DFT studies on electronic and structure properties of PbSe1-xSx alloys for thermoelectric materials using VCA and RS

We have performed a density functional theory (DFT) study of the electronic structure in ceria [Formula: see text] and gadolinium-doped ceria (GDC) system using VASP code in the generalized gradient approximation (GGA) with DFT[Formula: see text]+[Formula: see text]U. The band structures in GDC and thin film GDC are calculated and compared to that of bulk ceria. Doping of gadolinium significantly decreases the band gap of ceria, while the thin film structure of GDC raises the band gap greatly. The results help explain the electronic conductivity behavior of GDC and suggest that thin film-structured GDC could be used as a possible way to overcome the current leakage disadvantage of GDC.

Theoretical study of structural, electronic, optical and thermoelectric properties of XN (X = Sc, Y)

We report a combined anion photoelectron spectroscopy and density functional theory (DFT) study on a series of iron monoxide clusters, FenO (n=2–6). Well-resolved photoelectron spectra were obtained for FenO− at variable detachment energies, allowing the ground state and numerous low-lying excited states of FenO to be observed. Sharp threshold photoelectron features were obtained for each species, which suggest rather small geometry changes between the anion and neutral ground states for the monoxide clusters and allows the electron affinities of the neutral clusters to be measured accurately. Extensive DFT calculations using the generalized gradient approximation were carried out for both FenO and FenO−. Optimized geometries of the ground and lowest excited states of both the anion and neutral species are reported along with the ground-state vibrational frequencies and fragmentation energies. Theoretical electron affinities were compared with the experimental measurements to verify the ground states of the iron monoxide clusters obtained from the DFT calculations.

The electronic, thermoelectric, optical, and magnetic properties of the samarium aluminate (SmAlO3) compound is studied using the spin-polarized full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). The exchange and correlation potential is treated with the generalized gradient approximation (GGA) and the Coulomb repulsion ([Formula: see text] Ry) has been calculated theoretically and was used for the GGA[Formula: see text] based approximated electronic structures. Additionally, the modified Becke–Johnson (mBJ) potential was also utilized along with the GGA[Formula: see text] approach for the calculation of the band gap. On the other hand, the optical properties were analyzed with the mBJ[Formula: see text] results and the thermoelectric properties were explained on the basis of the electronic structures and density of states (DOS) with a thermoelectric efficiency of 0.66 at 300 K. The minimum reflectivity at 1.13 eV (which was equal to 1.097 [Formula: see text]m) was found to be in agreement with the experimental results. Further refinements in the electronic structures were obtained by adding the spin–orbit coupling (SOC) interactions to the GGA[Formula: see text] approach, which was then combined with the mBJ approximations. Hence, a conclusion using the combined mBJ[Formula: see text]SOC study indicates that the SmAlO3 compound is a potential candidate for both thermoelectric as well as magnetic devices.

Structural, electronic and thermal properties of AlxGa1−xAs ternary alloys: Insights from DFT study

We have studied the crystal structure of the AmCm binary alloy under high pressure by means of first-principles self-consistent total-energy calculations using the generalized gradient approximation (GGA) for the density functional theory (DFT). The virtual crystal approximation (VCA) is used for the description of the alloy system. In the present study, we investigated the double hexagonal (P63/mmc) structure, the face centered cubic (Fm3m) structure, the face-centered orthorhombic (Fddd) structure and the primitive orthorhombic (Pnma) structure for the AmCm alloy. Antiferromagnetic calculations have been compared with ferromagnetic calculations for all these phases. Our results are in general good agreement with recent experiment performed by Lindbaum et al. [J. Phys.: Condens. Matter. 15, S2297 (2003)].

First principles investigation of the structural, electronic, optical and elastic properties of [formula omitted]alloys

Pt electrocatalysts in high-temperature proton exchange membrane fuel cells (HT-PEMFCs) containing phosphoric acid (PA)-doped polymer membranes are prone to poisoning by leaked PA. We performed a preliminary density functional theory (DFT) study to investigate the relationship between the electronic structure of Pt surfaces and their adsorption of PA. Excess charge on Pt was found to weaken its bonding with the oxygen in PA, thus presenting a strategy for the fabrication of PA-resistant catalyst materials. Consequently, PtCu-alloy catalysts with various compositions were prepared by electrodeposition. The morphologies and crystalline structures of the alloys were strongly dependent on alloy composition. Moreover, the Pt atoms in the PtCu-alloy catalysts were found to be in an electron-rich state, similar to that of the excessively charged Pt simulated in the DFT study. As a result, the oxygen reduction reaction activities of the PtCu-alloy catalysts were superior to that of a Pt-only catalyst, regardless of the presence of PA. In the absence of PA, the higher activity of the PtCu-alloy catalysts was ascribable to conventional alloying effects, while the increased activity in the presence of PA was largely due to the enhanced resistance to PA poisoning. Therefore, PtCu-alloy catalysts easily prepared by electrodeposition were found to be strong candidate materials for HT-PEMFC electrodes.

Based on the pseudopotential scheme under the virtual crystal approximation in which the effect of compositional disorder is involved, the dependence of optoelectronic properties of GaAsxSb1-x on alloy composition x have been studied. Our results showed generally good agreement with the available experimental data. The material of interest is found to exhibit features of both direct and indirect band-gap semiconductor depending on the alloy composition x. The method used has been combined with the Harrison bond-orbital model and employed to calculate the dielectric constants and their composition dependence.

