scholarly journals Revisiting the Zinc-Blende/Wurtzite Heterocrystalline Structure in CdS

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Zhaohui Zhou ◽  
Mingtao Li ◽  
Po Wu ◽  
Liejin Guo
Keyword(s):  
Correlation Energy ◽  
Local Density ◽  
Energy Functional ◽  
Band Alignment ◽  
Band Offset ◽  
Type I ◽  
Hybrid Functional ◽  
Generalized Gradient ◽  
Zinc Blende ◽  
Interface Location

The band offset at CdS zinc-blende (ZB)/wurtzite (WZ) heterocrystalline interface was revisited using the first principles calculations with the local density approximation (LDA), generalized gradient approximation (GGA), and Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional. It was revealed that, unlike most IV, III-V, and II-VI semiconductors, the band alignment at CdS ZB/WZ heterocrystalline interface was of type-I with straddling lineup of band edges, which was irrespective of the exchange-correlation energy functional, the thickness of ZB and WZ segments, and the ZB/WZ interface location. The partial charge densities of VBM and CBM states were separated around two adjacent interfaces in one unit cell of heterocrystalline superlattice. This type of carrier localization was mainly attributed to the spontaneous polarization occurring in the WZ segment rather than the band offset at the interface.

scholarly journals Calculation of Band Offsets of Mg(OH)2-Based Heterostructures

2021 ◽  
Vol 2 (3) ◽  
pp. 274-283
Author(s):  
Masaya Ichimura
Keyword(s):  
Solar Cells ◽  
Valence Band ◽  
Dye Sensitized Solar Cells ◽  
Band Alignment ◽  
First Principles Calculation ◽  
Band Edge ◽  
Level Energy ◽  
Type I ◽  
Valence Band Edge ◽  
Generalized Gradient

The band alignment of Mg(OH)2-based heterostructures is investigated based on first-principles calculation. (111)-MgO/(0001)-Mg(OH)2 and (0001)-wurtzite ZnO/(0001)-Mg(OH)2 heterostructures are considered. The O 2s level energy is obtained for each O atom in the heterostructure supercell, and the band edge energies are evaluated following the procedure of the core-level spectroscopy. The calculation is based on the generalized gradient approximation with the on-site Coulomb interaction parameter U considered for Zn. For MgO/Mg(OH)2, the band alignment is of type II, and the valence band edge of MgO is higher by 1.6 eV than that of Mg(OH)2. For ZnO/Mg(OH)2, the band alignment is of type I, and the valence band edge of ZnO is higher by 0.5 eV than that of Mg(OH)2. Assuming the transitivity rule, it is expected that Mg(OH)2 can be used for certain types of heterostructure solar cells and dye-sensitized solar cells to improve the performance.

Quadrupole polarizabilities and Sternheimer antishielding factors in the density functional theory

1982 ◽  
Vol 60 (2) ◽  
pp. 210-221 ◽  
Author(s):  
M. J. Stott ◽  
E. Zaremba ◽  
D. Zobin
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Correlation Energy ◽  
Local Density ◽  
Closed Shell ◽  
Energy Functional ◽  
Functional Theory ◽  
Hartree Fock ◽  
Shielding Factor ◽  
The Density Functional Theory

The quadrupole polarizability and Sternheimer antishielding factor have been calculated for selected closed-shell atoms and ions using the density functional theory. In most cases, the results agree favourably with coupled Hartree–Fock calculations. However, for atoms with valence (d-shells the local density approximation used in the calculations is found to be inadequate. Our results suggest that refinements to the exchange-correlation energy functional are required in order to obtain accurate values for the polarizability and shielding factor of (d-shell atoms within a density functional approach.

