This work summarizes that RbSnX3 (X = Cl, Br, I) exhibits remarkable ductility and absorption in the ultraviolet (UV) region of the electromagnetic spectrum compared to those of CsBX3 (B = Ge, Sn, Pb; X = Cl, Br, I) metal halide perovskites.

First-principles calculations are employed to investigate and compare the structural, elastic and optical properties of tantalum hemicarbide Ta 2 C and tantalum monocarbide TaC. Calculated lattice constants of these carbides are in good agreement with available theoretical and experimental results. The mechanical stability of these carbides is affirmed by the estimated values of elastic constants. The estimated values of Vickers hardness indicate that TaC is harder than Ta 2 C. The values of Pugh's ratio and Poisson's ratio suggest the brittle nature of both Ta 2 C and TaC. The optical properties of Ta 2 C along two polarization directions [001] and [100] are studied in details for the first time. Our study shows that the optical properties of both Ta 2 C and TaC compounds compliment the electronic structure calculations. Optical constants of Ta 2 C show significant dependence of the state of polarization of the incident electric field, and predict this material as optically anisotropic.and Dashora et al [19]. We would like to extend our computational work on optical properties of Ta 2 C. To the best of our knowledge till to date there is no experimental or theoretical data available on the optical properties of Ta 2 C. In this paper, we also pay attention to revisit the existing theoretical data of TaC and Ta 2 C for various physical properties (e.g. structural, elastic, electronic etc). DFT [20,21] calculations are executed on tantalum carbides Ta 2 C and TaC by using the Cambridge Serial Total Energy Package (CASTEP) code [22]. Here the electron-ion interaction is considered by ultrasoft pseudopotentials for both Ta 2 C and TaC [23]. Perdew-Burke-Ernzerhof (PBE) form of generalized gradient approximation (GGA) is used to treat the exchange correlation energy [24]. Minimization of total energy is achieved by the technique proposed by Broyden, Fletcher, Goldfrab and Shanno [25]. The optimization of crystal structure is done with a plane wave cut off energy of 850 eV and 18×18×10 Monkhorst-Pack grid [26] for Ta 2 C. In case of TaC, plane wave cut off energy of 950 eV and 19×19×19 Monkhorst-Pack grid are used for optimization. Convergence threshold of 1×10 −5 eV atom −1 for the total energy, 0.03 eV Å −1 for the maximum force, 0.05 GPa for maximum stress, and 0.001 Å for maximum displacement are taken for all calculations. Computational procedure

Hydrostatic pressure dependent structural, electronic, elastic and optical properties of Heusler compounds Cr 2 YAl (Y=Mn, Co) are investigated by the first-principles calculations. Present study shows good agreement between the calculated and experimental values of lattice parameters of these compounds. The gradual decrease of lattice parameter and unit cell volume with the increase of pressure eliminates the possibility of phase transition up to the considered pressure range 0–30 GPa. The absence of negative frequency in the phonon dispersion curves at various external pressures up to 30 GPa confirm the dynamical stability of these compounds. The values of Pugh's ratio, Poisson's ratio and Cauchy pressure indicate the ductility of Cr 2 CoAl while those criteria confirm the brittleness of Cr 2 MnAl. Pressure dependent behaviour of the elastic constants of these compounds shows the mechanical stability over the studied pressure range (0–30 GPa). Crystal stiffening of both the compounds is indicated by the increase of Debye temperature with increasing hydrostatic pressure. The pressure dependent band structure and density of states (DOS) calculations reveal the half- and the near half-metallic behaviour of Cr 2 MnAl and Cr 2 CoAl, respectively up to 20 GPa while those disappears at pressure around 30 GPa. The variations of optical constants with pressure is consistent with the results of the electronic structure calculations. High reflectivity (>45%) of both the compounds makes them attractive for optoelectronic device applications.

Structural, mechanical, spin-dependent electronic, magnetic, and optical properties of antiperovskite nitrides A 3 InN (A = Co, Ni) along with molecular orbital diagram are investigated here by using an ab initio density functional theory (DFT). The mechanical stability, deformation, damage tolerance and ductile nature of A 3 InN are confirmed from elastic calculations. Different mechanical anisotropy factors are also discussed in detail. The spin dependent electronic properties such as the band structure and density of states (DOS) of A 3 InN are studied and, the dispersion curves and DOS at Fermi level are different for up and down spins only in case of Co 3 InN. These calculations also suggest that Co 3 InN and Ni 3 InN behave as ferromagnetic and nonmagnetic, respectively. The induced total magnetic moment of Co 3 InN is found 2.735 μ B /cell in our calculation. Mulliken bond population analysis shows that the atomic bonds of A 3 InN are contributed by both ionic and covalent bonds. Molecular orbital diagrams of A 3 InN antiperovskites are proposed by analyzing orbital projected band structures. The formation of a molecular orbital energy diagram for Co 3 InN is similar to Ni 3 InN with respect to hybridization and orbital sequencing. However, the orbital positions with respect to the Fermi level ( E F ) and separations between them are different. The Fermi surface of A 3 InN is composed of multiple nonspherical electron and hole type sheets in which Co 3 InN displays a spin-dependent Fermi surface. The various ground-state optical functions such as real and imaginary parts of the dielectric constant, optical conductivity, reflectivity, refractive index, absorption coefficient, and loss function of A 3 InN are studied with implications. The reflectivity spectra reveal that A 3 InN reflects >45% of incident electromagnetic radiations in both the visible and ultraviolet region, which is an ideal feature of coating material for avoiding solar heating.

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