Hybrid DFT calculations of the band structure of alpha-Sn (original) (raw)
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Ab initio calculation of electronic and optical properties of metallic tin
Journal of Physics Condensed Matter, 2009
The electronic and optical properties of the metallic bcc and β-Sn phases of tin are studied using density functional theory. The effects of spin-orbit coupling are examined and significant splittings are found in the band structures for both phases. Based on ab initio band structures we calculate the anisotropic optical response of β-Sn. Both intra-and interband contributions are included and the plasma frequencies for both the ordinary and extraordinary optical axis are calculated. The theoretical results are found to be in excellent agreement with experimental spectra for the anisotropic optical response. We identify the electronic transitions responsible for the dominant interband resonances in the near-infrared response.
Tight-binding description of the electronic structure and total energy of tin
Philosophical Magazine Part B, 2002
The Naval Research Laboratory (NRL) tight-binding (TB) method was applied to tin, a material which is known to exist in the diamond structure (¬-Sn) at zero temperature and low pressures. A small change in the pressure drives tin to the-Sn structure, which is stable up to 9.5 GPa at room temperature. In this paper we present the NRL-TB parameterization for tin, applying it to the study of the bulk properties of both ¬-Sn and-Sn. The parameters were determined by ®tting to a database of ®rst-principles band structures and total energies, generated using the general potential linearized augmented plane-wave method for the fcc, bcc, sc and diamond structures, with limited information from calculations of the-Sn phase. We report the success of this method in predicting the two stable structures ¬-Sn and-Sn in the correct order, even though these structures have a small energy di erence. We also discuss the NRL-TB method's ability to calculate electronic band structures and density of states. We con®rm the semimetallic and metallic character for the ¬-Sn and bcc phases respectively. We also calculate the elastic constants of ¬-Sn and-Sn, as well as several highsymmetry point phonon frequencies of ¬-Sn and compare our results with experiment. Finally, TB molecular dynamics calculations are used to explore the behaviour of tin at ®nite temperatures. We compute the temperature dependence of the Debye±Waller B factor, ®nding it to be consistent with experiment up to room temperature.
Physical Review Materials, 2020
The effects of Sn 5s lone pairs in the different phases of Sn sulphides are investigated with photoreflectance, hard x-ray photoemission spectroscopy (HAXPES) and density functional theory. Due to the photon energy-dependence of the photoionisation cross-sections, at high photon energy, the Sn 5s orbital photoemission has increased intensity relative to that from other orbitals. This enables the Sn 5s state contribution at the top of the valence band in the different Sn-sulphides, SnS, Sn 2 S 3 , and SnS 2 , to be clearly identified. SnS and Sn 2 S 3 contain Sn(II) cations and the corresponding Sn 5s lone pairs are at the valence band maximum (VBM), leading to ∼1.0-1.3 eV band gaps and relatively high VBM on an absolute energy scale. In contrast, SnS 2 only contains Sn(IV) cations, no filled lone pairs and therefore has a ∼2.3 eV room temperature band gap and much lower VBM compared with SnS and Sn 2 S 3. The direct band gaps of these materials at 20 K are found using photoreflectance to be 1.36, 1.08 and 2.47 eV for SnS, Sn2S3 and SnS2, respectively, which further highlights the effect of having the lone pair states at the VBM. As well as elucidating the role of the Sn 5s lone pairs in determining the band gaps and band alignments of the family of Sn-sulphide compounds, this also highlights how HAXPES is an ideal method for probing the lone pair contribution to the density of states of the emerging class of materials with ns 2 configuration.
