Navegando por Autor "Moreira, E."
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Artigo 3R and 2H polytypes of MoS2: DFT and DFPT calculations of structural, optoelectronic, vibrational and thermodynamic properties(Elsevier, 2017-12) Coutinho, S.S.; Barboza, Carlos Antonio; Tavares, M.S.; Frazão, N.F.; Moreira, E.; Azevedo, David L.We report the results of a theoretical study on the behavior of the structural, optoelectronic, vibrational, including infrared and Raman theoretical spectra, phonon spectrum, and thermodynamic properties of 3R- and 2H- polytypes of molybdenum disulfide (MoS2) using density functional theory (DFT) considering both the local density and generalized gradient approximation, LDA and GGA, respectively. Calculated lattice parameters are close to the experimental measurements, and an indirect band gap E(A→KΓ)¼ 1:33 eV (0.68 eV) was obtained within the GGA (LDA) level of calculation, considering the 3R-polytype, and for the 2H- polytype an indirect band gap E(Γ→KΓ)¼ 1:30 eV (0.70 eV) was obtained within the GGA (LDA) approximation. The complex dielectric function and absorption of 3R-MoS2 and 2H-MoS2 polytypes were shown to be sensitive to the plane of polarization of the incident light. The phonon dispersion relation together with density of states (DOS) as well as theoretical peaks of the infrared (IR) and Raman spectra in the frequency range of 0–800 cm 1 was analyzed and assigned, considering the norm-conserved pseudopotentials. The thermodynamic potentials, the specific heat at constant volume and Debye temperature of the 3R-MoS2 and 2H-MoS2 polytypes are also calculated, whose dependence on the temperature are discussed.Artigo Structural, optoelectronic, infrared and Raman spectra from first principles calculations of γ-Cd(OH)2(Elsevier, 2015-01) Barboza, Carlos Antonio; Henriques, J.M.; Albuquerque, E.L.; Fulco, U.L.; Moreira, E.Wehaveinvestigatedthephysicalpropertiesofthecadmiumhydroxidepolymorph γ-Cd(OH)2 using density-functional theory(DFT)consideringboththelocaldensityandgeneralizedgradientapproxima- tions, LDAandGGA,respectively.Theelectronicbandstructure,theelectronicdensityofstates,the dielectric functionandtheopticalabsorptionarecalculated.Acomparisonrevealsgoodagreementof the calculatedlatticeparameterswithexperimentalresults.Adirectbandgap EðΓ-ΓÞ ¼ 1:70 eV (1.53eV)wasobtainedwithintheGGA(LDA)levelofcalculation.Thevibrationalnormalmodesaswell as the Raman and infrared spectraof γ-Cd(OH)2 were obtained and assigned.Artigo Vibrational and thermodynamic properties of orthorhombic CaSnO3 from DFT and DFPT calculations(Elsevier, 2015-02) Barboza, Carlos Antonio; Moreira, E.; Albuquerque, E.L.; Fulco, U.L.; Henriques, J.M.; Araújo, A.I.Density functional theory (DFT) and density functional perturbation theory (DFPT) calculations were used to investigate the vibrational and thermodynamic properties of orthorhombic stannate CaSnO3 compound. Our approach was based on the generalized gradient approximation with dispersion correction (GGA+D), considering the norm-conserved pseudopotentials. The phonon dispersion relation as well as theoretical peaks of the infrared (IR) and Raman spectrum in the frequency range of 100–800 cm−1 was analyzed and assigned. The thermodynamic potentials and the specific heat at constant volume of the CaSnO3 compound are also calculated, whose dependence with the temperature are discussed.