A model of size-dependent Debye-Waller screening of effective potential is proposed. The calculat... more A model of size-dependent Debye-Waller screening of effective potential is proposed. The calculated effective potential of silicon nanoparticles (SiNPs) is used to predict the dependence of energy bands on diameter. The empirical pseudopotential method is implemented to calculate the band structure. SiNPs having diameters of 3.753–15.744 nm are studied. The results show that the fundamental (indirect) energy gap increases and shifts toward the center of the Brillouin zone as the diameter decreases. The direct energy gap at point Γ increases slowly as the diameter is reduced to ~5.75 nm and decreases rapidly for diameters below this value. Variations of indirect and direct energy gaps at point Γ are fitted to model equations. The results indicate a conversion to a direct energy gap when the diameter becomes ~1.6 nm. The calculated behavior of the energy gaps and the predicted transition to a direct energy gap are in good agreement with other experimental and theoretical results.
Plane waves with norm conserving pseudopotentials (PW-PP) method in conjunction with density func... more Plane waves with norm conserving pseudopotentials (PW-PP) method in conjunction with density functional theory (DFT) frame work have been used to investigate structural, electronic and optical properties of lead-halide cubic perovskite CsPbX3 (X=Br, Cl and I). The generalized gradient approximation (GGA), specifically Perdew-Burke-Ernzerhof (PBE) flavor, has been chosen to treat the exchange correlation term of Kohn-Sham equation. Structural parameters are comparable with other theoretical and experimental studies. In spite of good agreement of our band gap values with other theoretical works, however, they were not comparable when compared to the experimental values due to the well-known problem of Eg value underestimation of DFT. To update the value, we have used GW method as a self-consistent quasiparticle method on energies and wave functions and indeed they have been improved. Optical properties have been calculated using density functional perturbation theory (DFPT). Our re...
A model of size-dependent Debye-Waller screening of effective potential is proposed. The calculat... more A model of size-dependent Debye-Waller screening of effective potential is proposed. The calculated effective potential of silicon nanoparticles (SiNPs) is used to predict the dependence of energy bands on diameter. The empirical pseudopotential method is implemented to calculate the band structure. SiNPs having diameters of 3.753–15.744 nm are studied. The results show that the fundamental (indirect) energy gap increases and shifts toward the center of the Brillouin zone as the diameter decreases. The direct energy gap at point Γ increases slowly as the diameter is reduced to ~5.75 nm and decreases rapidly for diameters below this value. Variations of indirect and direct energy gaps at point Γ are fitted to model equations. The results indicate a conversion to a direct energy gap when the diameter becomes ~1.6 nm. The calculated behavior of the energy gaps and the predicted transition to a direct energy gap are in good agreement with other experimental and theoretical results.
Plane waves with norm conserving pseudopotentials (PW-PP) method in conjunction with density func... more Plane waves with norm conserving pseudopotentials (PW-PP) method in conjunction with density functional theory (DFT) frame work have been used to investigate structural, electronic and optical properties of lead-halide cubic perovskite CsPbX3 (X=Br, Cl and I). The generalized gradient approximation (GGA), specifically Perdew-Burke-Ernzerhof (PBE) flavor, has been chosen to treat the exchange correlation term of Kohn-Sham equation. Structural parameters are comparable with other theoretical and experimental studies. In spite of good agreement of our band gap values with other theoretical works, however, they were not comparable when compared to the experimental values due to the well-known problem of Eg value underestimation of DFT. To update the value, we have used GW method as a self-consistent quasiparticle method on energies and wave functions and indeed they have been improved. Optical properties have been calculated using density functional perturbation theory (DFPT). Our re...
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