First-principles study of SnS electronic properties using LDA, PBE and HSE06 functionals
Philosophical Magazine, 2017
In recent years, tin sulfide (SnS) has emerged as a promising alternative to conventional CIGS and CZTC solar cells because of the suitable electronic properties. Despite the rapid development of SnS in solar cells application, the performance of the devices based on is still low. One of the reasons is poorly understood properties of the material. The goal of this work the is a study of electronic structure using theoretical approaches. We studied the electronic properties of SnS using several exchange-correlation functionals such as LDA, PBE, and HSE06. The large variation of bandgap appears in previous theoretical reports as well as in this work. We have supposed that the variation is related to an appeared excessive hydrostatic pressure due to using not sufficiently relaxed lattice parameters. The analysis shows that HSE06 functional has the best match with experimentally obtained valence band spectra from XPS measurements. However, besides underestimation of bandgap, LDA shows the satisfactory agreement with valence band XPS spectrum .
Existence of the β-tin structure in Sr: First evidence from computational approach
Molecular Dynamics (MD) calculation is one of the most powerful theoretical methods widely used to predict and to confirm structural phase transitions. In this work, the MD method has been used to verify phase transition from body-centered cubic (bcc) to β-tin structure, then, to the Cmcm and hexagonal close-packed (hcp) structure, respectively. The transition sequence from previous theoretical works has been confirmed. In this study, Density Functional Theory (DFT), has been used to calculate phonon dispersion to confirm the stability of β-tin and hcp phases. The long time discrepancies in transition sequence between the calculation and the experimental works has been explained by conventional DFT calculation using screened exchange local density approximation (sX-LDA). More importantly, the existence of β-tin structure is finally predicted and the transition nature of Sr has also been revealed.
Spectroscopic properties of few-layer tin chalcogenides
Journal of Physics: Materials, 2019
Stable structures of layered SnS and SnSe and their associated electronic and vibrational spectra are predicted using first-principles DFT calculations. The calculations show that both materials undergo a phase transformation upon thinning whereby the in-plane lattice parameters ratio a/b converges towards 1, similar to the high-temperature behaviour observed for their bulk counterparts. The electronic properties of layered SnS and SnSe evolve to an almost symmetric dispersion whilst the gap changes from indirect to direct. Characteristic signatures in the phonon dispersion curves and surface phonon states where only atoms belonging to surface layers vibrate should be observable experimentally.
Optical properties of monoclinic SnI2 from relativistic first-principles theory
Physical Review B, 1997
Within the local-density approximation, using the relativistic full-potential linear muffin-tin orbital method, the electronic structure is calculated for the anisotropic, layered material SnI 2 . The direct interband transitions are calculated using the full electric-dipole matrix elements between the Kohn-Sham eigenvalues in the ground state of the system. The inclusion of spin-orbit coupling was found to change the optical properties of this material considerably. Polarized absorption and reflection spectra are calculated and compared with recent experimental results. The experimentally suggested cationic excitation for the lowest-energy transition is confirmed. From the site and angular momentum decomposed electronic structure studies and the detailed analysis of the optical spectra it is found that the lowest-energy transition is taking place between Sn 5s ͑atom type 2a͒ → Sn 5p ͑atom type 4i͒ states. The ground state calculation was repeated using the tight-binding linear muffin-tin orbital-atomic sphere approximation method, and the resulting band structure agrees very well with the one calculated with the full-potential method. In contrast to recent experimental expectations, our calculations show an indirect band gap, which is in agreement with earlier semiempirical tight-binding calculations as well as with absorption and reflection spectra.
Energy –Band Structure and Optical Properties of SnS Compound
Abstract— In this paper, based on first-principles calculations within the pseudopotential theory calculated the band states of crystals SnS with rhombic lattice structure. According to the calculated band structure of the compound SnS valence band can be divided into three subgroups. Analysis of wave functions of valence states shows that the lowermost group separated from the main group of valence band by a wide energy gap about 6eV, arises from s – states of anion. The next group, consisting of four bands and located near-7eV is due to s-states of Sn. The uppermost group of twelve bands located in the range between 0 and – 5eV appears p-states of cation and anion. Analysis of origin valence states is suitable with photoelectron emission data. The width of forbidden zone computed using energy-band structure is suitable to its experimentally determined value. Spectral dependence of refraction index, reflection coefficient, of the real and imaginary parts of optical electric conduction, of the characteristic function of electron energy losses and the effective state density of compound for e||c and e^c polarizations have been done.