Optical Investigation of the Band Offset of CdxZn1−xTe /ZnTe and ZnSexTe1−x/ZnTe Superlattices

1990 ◽  
Vol 198 ◽  
Author(s):  
Y. Rajakarunanayake ◽  
M. C. Phillips ◽  
J. O. Mccaldin ◽  
D. H. Chow ◽  
D. A. Collins ◽  
...  
Keyword(s):  
Valence Band ◽  
Band Alignment ◽  
Band Offset ◽  
Type I ◽  
Optical Investigation ◽  
Type Ii ◽  
Carrier Injection ◽  
Valence Band Offset ◽  
Small Component ◽  
Strained Layer Superlattices

ABSTRACTWe have analyzed photoluminescence spectra from CdxZnl−xTe /ZnTe and ZnSexTel−x/ZnTe strained layer superlattices grown by MBE, and obtained the band offsets by fitting to theory. We find that the valence band offset of the CdTe/ZnTe system is quite small (-50± 160 meV). In CdxZnl−xTe /ZnTe superlattices, the electrons and heavy holes are confined in the CdxZn1−xTe layers (type I), while the light holes are confined in the ZnTe layers (type II). On the other hand, the photoluminescence data from the ZnSexTe1−x /ZnTe superlattices suggest that the band alignment is type II, with a large valence band offset (−907 ± 120 meV). We also investigated the band bowing in the ZnSexTel−x alloys by optical spectroscopy, and found that there is only a small component of bowing in the valence band, while most of the bowing occurs in the conduction band. Based on our results for band alignments, we evaluate the prospects for minority carrier injection in wide bandgap heterostructures based on ZnSe, ZnTe, and CdTe.

AB INITIO INVESTIGATION OF ELECTRONIC AND VIBRATIONAL PROPERTIES OF ZnS AND ZnSe CRYSTALS BY DIFFERENT XC-FUNCTIONALS

2009 ◽  
Vol 23 (19) ◽  
pp. 3845-3857 ◽  
Author(s):  
D. M. POPOVA ◽  
B. N. MAVRIN ◽  
A. V. SOLOV'YOV
Keyword(s):  
First Principles ◽  
Correlation Energy ◽  
Quantitative Description ◽  
Basis Set ◽  
Vibrational Properties ◽  
Hybrid Functional ◽  
Exchange Correlation ◽  
Zinc Blende ◽  
Dependent Potential ◽  
Projector Augmented Wave

Ground state properties of zinc-blende structures ZnS and ZnSe are investigated from first principles using plane wave basis, projector augmented wave method and local orbital-dependent potential, as well as a basis set of Gaussian-type functions with hybrid functionals for the approximation of exchange-correlation energy. The results of DFT calculations with the LDA, LDA+U, GGA, GGA+U, BLYP, B3P86, P3PW, BH-HP, KMLYP and B3LYP approximations are compared. It is shown that the hybrid functional B3LYP provides an accurate quantitative description of the structural, electronic and vibrational properties of ZnS and ZnSe in comparison with experimental data.

Low symmetry phases of (Al, Ga)Sb under low pressure

2015 ◽  
Vol 29 (09) ◽  
pp. 1550056 ◽  
Author(s):  
W. Tahar Belarbi ◽  
Abdelkarim Rouabhia ◽  
F. Tair ◽  
Bouhalouane Amrani ◽  
Nadir Sekkal
Keyword(s):  
Local Density ◽  
First Principle ◽  
Density Approximation ◽  
Interesting Problem ◽  
Generalized Gradient ◽  
Generalized Gradient Approximation ◽  
Zinc Blende ◽  
Lower Total Energy ◽  
Low Pressures ◽  
Low Symmetry

The interesting problem of the first phase transition which is induced by pressure in AlSb and GaSb antimonide binaries is revisited. Then, the case of the AlGaSb ternary has been investigated too. The choice of ternary AlGaSb is due to the particular attention which is given actually to it and to the quasi-absence of investigations of the phase transitions in it. We found that low pressures applied to GaSb and AlSb induce transitions from zinc-blende to Imm2 and from zinc-blende to Cmcm, respectively. Our result for AlSb is in agreement with literature, and in the case of GaSb which poses the problem, we find that the Imm2 phase presents a lower total energy than the b-β-Sn phase. For ternaries, the transition is found to be to a phase which is obtained from the Cmcm phases of binaries. Calculations were performed using the plane wave version of the FPLMTO (PLW-FPLMTO) first principle method based on the local density approximation (LDA) and the generalized gradient approximation (GGA96).

