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The present work aims at investigating the electronic, optical, photovoltaic and thermoelectric properties of AgBiS2 compound using the density functional theory (DFT) and the modified Becke-Johnson exchange-correlation potential (mBJ). Both hexagonal Matildite and cubic Schapbachite polymorphs were considered. The hexagonal phase is found to be indirect gap semiconductor with band gap energy of about 1.07 eV and high absorption coefficient of 106 cm−1, whereas the cubic phase were metallic. The analysis of band alignment of Matildite with some binary oxides and sulfides revealed interesting results. The photovoltaic properties of AgBiS2 confirmed that Matildite phase could achieve a short-circuit current of 22 mA/cm2 and conversion efficiency of 20%. Also, we demonstrated that including photon recycling with a proper solar cell design could improve the conversion efficiency. Moreover, interesting thermoelectric performance has been confirmed.

In this study, first-principles investigations were performed using the full-potential linearized augmented plane-wave method of the structural and optoelectronic properties of thorium germinate (ThGeO4), a high-K dielectric material. Under ambient conditions, the structural properties calculated for ThGeO4 in the zircon phase were in excellent agreement with the available experimental data. Furthermore, using the modified Becke -Johnson correction method, the calculated band gaps and optical constants accurately described this compound. Finally, the thermal properties were predicted over a temperature range of 0–700 K and pressures up to 11 GPa using the quasi-harmonic Debye model, where the variations in the heat capacity, primitive cell volume, and thermal expansion coefficients were determined successfully.

First principles calculations were carried out on the SrMoO4 compound which has been of interest owing to its technologically important physical properties. The structural, electronic, optical and thermal properties of this compound have been investigated under low pressure (LP) through the full potential linearized augmented plane wave method (FP-LAPW) within the framework of density functional theory. It is found that the phase transition from zircon to scheelite type structure occurs at negative pressure. The calculated ground state properties in scheelite structure are found to be in good accord with previously published data. Using the recently developed Tran Blaha-modified Becke Johnson approach, we have also studied the electronic band structure of this compound which shows the semiconducting behavior with a direct band gap of 4.30 eV in the scheelite phase, whereas the band gap is found to be 2.18 eV in the zircon phase. Various thermodynamic properties including the thermal volume expansion coefficient and heat capacities at constant volumes and pressures were calculated via the quasi-harmonic Debye model at different temperatures (0–1000 K). Furthermore, optical properties such as complex dielectric function, refractive index, and reflectivity spectra of the titled compound were studied for incident electromagnetic waves in an energy range up to 16 eV. The contributions to various transitions peaks in the optical spectra are analyzed and discussed with the help from the energy dependent imaginary part of the dielectric function.

The optical absorbance of four ternary thin films, i.e. MgSiP2, MgGeP2, MgSiAs2, MgGeAs2 have been theoretically examined over a wide range of wavelength from 300 nm to 800 nm. The combination of first-principle electronic structure calculations and the optical matrix approach for modeling the multilayer assembly have been employed for theoretical studies. The analysis of the calculated absorbance spectra at room temperature with unpolarized light and normal incidence, revealed that MgGeAs2 with a direct energy band gap of 1.6 eV exhibit a considerable high optical absorption, where a thickness of 3.2 μm of this thin film is sufficient to absorb 90% of the incident light and generates a maximum photocurrent of ∼23 mA/cm2.

A first principles study of structural, electronic and optical properties of zinc aluminum oxide (ZnAl 2 O 4 ) by means of the full potential linear augmented plane wave method is presented. The local density approximation is used for the exchange-correlation potential. A direct band gap of 4.19 eV, in agreement with experiment ( E g =3.9 eV), was determined. ZnAl 2 O 4 is transparent in the visible spectral region; the excitonic transition associated with the fundamental band gap is 4.17 eV. The refractive index value is 1.74 in the ultraviolet spectral region.

Refractive indices and birefringences for some representative uni-axial crystals such as II- SiP 2 and II- GeP 2 have been determined over a wide range of wavelengths by the use of first-principles electronic structure calculations. First, the calculated refractive indices are fitted usually by a generalized Sellmeier equation which consists of several oscillation terms involve in its parameters more direct information about material such as electronic transitions or resonance wavelengths. Then, in contrast to all other semiconductors under discussion our spectra show a negative birefringence for CdSiP 2 in agreement with the experimental data, and they exhibit a considerable dispersion near the band gap.

In order to get a good overall description of the structural, electronic and optical properties of ternary chalcopyrite semiconductors especially for ZnSiAs2 and CdSiAs2, they have been calculated self consistently using the full potential augmented plane wave plus local orbital method (FPAPW+lo). The calculations are presented within the local density approximation (LDA), where we clarify the electronic and optical properties for both compounds. Since, we prove the existence of the direct band gap and also the efficiency of the method to give more details about the optical properties. We found that the most important features of the band gap is pseudo-direct for ZnSiAs2, and direct for CdSiAs2; then the contribution of the different transitions peaks are analyzed from the imaginary part of the dielectric function and the reflectivity spectra.

Full Potential Augmented Plane Wave plus local orbital method ( FAPW+lo) calculations were performed for ZnSiP2, ZnGeP2, and ZnSnP2 in the chalcopyrite structure in order to investigate the optical properties and to show the origin of the different optical transitions and their correspondence in the band structure. It is found that the most important features of the band gap is pseudo-direct for ZnSiP2, indirect for ZnGeP2, and direct for ZnSnP2. Then the contribution of the different transitions peaks are analyzed from the imaginary part of the dielectric function and the reflectivity spectra.

We investigated the pressure dependence of the excitation energies of the ternary CdXP2 (with X=Si, Ge and Sn) pnictide semiconductors in the chalcopyrite structure. Using a new full potential augmented plane wave plus local orbitals method, we have studied the effect of high pressure on the band structure and on the optical properties. We show that the pseudodirect band gap of CdSiP2 narrows with increasing pressure and the direct band gap of CdGeP2 changes to a pseudo-direct band gap. Furthermore, we find that the magnitude of the pressure coefficients for this series of materials changes from the pseudodirect to a direct band gap.

The optical properties of a ternary CdSnP 2 semiconductor have been studied in the chalcopyrite structure using the full potential augmented plane wave plus local orbital method (FPAPW + lo ). First, we present the main features of the structural and electronic properties of this compound, where the electronic band structure shows that the fundamental energy gap is direct at the centre of the Brillouin zone. The contribution of the different bands were analysed from the total and partial density of states curves. Moreover, our calculated optical properties suggest that there is an anisotropic optical conductivity of this crystal along both principal directions E ⊥ c axis and E ∥ c axis. The different direct interband transitions have been determined from the imaginary part of the dielectric function.

Equilibrium lattice constants, bulk modulus, electronic band structure, and different optical transitions calculated by means of the full potential linearized augmented plane wave method are presented for BeCN2 in the chalcopyrite structure. Analysis of the band structure suggests a pseudo-direct band gap, which refers to an indirect band gap in binary compounds. We also discuss the relationships of the principal band gaps of the c-BN zinc-blende analogs. We investigate the assignment of the different optical transitions that are discussed in more detail from the reflectivity spectra. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)