In this study, we report the electronic structure properties of SmFe2 and HoCo2 binary Laves phase compounds using the density functional theory (DFT) method. We treated the exchange correlation potential with generalized gradient approximation (GGA); in addition, GGA+U (U: Hubbard correction) calculations were applied to describe the correlation effects. At the equilibrium state, the lattice parameter [Formula: see text] is found in favorable agreement with the available data. We also treated the magnetic properties of SmFe2 and HoCo2, respectively; it is shown that the magnetic moment values of Sm and Ho atoms are larger than those of Fe and Ho elements. We note that the GGA with Hubbard correction (U) provides the best description of our systems. We also illustrated the band structures and total and partial densities of states (DOS) of the rare earth-4f (Sm and Ho) and transition metals-3d (Fe and Co) orbitals. For both approximations used, the SmFe2 and HoCo2 binary compounds have a metallic character at the Fermi level. This investigation shows the importance of the treatment of correlated electrons for a clear and accurate description of these binary compounds of the Laves phases family.

Motivated by the excellent thermoelectric (TE) performance of bulk SnSe, extensive attention has been drawn to the TE properties of the monolayer SnSe. To uncover the fundamental mechanism of manipulating the TE performance of the SnSe monolayer, we perform a systematic study on the TE properties of five monolayer SnSe allotropes such as α-, β-, γ-, δ-, and ε-SnSe based on the density functional theory and the non-equilibrium Green’s functions. By comparing the TE properties of the Na-doped SnSe allotropes with the undoped ones, the influences of the Na doping and the temperature on the TE properties are deeply investigated. It is shown that the figure of merit ZT will increase as the temperature increases, which is the same for almost all the Na-doped and undoped cases. The Na doping can enhance or suppress the ZT in different SnSe allotropes at different temperatures, implying the presence of the anomalous suppression of the ZT. The Na doping induced ZT suppression may be caused basically by the sharp decrease of the power factor and the weak decrease of the electronic thermal conductance, rather than by the decrease of the phononic thermal conductance. We hope this work will be able to enrich the understanding of the manipulation of TE properties by means of dimensions, structurization, doping, and temperature.

Ternary adsorption of Auramine-O, Rhodamine 6G, and Brilliant Green onto Arapaima gigas scales hydroxyapatite: Adsorption mechanism investigation using CCD and DFT studies

The monoclinic L-histidine crystal is critical for protein structure and function and is also found in the myelin of brain nerve cells. This study numerically examines its structural, electronic, and optical properties. Our findings indicate that the L-histidine crystal has an insulating band gap of approximately 4.38 eV. Additionally, electron and hole effective masses range between 3.92[Formula: see text]-15.33[Formula: see text] and 4.16[Formula: see text]-7.53[Formula: see text], respectively. Furthermore, our investigation suggests that the L-histidine crystal is an excellent UV collector due to its strong optical absorption activity for photon energies exceeding 3.5 eV. To investigate the structural, electronic, and optical properties of L-histidine crystals, we used the Biovia Materials Studio software to conduct Density Functional Theory (DFT) simulations as implemented in the CASTEP code. Our DFT calculations were performed using the generalized gradient approximation (GGA) as parameterized by the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional, with an additional dispersion energy correction (PBE [Formula: see text] TS) based on the model proposed by Tkatchenko and Scheffler to describe van der Waals interactions. Additionally, we employed the norm-conserving pseudopotential to treat core electrons.

The optoelectronics performances of two-dimensional Cu-doped SnO2 nanosheets were investigated by first-principles calculations on the basis of density functional theory (DFT) and experiments. First, the crystal structures of Cu-doped SnO2 were built and analyzed by using DFT within the generalized gradient approximation (GGA). The total energy of Cu-doped SnO2 was discussed qualitatively and quantitatively from three aspects: charge density, band structure, and state density. The results show that copper doping has little effect on the charge density distribution because of the similar ionic radius of Cu2+, Sn4+, and the close bond lengths of Cu–O and Sn–O. The calculation results of band structure and state density show that the doping of a copper acceptor leads to the appearance of a new energy level at the top of the valence band and decreases the band gap of SnO2. With the guidance of theoretical calculation, the nanosheets of Cu-doped SnO2 are constructed experimentally, and their optoelectronics performances are investigated. The experimental results exhibit that the Cu atom replaces the Sn atom in the SnO2 lattice, while the Cu-doped SnO2 retains the original rutile phase of the intrinsic SnO2. The sample with a doping ratio of 12.5% has more uniform particle morphology and dispersion characteristics. In addition, the 12.5% Cu-doped SnO2 obtained the largest transient photocurrent of 3 μA/cm2 and the lowest resistance to charge transfer, thereby indicating that the material has a remarkably higher optoelectronics performance under this ratio. The theoretical calculation and experimental results are consistent, which indicates that Cu doping effectively enhances the charge transfer in SnO2 and enables it for high-quality application in optoelectronic catalysis.

Computational calculations based on density functional theory were carried out to investigate ferromagnetism in gallium arsenide (GaAs) heavily doped with Fe atoms that can substitutionally occupy gallium (Ga) or arsenic (As) sites in the zinc-blende-like crystal structure. The calculations were performed within the spin polarized density functional theory (DFT) and generalized gradient approximation (GGA) with full potential linearized augmented plane wave (FP-LAPW) method. We investigate and discuss the ab initio calculation results focusing on properties intrinsically important for spintronic applications, such as spin polarization and magnetic anisotropy. The density of states (DOS) was calculated with substitution of Fe atoms in the As and Ga sites, giving the electronic properties, as well as the magnetic ground state. According to DFT calculations, heavily doped GaAs with 25 at. % of Fe becomes a ferromagnetic metal with spin polarization as high as 69% at Fermi level. This is corroborated by experimental results previously published in literature.