFT) and of the local density approximation (LDA) of it. We then articulate an understanding of DFT and LDA that seems to be ignored in the literature. We note the well-established failures of many DFT and LDA calculations to reproduce the measured energy gaps of finite systems and band gaps of semiconductors and insulators. We then illustrate significant differences between the results from self consistent calculations using single trial basis sets and those from computations following the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). Unlike the former, the latter calculations verifiably attain the absolute minima of the occupied energies, as required by DFT. These minima are one of the reasons for the agreement between their results and corresponding, experimental ones for the band gap and a host of other properties. Further, we note predictions of DFT BZW-EF calculations that have been...

Electronic structure and charge transfer in 3C- and 4H-SiC

We utilized a local density functional potential, the linear combination of atomic orbital (LCAO) method, and the BZW procedure to study the electronic structure of 3C- and 4H-SiC. We present the calculated energy bands, band-gaps, effective masses of n-type carriers, and critical point transition energies. There is good agreement between the calculated electronic properties and experimental results. Our preliminary total energy calculations for 3C-SiC found an equilibrium lattice constant of a = 4.35 A, which is in agreement with the experimentally measured value of 4.348 A. The calculated charge transfers indicate that each silicon atom loses about 1.4 electrons that are gained by a carbon atom in both 3C- and 4H-SiC.

Band structure, optical properties, and compton profile of copper

Abstract A self-consistent calculation of the band structure of copper has been performed using a basis of gaussian orbitals and a local exchange-correlation potential. Results are also presented for the optical conductivity and the Compton profile.

First principle electronic, structural, elastic, and optical properties of strontium titanate

We report self-consistent ab-initio electronic, structural, elastic, and optical properties of cubic SrTiO3 perovskite. Our non-relativistic calculations employed a generalized gradient approximation (GGA) potential and the linear combination of atomic orbitals (LCAO) formalism. The distinctive feature of our computations stem from solving self-consistently the system of equations describing the GGA, using the Bagayoko-Zhao-Williams (BZW) method. Our results are in agreement with experimental ones where the later are available. In particular, our theoretical, indirect band gap of 3.24 eV, at the experimental lattice constant of 3.91 A, is in excellent agreement with experiment. Our predicted, equilibrium lattice constant is 3.92 A, with a corresponding indirect band gap of 3.21 eV and bulk modulus of 183 GPa.

Calculated optical properties of wurtzite InN

We report ab initio, self-consistent calculations of the dielectric function of wurtzite indium nitride (w-InN). Our calculations employed a local density approximation (LDA) potential, a linear combination of atomic orbital basis set, and the Bagayoko-Zhao-Williams (BZW) method. Our findings agree very well with recent measurements up to photon energies of 6eV. This excellent agreement shows the correct description, by the LDA-BZW method, of the relative separations between upper valence bands and low-lying conduction bands, in general, and corroborates our previous result of 0.88eV for the intrinsic, fundamental band gap of w-InN, in particular. We also report results of simulations of the effect of high electron doping on the optical properties of InN.