Specific features of electronic structure and linear optical properties of some pseudocubic compounds

Ab-initio calculation of structural, electronic, and optical characterizations of the intermetallic trialuminides ScAl 3 compound

First principles study of three dimensional topological phases of GdxY1−xPtBi (x=0, 0.25, 0.5, 0.75, 1) alloys

The electronic properties and topological phases of ThXY (X = Pb, Au, Pt, Pd and Y = Sb, Bi, Sn) compounds in the presence of spin–orbit coupling, using density functional theory are investigated. The ThPtSn compound is stable in the ferromagnetic phase and the other ThXY compounds are stable in nonmagnetic phases. Band structures of these compounds in topological phases (insulator or metal) and normal phases within generalized gradient approximation (GGA) and Engel–Vosko generalized gradient approximation (GGA_EV) are compared. The ThPtSn, ThPtBi, ThPtSb, ThPdBi, and ThAuBi compounds have topological phases and the other ThXY compounds have normal phases. Band inversion strengths and topological phases of these compounds at different pressure are studied. It is seen that the band inversion strengths of these compounds are sensitive to pressure and for each compound a second-order polynomial fitted on the band inversion strengths–pressure curves.

Photo-induced treatment of l-alanine single crystals grown by slow evaporation method at an ambient temperature was performed using a 25 ps Nd:YAG pulsed laser in the presence of an external acoustic filed. The changes of the absorption were studied for the wavelength 265 nm near the energy band gap edge at acoustical power density varying within 4–6 W/cm2. The observed absorption changes indicate that the external optical electric field strengths and acoustical power densities may be efficient parameters for the characterization of photo-optical and acousto-optical treatment of the samples. From the X-ray diffraction data we have optimized the atomic positions assuming that force on the atoms is around 1 mRy/au. These are used to calculate the electronic structure and the chemical bonding for the amino acid l-alanine single crystals. The calculated electronic band structure and densities of states confirms the experimental results that this compound possesses a relatively large energy band gap. The upper valence band has its maximum at the Z point of the Brillouin zone while the conduction band minimum is located at Γ point in the zone center, resulting in an indirect energy band gap. The electronic energy gap is equal to 4.19 eV within a framework of the used local density approximation and 4.54 eV with the Engel–Vosko generalized gradient approximation as the exchange correlation potential. This is in an agreement with our experimentally measured energy band gap ~4.67 eV. The existence of O-p character in the upper valence band has a significant consequence for the optical band gap. From our calculated electron charge density distribution, we obtain a space electron charge density distribution in the average unit cell of the crystal. The chemical bonding features of l-alanine amino acid were analyzed.

FP-LAPW investigation of structural, electronic, linear and nonlinear optical properties of ZnIn 2Te 4 defect-chalcopyrite

Optical properties of some laves phases compounds

The optical dielectric functions for single-crystal ${\mathrm{KTaO}}_{3}$ are determined using spectroscopic ellipsometry and optical transmission techniques. These results show that the lowest band gap is $3.64\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ $(341\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ with very low absorption up to $4.28\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, indicating an indirect band gap. The ellipsometry results are analyzed using critical point analysis, which shows that there are three direct gaps at 4.35, 4.68, and $5.03\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The results are compared with band structure calculations determined using the local density approximation (LDA) and the Engel-Vosko generalized gradient approximation (GGA).

Engel-Vosko GGA calculations of the structural, electronic and optical properties of LiYO2

Electronic structure of REFe2 (RE = Dy, Ho and Er) intermetallic compounds: Ab initio spin-density functional theory

