Modulation of optical absorption in m-Fe1−xRuxS2 and exploring stability in new m-RuS2

Abstract

A first-principle computational method has been used to investigate the effects of Ru dopants on the electronic and optical absorption properties of marcasite FeS2. In addition, we have also revealed a new marcasite phase in RuS2, unlike most studied pyrite structures. The new phase has fulfilled all the necessary criteria of structural stability and its practical existence. The transition pressure of 8 GPa drives the structural change from pyrite to orthorhombic phase in RuS2. From the thermodynamical calculation, we have reported the stability of new-phase under various ranges of applied pressure and temperature. Further, from the results of phonon dispersion calculated at Zero Point Energy, pyrite structure exhibits ground state stability and the marcasite phase has all modes of frequencies positive. The newly proposed phase is a semiconductor with a band gap comparable to its pyrite counterpart but vary in optical absorption by around 106 cm−1. The various Ru doped structures have also shown similar optical absorption spectra in the same order of magnitude. We have used crystal field theory to explain high optical absorption which is due to the involvement of different electronic states in formation of electronic and optical band gaps. Lӧwdin charge analysis is used over the customarily Mulliken charges to predict 89% of covalence in the compound. Our results indicate the importance of new phase to enhance the efficiency of photovoltaic materials for practical applications.

Pressure-Induced Enhanced Optical Absorption in Sulvanite Compound Cu3TaX4 (X = S, Se, and Te): An ab Initio Study

“…The real part ε 1 (ω) is derived from ε 2 (ω), employing the Kramer–Kronig equation. All other optical constants follow from the dielectric functions using standard equations. , The intraband transition contribution to the dielectric functions are inconspicuous, given the semiconducting nature of the compounds, and also the indirect interband transitions are neglected with comparison to direct interband transition, considering low photon momentum. The plot of the real part of the dielectric function with respect to the incident photon energy, at 0 and 10 GPa pressure, is shown in Figure (a),(b),(c).…”

“…The ground states were determined with calculations performed within Perdew–Burke–Ernzerhof’s generalized gradient approximation (GGA) . The underestimation of the band gap magnitude with PBE is a well-known issue − and is documented in almost every ab initio based report. This happens because band gap is expressed as the difference in eigenvalues of the conduction band minimum (CBM) and the valence band maximum (VBM).…”

“…All other optical constants follow from the dielectric functions using standard equations. 29,39 The intraband transition contribution to the dielectric functions are inconspicuous, given the semiconducting nature of the compounds, and also the indirect interband transitions are neglected with comparison to direct interband transition, considering low photon momentum. The plot of the real part of the dielectric function with respect to the incident photon energy, at 0 and 10 GPa pressure, is shown in Figure 6 The optical conductivity plots shown in Figure 7(a)−(c) show a forbidden conduction region with energies corresponding to higher infrared and lower visible spectra, which further reconfirms the semiconducting nature of the compound.…”

Engineering of Hydrogenated (6,0) Single-Walled Carbon Nanotube under Applied Uniaxial Stress: A DFT-1/2 and Molecular Dynamics Study

“…The real part ϵ 1 (ω) characterizes the degree of polarization under an external electric field, and the imaginary part ϵ 2 (ω) characterizes the interband electronic transition from occupied states to unoccupied states. 87,88 ϵ 2 (ω) can be directly calculated from the one-electron orbitals and energies obtained from the Kohn−Sham equations. It is given by the equation below 89,90 ) where p is the momentum operator, k n | > is the eigenfunction of the eigenvalue, and f k ( ) n is the Fermi Distribution function.…”

Monoclinic–triclinic phase transition induced by pressure in fergusonite-type YbNbO4

“…Additional support to the previous hypothesis comes from DFT calculations. Usually the enthalpy versus pressure curve provide a clear picture of pressure-driven phase transitions [39,40]. However, in the case of second-order phase transitions (like fergusonite-scheelite) and gradual transitions (like fergusonite-triclinic)-as those involved in this work-enthalpy calculations cannot always discriminate between the involved structures because the small differences in calculated enthalpies are below the simulation precision [8,41].…”