Spin-polarized Density Of States Research Articles

Theoretical investigations of structural, electronic, magnetic, and optical properties of group V (X = V, Nb, Ta) added CeO2-X materials for optoelectronic applications.

Depletion of natural resources, responsible for energy production, is a serious concern for researchers to develop alternate energy resources or materials. Scientists have proposed various energy materials which are based on semiconductors and their underlying physics. Cerium oxide (CeO2) is a versatile energy material which receives much attention owing to excellent photocatalytic, photonic, thermal stability, and optoelectronic applications. Even though CeO2 exhibited remarkable physical properties, but yet, they can be enhanced upon suitable doping. Focus on current research is to dope group V elements into CeO2 in order to enhance its electronic and optical response. The density of states (DOS) and band gaps of proposed materials are calculated, and significant improvement is noted after applying TB-mbj method. Optical absorption spectra of V/Nb/Ta-doped CeO2 show blueshift and decrease in reflectivity along with the presence of magnetism illustrate potential uses of these materials in future UV optoelectronics, spintronics, sensing, and energy harvesting devices. This research is based on computational work carried using Wien2k code where PBE-GGA approximation is used to approximate exchange and correlation potentials. Supercells of vanadium/niobium/tantalum-doped CeO2 are constructed, and spin-polarized density of states (DOS) along with optical constant are calculated. TB-mbj method is used to bring improvements in DOS and band gaps of proposed materials. Iterations are conducted using convergence criterion, and non-relativistic calculations are performed.

Spin-polarized electrical transport properties of organic radicals in presence of zigzag-graphene nanoribbon leads.

The present work delves into the spin-polarized transport property of organic radicals sandwiched between two zigzag-graphene nanoribbon (ZGNR) electrodes by employing density functional theory and nonequilibrium Green's function technique. We demonstrated that the magnetic center(s) of the radical can manipulate the localized edge states of the ZGNR in the scattering region, causing ferromagnetic coupling. Such manipulation of the magnetic edges results in a high spin-filter effect in molecular junctions, and even the antiferromagnetic diradicals serve as nearly perfect spin filters. We have confirmed that this is a general phenomenon of ZGNR by analyzing two antiferromagnetic diradicals and a doublet. The spin-polarized density of states, transmission spectra, and current vs voltage curves of the systems provide strong evidence for our findings. This research strongly suggests that ZGNRs attached with organic radicals could be the perfect building blocks for spintronic materials.

Interfacial negative magnetization in Ni encapsulated layer-tunable nested MoS2 nanostructure with robust memory applications.

Combining interfacial interactions and layer-number tunability, the evolution of magnetism in low-dimensional diamagnetic systems like MoS2 is indeed an interesting area of research. To explore this, Ni nanophases with an average size of 12 nm were encapsulated in MoS2 and the magnetization dynamics were studied over the temperature range of 2-300 K. Surprisingly, the newly formed hybrid nanostructure was found to have a negative magnetization state with giant exchange bias that showed a reversible temperature-induced increase in both spin magnetic moment and coercivity. Density functional theory calculations proved an interfacial charge transfer interaction with a spin-polarized density of states. The magnetization state, along with giant exchange correlation among the magnetic clusters, suggested the possibility of robust thermomagnetic memory. The dc magnetization and relaxation, investigated with different measurement protocols, unveiled robust thermoremanent magnetization as a memory effect. The time-dependent magnetization study indicated that contributions from the negative magnetization state along with charge transfer induced spin states are responsible for the memory effect, which can be controlled by both temperature and external field.

