CsPd0.875Cr0.125I3 Promising Candidate for Thermoelectric Applications

We study the electronic structure, magnetization, and thermoelectric properties of CsPd0.875Cr0.125I3 obtained by doping CsPdI3 with atoms of the 3d transition metal Cr. By applying the generalized-gradient-approximation (GGA) and the GGA + U one, we found that CsPd0.875Cr0.125I3 alloy exhibits a completely metallic characteristic. Changes in the thermoelectric properties of the alloy are determined with the use of the BoltzTrap code. The electronic thermal conductivities (k/т), Seebeck coefficients (S), power factors (PF), and electrical conductivities (q/т) are calculated. The value of the ZT merit factor is near 1 at room temperature, by indicating that CsPd0.875Cr0.125I3 is a good candidate for thermoelectric applications at high and low temperatures.

Electronic structure and Thermoelectric Properties of Hybrid Organic-Inorganic Perovskites [NH3-(CH2)3-COOH]2CdCl4

In this work, we conducted the first principle calculation of electronic structure and transport properties of [NH3-(CH2)3-COOH]2CdCl4 (Acid-Cd). The generalized gradient approximation is used in structural optimization and electronic structure. The theoretical band gap value found is in good agreement with experimental. Electronic thermal conductivity, electrical conductivity, Seebeck coefficient (S) and figure of merit (ZT) have been calculated using semi-local Boltzmann theory to predict the thermoelectric characteristic of the studied materials.

Surface energies and relaxation of NiCoCr and NiFeX (X=Cu, Co or Cr) equiatomic multiprincipal element alloys from first principles calculations

First principles calculations of the energies and relaxation of unreconstructed low-index surfaces, i.e. (001), (011) and (111) surfaces, in NiCoCr and NiFeX (X=Cu, Co or Cr) equiatomic multi-principal element alloys are presented. The calculations were conducted for twelve-layer slabs represented by special quasi-random supercells using the projector augmented wave method within the generalized gradient approximation. While experimental predictions are unavailable for comparison, the calculated surface energies agree fairly well with those from thermodynamic modeling and a bond-cutting model. In addition, the calculations unveil an important surface structure, namely, that the topmost surface layer is in contraction except for the (001) surface of NiFeCr alloy, the next layer below is in extension, and the bulk spacing is gradually recovered from the subsequent layers down. Additionally, the surface contraction is the most pronounced on the (011) plane, being about 4-10% relative to the bulk spacings. The results presented here can provide an understanding of surface-controlled phenomena such as corrosion, catalytic activities and fracture properties in these equiatomic multi-principal element alloys.

Performances of different DFT functionals to calculate the anodic limit of fluorinated sulphonyl-imide anions for lithium cells

In this paper we investigated the calculation of the anodic limit of two anions of ionic liquids, largely used as electrolyte of lithium batteries. Starting from a model based on calculations performed on single ions at the MP2 level of theory, we showed that the matching between calculation and experiments decreases while using more expanded basis set with respect to 6-31G**, possibly because of the destabilization of the neutral species when larger basis sets are considered. Additionally, in order to decrease the computational time, the performances for the calculation of the anodic limit obtained by means of a series of DFT functionals with increasing level of complexity (from the Generalized Gradient Approximation to the Range Separated Hybrid meta-Generalized Gradient Approximation) were compared. Overall, the best performing functionals are BMK, ωB97M-V and MN12-SX, while acceptable results can be obtained by M06-2X, M11, M08-HX and M11-L. Some less computationally expensive functionals, like CAM-B3LYP and ωB97X-D, also provide reasonable values of the anodic limit.

Theoretical investigations on structural and optoelectronic properties of Bismuth oxyhalides

Density functional theory’s (DFT) full potential linearized augmented plane wave method has been used to explore the structural and optoelectronic properties of bismuth-based tetragonal BiOCl, BiOBr and BiOI semiconductors. The generalized gradient approximation (GGA) has been used for structural optimization to approximate lattice constants and bulk moduli, which are found to be consistent with the current literature. Electronic band structures are computed using the modified Becke and Johnson generalized gradient approximation (mBJ) and within the Engel and Vosko generalized gradient approximation (EV-GGA), respectively. Based on the band structure analysis, these functional materials are indirect bandgap semiconductors with a wide range of potential applications. In addition, optical properties are also computed within mBJ and found to be appealing for optoelectronics and photocatalysis.

The Structural, Elastic, Electronic, Vibrational and Gravimetric Hydrogen Capacity Properties of the Perovskite Type Hydrides: DFT Study

The structural, elastic, anisotropic elastic, electronic, vibrational and properties of the Perovskite type Hydrides RbXH3 (X = Be, Ca, Mg) were performed via Vienna Ab – initio Simulation Pac-kage (VASP) based on Density Functional Theory (DFT). Our results have exhibited a well-agreement with previous calculations and experiments for each compound. In order to de-termine physical properties of RbXH3 has been used the Generalized Gradient Approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) functional at this study. Present compounds were found to be mechanically stable as well as their gravimetric hydrogen storage capacities has been investigated. The Perovskite type Hydrides RbBeH3 and RbMgH3 has an indirect bandgap of 0.274 eV and 2.209 eV while RbCaH3 has a direct bandgap of 3.274 eV respectively and therefo-re these compounds has shown a semiconductor behaviour at equilibrium. Besides directional dependence of anisotropic properties was visualized by representing them with maximum - mi-nimum points..

New polymorphic varieties of boron nitride with graphene-like structures

First-principle calculations of the structure and electronic properties of four new polymorphic varieties of graphene-like boron nitride, the structure of which is similar to the structure of graphene polymorphs, the atoms in which are in the spirit of different structural positions, were performed by the density functional theory method in the generalized gradient approximation. As a result of the studies carried out, the possibility of stable existence of three monoatomic boron nitride layers: BN-L4-6-8a, BN-L4-6-8b and BN-L4-10 has been established. The BN-L4-12 layer is transformed into the BN-L4-6-8 layer during geometric optimization. The lengths of interatomic bonds in boron nitride monolayers vary in the range 1.4353 Å ÷ 1.4864 Å, and the bond angles in the range 84.05° ÷ 152.26°. The band gap of the BN layers varies from 3.16 eV to 3.90 eV. Sublimation energies are in the range from 16.67 eV/(BN) to 17.61 eV/(BN).