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In this work, we delve into the investigation of the structural, electronic, and optical properties of Ba2NbBiS6 and Ba2TaSbS6 chalcogenide-based double perovskites, which are structured in the cubic space group Fm3̄m form. We have performed first-principles calculations using density functional theory (DFT) to study the above properties. The electronic band structure and density of states of this compound have been investigated, and their results show that Ba2NbBiS6 and Ba2TaSbS6 exhibit a semiconducting nature with an indirect energy gap of 1.680eV and 1.529eV, respectively. Furthermore, an investigation was conducted on the optical properties of the compounds throughout the energy range spanning from 0eV to 55eV. This investigation focused on many parameters, including dielectric functions, optical reflectivity, refractive index, extinction coefficient, optical conductivity, and electron energy loss. The optical data obtained from the calculations reveals that all compounds demonstrate isotropy in optical polarization. Furthermore, it has been noted that our compounds exhibit absorption properties inside the ultraviolet (UV) region. Consequently, these materials hold promise as potential candidates for various applications, such as UV photodetectors, UV light emitters, and power electronics. This is primarily attributed to their inherent absorption limits and the presence of prominent absorption peaks in this spectral range. In brief, chemical mutation techniques have been employed to manipulate the characteristics of double-sulfide perovskites to develop durable and environmentally friendly perovskite materials suitable for solar purposes. [ABSTRACT FROM AUTHOR]

This study employs ab initio calculations based on density functional theory (DFT) to investigate the structural properties, 1H-NMR spectra, and vibrational spectra of methane sulfonic acid (MSA) at low degree of hydration. The findings reveal that energetically stable structures are formed by small clusters consisting of one or two MSA molecules (m = 1 and 2) and one or two water molecules in (MSA)m·(H2O)n (m = 1–2 and n = 1–5).These stable structures arise from the formation of strong cyclic hydrogen bonds between the proton of the hydroxyl (OH) group in MSA and the water molecules. However, clusters containing three or more water molecules (n > 2) exhibit proton transfer from MSA to water, resulting in the formation of ion-pairs composed of CH3SO3− and H3O+species. The measured 1H-NMR spectra demonstrate the presence of hydrogen-bonded interactions between MSA and water, with a single MSA molecule interacting with water molecules. This interaction model accurately represents the hydrogen bonding network, as supported by the agreement between the experimental and calculated NMR chemical shift results. [ABSTRACT FROM AUTHOR]

To study the structural properties of X2Se2C (X = Ta, Nb) MXenes, we have used an FP-LAPW method based on functional density theory GGA-PBE-sol, which is based on the method of plane waves increased by linear waves at full potential. From the most stable state, we determined other properties such as electronic, optical, and mechanical ones. Band structure calculations reveal the metal character of GGA. MXenes exhibit hexagonal crystal structures at zero temperature. Calculated elastic constants show the alloy's mechanical stability and ductility. Due to its high elasticity anisotropy, the alloy possesses excellent tensile strength. The dielectric function, absorption, reflectance, optical conductivity, and other optical properties were also investigated. In the ultraviolet region, X2Se2C (X = Ta, Nb) is an effective absorber and has a high refractive index. The projected density of state (PDOS) of (a) Nb2Se2C and (b) Ta2Se2C. [ABSTRACT FROM AUTHOR]