Using first‐principle calculations, a new compound semiconductor based on titanium (Ti) is predicted. It has been observed that Ti when alloyed with germanium (Ge) can crystallize in the zincblende symmetry, and exhibits semiconducting nature with a narrow bandgap. To test the robustness of the semiconducting nature, the structural properties and electronic band structure have been modeled using three different exchange–correlation functionals, namely, local density approximation, generalized gradient approximation, and Perdew‐Burke‐Ernzerhof for solids. With a nominal composition of 1:1, TiGe exhibits a direct bandgap of 0.58 eV at the “X” point of the Brillouin zone. From lattice dynamics, the structural stability of the compound has been established. The new semiconductor is characterized in detail for its electronic band structure, carrier effective mass, charge density distribution, and linear optical properties. Zb‐TiGe exhibits large effective mass for conduction band holes and tentatively becomes a prototype system to study heavy holes resulting in carrier condensation at the bottom of the conduction band. The linear optical properties of the TiGe are found to be suitable for photosensitive devices in the infrared region. In addition, TiGe may find application in deep‐UV and far‐UV regions because of the surface plasmon resonance at 6.4 eV.

The Perdew, Burke and Ernzerhof (PBE) generalized gradientapproximation (GGA) is the most popular exchange-correlation energyused in today's ab initio studies. The GGA is tested here inrelation to the intrinsic uncertainty in choosing the degree oflocalization of the exchange-correlation hole (theκ-coefficient in the spin-polarized enhancement factor). Theproposed and most commonly used value of κ = 0.804 (best suitedfor atoms and molecules) works well for some solids but should bemodified in many cases in order to predict lattice parameters ingood agreement with experiments. The effect on the structural andmagnetic properties of 3d, 4d and 5d metals including the structuralphase order of Fe is examined using two different state-of-the-artab initio implementations of density functional theory: thefull-potential linearized muffin-tin orbital and full-potentiallinearized augmented-plane-wave methods. This study gives examplesfor the case of elemental d metals of the errors associated withthese properties when using the PBE-GGA in state-of-the-art ab initio electronic structure studies.

Vacancy formation energies in metals: A comparison of MetaGGA with LDA and GGA exchange–correlation functionals

Based on the density functional theory and first-principal calculations, the physical properties of the Zr3GeO8 crystal for the ground state were calculated. In all calculations, the Density functional theory based ABINIT package program was used. Investigations were made under the local density approximation. The geometric optimization of the Zr3GeO8 crystal, the state density of the valence electrons, the electronic band structure to understand the conductivity character of the crystal, and the linear optical properties to see the response of the material to the electromagnetic wave were calculated. In addition, dynamic-thermodynamic properties were calculated for the Zr3GeO8 crystal. According to the calculated structural optimization and electronic band structure, the band gap of the Zr3GeO8 crystal is 4.4663 eV and it has been obtained that it has an indirect band gap. For the Zr3GeO8 crystal, some constants such as energy loss functions, reflectivity, and absorption coefficient are calculated depending on the ground state linear optical properties and linear optical properties. The phonon distribution, state density and contribution of each atom to the density of state the Zr3GeO8 crystal were calculated. Finally, free energy, internal energy, entropy, and heat capacity were calculated for the Zr3GeO8 crystal.

We have developed a new set of norm-conserving pseudopotentials and companion Gaussian basis sets for the actinide (An) series (Ac - Lr) using the Goedecker, Teter and Hutter (GTH) formalism with the Perdew, Burke and Ernzerhof (PBE) exchange-correlation functional of generalized gradient approximation (GGA). To test the accuracy and reliability of the newly parameterized An-GTH pseudopotentials and basis sets, a variety of benchmarks on actinide-containing molecules are carried out and compared to all-electron and available experimental results. The new pseudopotentials include both medium- ([Xe]4f14) and large-core ([Xe]4f145d10) options that have successfully reproduced structures and energetics, particularly redox processes. The medium-core size set, in particular, reproduce all-electron calculations over multiple oxidation states from 0 to VII, whereas the large-core set is suitable only for the early series elements and low oxidation states. The underlying reason for these transferability issues are discussed in detail. This work fills a critical void in the literature for studying the chemistry of 5f-block elements in condensed phase.

Optical properties of the alkaline-earth fluorohalides matlockite-type structure SrFX (X=Cl, Br, I) compounds