Theory of Interfaces in Wide-Gap Nitrides

1996 ◽  
Vol 449 ◽  
Author(s):  
M. Buongiorno Nardelli ◽  
K. Rapcewicz ◽  
E. L. Briggs ◽  
C. Bungaro ◽  
J. Bernholc
Keyword(s):  
Laser Diodes ◽  
Blue Laser ◽  
Band Offset ◽  
Type I ◽  
Interface Properties ◽  
Type Ii ◽  
Valence Band Offset ◽  
Bulk Properties ◽  
Conduction Band Offset ◽  
Zinc Blende

ABSTRACTThe results of theoretical studies of the bulk and interface properties of nitrides are presented. As a test the bulk properties, including phonons of GaN at the Γ-point, are calculated and found to be in excellent agreement with the experimental data. At interfaces, the strain effects on the band offsets range from 20% to 40%, depending on the substrate. The AlN/GaN/InN interfaces are all of type I, while the Al0.5Ga0.5N on A1N zinc-blende (001) interface is of type II. Further, an interface similar to those used in the recent blue laser diodes is of type I and does not have any electronically active interface states. The valence band-offset in the (0001) GaN on A1N interface is -0.57 eV and the conduction band-offset is 1.87 eV.

Synthesis and structural characterization of 3-[1-[4-(2-methylpropyl)phenyl]ethyl]-6-(4-fluorophenyl)-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole

2019 ◽  
Vol 34 (4) ◽  
pp. 325-330
Author(s):  
Gülsüm Gündoğdu ◽  
Arzu Karayel ◽  
Sevim Peri Aytaç ◽  
Birsen Tozkoparan ◽  
Filiz Betül Kaynak
Keyword(s):  
Crystal Structure ◽  
Dft Calculations ◽  
Density Functional ◽  
Correlation Energy ◽  
Local Density ◽  
Van Der Waals Interactions ◽  
Generalized Gradient ◽  
Cell Parameters ◽  
Structure Solution ◽  
The Density Functional Theory

3-[1-[4-(2-Methylpropyl)phenyl]ethyl]-6-(4-fluorophenyl)-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole (C21H21FN4S) has been synthesized as a member of a series of triazolothiadiazoles having NSAIDs moieties with cytotoxic activity. The crystal structure of this new compound has been solved and refined using conventional laboratory X-ray powder diffraction data and optimized using density functional techniques. The final structure solution was achieved by Rietveld refinement using soft restraints on all non-H atom bond lengths and angles. This compound crystallizes in $P\bar{1}\;$ space group, with the unit cell parameters a = 5.5880(4) Å, b = 9.3074(7) Å, c = 19.497(4) Å, α = 99.311(10)°, β = 91.925(9)°, γ = 98.199(6)°, and V = 988.8(2) Å3. To complement and verify the structure solution of the compound, the density functional theory (DFT) calculations were performed by using the local density approximation and the generalized gradient approximation for exchange-correlation energy. In order to see the effect of the van der Waals interactions on the electronic structure, the relevant structure was also optimized with B3LYP-D2, PBE-D2, and optB88-vdW functionals. The refined crystal structure was confirmed by the DFT calculations. The best agreement with the experimental structure was achieved by optB88-vdW functional.

scholarly journals First-Principles Study on the Stability and Electronic Structure of the Charge-Ordered Phase in α-(BEDT-TTF)2I3

Crystals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1109
Author(s):  
Takao Tsumuraya ◽  
Hitoshi Seo ◽  
Tsuyoshi Miyazaki
Keyword(s):  
Structural Optimization ◽  
First Principles ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Local Density ◽  
Ambient Pressure ◽  
Hybrid Functional ◽  
Generalized Gradient ◽  
Electronic Band ◽  
Ordered State