Electronic band structure, optical and thermodynamic properties of ternary hydrides MBe[H.sub.3] (M = Li, Na, and K) were studied using ab initio density functional theory (DFT). The effect of the adopted approximation to the exchange-correlation functional of the DFT is explicitly investigated by considering four different expressions of two different classes (local-density approximation and generalized-gradient approximation). The calculated magnitude of B classifies MBe[H.sub.3] (M = Li, Na, and K) as easily compressible materials. The bonding interaction in these compounds is quite complicated. The interaction between M and Be[H.sub.6] is ionic and that between Be and H comprises both ionic and covalent characters. The electronic structure of the complex hydride was investigated by calculating the partial and total densities of states, and electron charge density distribution. Large gaps in the density of states appear at the Fermi energy of LiBe[H.sub.3], NaBe[H.sub.3], and KBe[H.sub.3] indicating that these classes of hydrides are insulators. Optical properties, including the dielectric function, reflectivity, and absorption coefficient, each as a function of photon energy, are calculated and show an optical anisotropy for LiBe[H.sub.3] and KBe[H.sub.3]. Through the quasi- harmonic Debye model, in which the phononic effects are considered, temperature dependence of volume V(T), bulk modulus B(T), and thermal expansion coefficient α(T), constant-volume and constant-pressure specific heat ([C.sub.v] and [C.sub.p]) and Debye temperature [ϴ.sub.D], the entropy S, and the Gruneisen parameter γ were calculated at wide pressure and temperature ranges. The principal aspect of the obtained results is the close similarity of MBe[H.sub.3] (M = Li, Na, and K) compounds. Key words: electronic structure, crystal structure, hydrides, thermodynamic properties, reflectivity, absorption coefficient. Nous utilisons la methode ab initio de la fonctionnelle de densite (DFT) pour etudier la structure des bandes electroniques et les proprietes optiques et thermodynamiques d'hydrides ternaires MBe[H.sub.3] (M = Li, Na et K). Nous etudions systematiquement l'effet de l'approximation adoptee pour la fonctionnelle DFT d'echange-correlation, en considerant quatre differentes expressions de deux classes differentes: l'approximation locale de densite et l'approximation de gradient generalise. La magnitude calculee de B classe ces hydrides parmi les materiaux compressibles. L'interaction de liaison dans ces composes est tres compliquee. L'interaction entre M et Be[H.sub.6] est ionique, alors qu'elle est partiellement ionique et partiellement covalente entre Be et H. La structure electronique est investiguee en calculant la densite partielle et totale d'etats et la distribution de densite de charge electronique. De larges bandes interdites (gaps) apparaissent a l'energie de Fermi pour les trois hydrides, ce qui les classe parmi les isolants. Les proprietes optiques, incluant la fonction dielectrique, la reflectivite et le coefficient d'absorption sont calculees en fonction de l'energie du photon et nous observons une anisotropie optique pour LiBe[H.sub.3] et KBe[H.sub.3]. Via le modele de Debye quasi-harmonique qui tient compte de l'effet des phonons, nous evaluons, sur de larges bandes de pression et de temperature, la dependance en temperature du volume V(T), du module de compressibilite volumique B(T) et du coefficient d'expansion thermique α(T) et calculons les capacites calorifiques a temperature et a pression constantes [C.sub.v] et [C.sub.p], la temperature de Debye [ϴ.sub.D], l'entropie S et le parametre γ de Gruneisen. De ce cote, ces trois hydrides sont similaires. [Traduit par la Redaction] Mots-cles : structure electronique, structure cristalline, hydrides, proprietes thermodynamiques, reflectivite, coefficient d'absorption., 1. Introduction It is widely believed that within a few decades hydrogen will become the fuel that powers portable devices and most vehicles, and will become the means of storing [...]

Our calculations allowing to establish a link between atomic topology and properties, based on the interpretation of the electronic structure. ScXCo2Sb2 (X = V, Nb and Ta) double half-Heusler alloys (DHH) are nonmagnetic materials. Based on an ab initio study these materials is found to be semiconductors with an indirect band gap in the range 0.56–0.81 eV. Our DFT calculations confirm that the band gap increasing upon the replacement of V by Nb by Ta atoms. In all compounds Co-d orbitals are locating close to the Fermi level and a hybridization of Co-d, X-d and Sc-d bands lies above the Fermi level. More precisely, the optical properties have been calculated and discussed. The photon energy dependence of the dielectric function and optical conductivity is determined from 0 up to 20 eV. Prominent absorptions are observed in these compounds in the energy region of 2–4.0 eV due to interband optical transitions. The reflectivity spectra and the refraction index are also calculated and discussed. The structural stability of ScXCo2Sb2 (X = V, Nb and Ta) DHH has been confirmed by elastic constants calculations. The atomic bonds between nearest neighbors along (100) planes are weaker than those along (001) planes. However, for ScVCo2Sb2, the atomic bonds are weaker along (001). The studied materials are found to be somewhat hard compounds, elastically stable and have a brittle character except ScVCo2Sb2 compound. The positive frequencies in the phonon dispersions of ScXCo2Sb2 (X = V, Nb, Ta) DHH, indicating that they are dynamically stable. [ABSTRACT FROM AUTHOR]