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Functionalized MXenes have attracted great interest due to their unique electrical, magnetic, optical, and electrochemical properties. In this paper, the effect of interlayer coupling on the electronic structures of Ti 2 CO 2 MXenes is investigated by using density functional theory. Due to the interlayer coupling, the band structures of Ti 2 CO 2 nanosheet are split, generating an indirect band gap of 0.869 eV, which is smaller than that of Ti 2 CO 2 monolayer (1.044 eV). Biaxial strain can be used to achieve the transitions of direct-indirect-negative band gaps semiconductor. The interlayer interaction effectively inhibits the structural changes under stress, resulting that the band gap of nanosheet be adjusted in a large stress range. Furthermore, the change trend of imaginary part ε 2 of the dielectric function indicates that stress has an obvious regulatory effect on the optical transition. The different responses of monolayer and nanosheet under stress provides more choice for the optical devices of Ti 2 CO 2 MXenes. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the electronic and optical properties of MgO nanosheet in (100) and (111) directions. Our calculations carried out under the framework of density functional theory (DFT) exploiting WIEN2K code with Full potential, periodic boundary conditions, augmented plane-wave basis sets and GGA approximation. Electronic results indicate that MgO(111) nanosheet has an indirect band gap of 3.67 eV and MgO(100) nanosheet has a direct band gap of 3.14 eV. MgO(100) nanosheet exhibit more ionic bonding than MgO(111) and MgO(111) has more covalent bonding than MgO(100) nanosheet. Moreover, the optical results indicate that variation of dielectric function in x direction is more than the z direction. DOS and imaginary part of the dielectric function survey confirm semiconductor properties with different bang gap for structures. Comparing the imaginary part of dielectric functions in x and z directions for two structures, blue and red shift have been observed respectively. Our results indicate that these two nanostructures are transparent in a wide range of energy spectra and have low reflectivity. [ABSTRACT FROM AUTHOR]

The ultrasoft pseudopotential planewave (UPPW) within density functional theory (DFT) has been used to investigate the electronic structure, optical, elastic and thermodynamics properties of newly binary boron nitride (T-B 3 N 3 ). The calculated lattice parameters are in good agreement with previous theoretical results and deviated are less than 0.4%. The electronic structure showed that the T-B 3 N 3 is metallic, and the optical spectra exhibit a noticeable anisotropy. The static dielectric constants, optical permittivity constants and the elastic properties are calculated. From our results, we observe that T-B 3 N 3 is mechanically unstable and ductile. The entropy, enthalpy, free energy, heat capacity and Debye temperature of T-B 3 N 3 was obtained. Up to now, there are no available experimental data about those properties. The results obtained in the present paper could provide important reference data for future studies. [ABSTRACT FROM AUTHOR]

Abstract: In this paper some structural, electronic and optical properties of BaF2 scintillator crystal have been calculated in cubic phase. Calculations were performed in DFT framework using FP-LAPW method and GGA and GGA+U approximations for exchange-correlation potential. In structural calculation part, optimum lattice constant and bulk modulus were calculated and these quantities are in good agreement with experimental and theoretical values. In electronic calculation part, energy band structure has been obtained along high symmetry points in k-space. Electronic and optical results with calculated energy gap by a semi-empirical method show that obtained energy gap of both GGA and GGA+U approximations is in good agreement with experimental values and band gap increases with increasing pressure. Also, in this work some optical properties of BaF2 compound such as dielectric function, energy loss function, optical conductivity and refractive index have been obtained. The peaks of optical conductivity are in good agreement with experimental results from reflectance spectroscopy of BaF2 compound. The obtained refractive index is in very good agreement with experimental values in the wavelength range 0.15–2.3μm. [Copyright &y& Elsevier]

Abstract: BC5 is a newly synthesized superhard material. We present a systematic investigation of optical properties of BC5 in P3m1 and I-4m2 phases at ambient and high pressure in the framework of density functional theory with the generalized gradient approximation (GGA) in this paper. Optical properties such as dielectric function, refractive index, absorption, reflectivity and electron energy-loss spectrum are obtained successfully. The feature in the spectra of the optical parameters is discussed. Through calculation, we find BC5 is optically anisotropic. Moreover, the dielectric function exhibits a large change at 70GPa pressure for P3m1 BC5 phase, but I-4m2 phase not, indicating the stable electronic structure that the I-4m2 phase possesses. [Copyright &y& Elsevier]