We theoretically study the structural and electronic properties of a molecular conductor, α-(BEDT-TTF)2I3, using first-principles density-functional theory calculations, especially in its low-temperature charge-ordered state at ambient pressure. We apply a hybrid functional approach and compare the results with a conventional exchange-correlation functional within the generalized gradient approximation. By performing structural optimization, we found a stable charge-ordered solution for the former, in contrast to the latter approach where the magnitude of the charge imbalance becomes considerably small compared to that when the experimental structure is adopted. The electronic band structure near the Fermi level, with and without structural optimization, as well as the molecule-dependent local density of states of the charge-ordered state are discussed.

scholarly journals Making EuO multiferroic by epitaxial strain engineering

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Veronica Goian ◽  
Rainer Held ◽  
Eric Bousquet ◽  
Yakun Yuan ◽  
Alexander Melville ◽  
...  
Keyword(s):  
Phase Transition ◽  
Ferroelectric Phase Transition ◽  
Density Functional ◽  
Tensile Strain ◽  
Ferroelectric Phase ◽  
Local Density ◽  
Weak Ferromagnetism ◽  
Strain Engineering ◽  
Hybrid Functional ◽  
Generalized Gradient

Abstract Multiferroics are materials exhibiting the coexistence of ferroelectricity and ideally ferromagnetism. Unfortunately, most known magnetoelectric multiferroics combine ferroelectricity with antiferromagnetism or with weak ferromagnetism. Here, following previous theoretical predictions, we provide clear experimental indications that ferroelectricity can be induced by epitaxial tensile strain in the ferromagnetic simple binary oxide EuO. We investigate the ferroelectric phase transition using infrared reflectance spectroscopy, finding that the frequency of the soft optical phonon reduces with increasing tensile strain and decreasing temperature. We observe such a soft mode anomaly at 100 K in (EuO)2/(BaO)2 superlattices grown epitaxially on (LaAlO3)0.29-(SrAl1/2Ta1/2O3)0.71 substrates, which is a typical signature for a displacive ferroelectric phase transition. The EuO in this superlattice is nominally subjected to 6.4% biaxial tensile strain, i.e., 50% more than believed needed from previously published calculations. We interpret our results with new first-principles density functional calculations using a hybrid functional, which provides a better quantitative agreement with experiment than the previously used local-density approximation and generalized gradient approximation functionals.

scholarly journals COMPARISON OF DENSITY FUNCTIONAL APPROXIMATIONS IN THE JELLIUM MODEL FOR METAL CLUSTERS

2001 ◽  
Vol 15 (10n11) ◽  
pp. 1724-1727 ◽  
Author(s):  
CARLOS FIOLHAIS ◽  
L. M. ALMEIDA
Keyword(s):  
Monte Carlo ◽  
Density Functional ◽  
Alkali Metals ◽  
Correlation Energy ◽  
Local Density ◽  
Jellium Model ◽  
Generalized Gradient ◽  
Exchange Correlation ◽  
Generalized Gradient Approximation ◽  
Exchange And Correlation

We calculated the exchange, correlation and total energies of clusters of alkali metals with N=1-150 atoms in the spherical jellium model. The calculations were made using the Kohn-Sham method with exchange and correlation energies evaluated in the meta-generalized gradient approximation (MGGA), proposed by J. P. Perdew, S. Kurth, A. Zupan and P. Blaha, in the generalized gradient approximation (GGA) of J. P. Perdew, K. Burke and M. Ernzerhof, and in the Local Density Approximation (LDA). We evaluated the relative deviations of MGGA and GGA energies with respect to LDA. Exchange energies of MGGA and GGA are more negative than the LDA exchange energy and become closer to this as the cluster size increases. On the other hand, the GGA and MGGA correlation energies, which are almost identical, are less negative than LDA. The deviations of GGA and MGGA exchange-correlation energies with respect to LDA are smaller than those of the exchange and correlation energies separately. For clusters with 18 and 20 atoms we have compared our jellium results with Variational and Diffusion Monte-Carlo results. Errors of LDA for exchange and correlation tend to cancel so that the total exchange-correlation energy is close to the Monte-Carlo results. Similar cancellations occur with GGA and MGGA. We also examined the validity of the liquid drop model.

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