Efficient detection of specific volatile organic compounds associated with COVID-19 using CrX2 (X = Se, Te) monolayers

Motivated by the necessity of efficient detection of COVID-19 through specific biomarkers, such as ethyl butyrate and heptanal, we performed first principles calculations based on density functional theory (DFT) to explore the sensing mechanism of pure, vacancy-induced, and single atom catalyzed CrX2 (X = Se, Te) monolayers. Both the biomarkers barely bind on pristine CrSe2. However with Se-vacancy (As-doping) suitable adsorption energies of −1.44 (−0.70), and −0.70 (−0.54) eV were obtained for ethyl butyrate and heptanal, respectively. Te-vacancy (Sn-doping) in CrTe2 resulted in much stronger binding of ethyl butyrate and heptanal with the adsorption energies of −2.04 (−2.40), and −2.90 (−2.40) eV, respectively. The adsorption of the mentioned biomarkers altered the magnetic and electronic properties of defected CrX2, which were explored through spin-polarized density of states, electrostatic potential and work function calculations. Measurable changes in electronic and magnetic properties confirmed excellent sensing potential of CrX2. Statistical thermodynamics analysis based on Langmuir adsorption model was employed to study the sensing of the biomarkers at different temperature and pressure ranges for real-world application.

Influence of main-group elements on structural, electronic, magnetic and half-metallic properties of DO3-type Mn3Z (Z = Al, Ga, In, Si, Ge, Sn, P, As and Sb) alloys - A DFT study

We investigate the influence of main-group elements belonging to group III (Al, Ga and In), IV (Si, Ge and Sn) and V (P, As and Sb) on structural, electronic, magnetic and half-metallic (HM) properties of DO3-type Mn3Z alloys using density functional theory (DFT). In particular, we emphasize on the correlation between structural parameters (lattice constant) and the changes in electronic and magnetic properties of Mn3Z alloys. From full geometry optimization results, we find that the entire Mn3Z alloys stabilized to ferrimagnetic ordering. Further, the spin-polarized density of states (DOS) calculation reveals that Mn3Z (Z = Al, Si, Ge, Sn, As and Sb), Mn3Ga and Mn3In alloys exhibit, respectively, half-metallic (HM), nearly half-metallic (NHM) and metallic nature. While, the Mn3P alloy displays spin-gapless semiconducting (SGS) feature, in which spin-up and spin-down channels show metallic and spin-gapless feature, respectively. The Mn3Al, Mn3Z (Z = Si, Ge and Sn) and Mn3Z (Z = P, As and Sb) alloys follow Slater-Pauling rule well, and gives 100 % spin-polarization at the Fermi energy (EF) with total integer magnetic moment of 0, 1 and 2 μB/f.u, respectively. The contribution to total magnetic moment in all the Mn3Z alloys comes predominantly from Mn(Y) atoms. The molecular orbital (MO) hybridization mechanism is proposed to rationalize the HM band gap.

Analysis of Structural Stability and Half-Metallic Ferromagnetism of Cs2VX6 (X=Cl, Br) Double-Perovskites for Spintronic Applications: Ab-Initio Simulations

Spintronics has become an emerging field based on electronic spin usage for various technological applications. Herein, we explored the ferromagnetic characteristics of novel double-perovskite Cs2VX6 (X=Cl, Br) compounds within the framework of density functional theory. In search of the most stable ground state, we found the ferromagnetic state is at the lowest possible energy state. The structural stability in the cubic phase was assessed from the Goldschmidt tolerance factor, and negative values of formation energies confirmed thermodynamic stability for both compounds. The existence of all positive frequencies in phonon spectra indicates both compounds are thermodynamically stable, and their spin-polarized density of states and band structures revealed the half-metallic ferromagnetism nature. The 100% spin polarization factor and the reasonable magnetic moment values suggest these double-perovskites potential in spintronic applications. Additionally, the thermoelectric response, regarding high power factors suggests these double-perovskites suitability for thermoelectric device applications.

Electronic and Magnetic Properties of the BaTiO$$_{3}$$/LaMnO$$_{3}$$ Interface: a DFT Study

The electronic and magnetic properties of the BaTiO $$_{3}$$ /LaMnO $$_{3}$$ interface were investigated by means of ab initio calculations within the density functional theory (DFT). An impact of the thickness of the ferroelectric overlayer on the interface properties was analysed through the spin-polarized density of states. It was been shown that the band gap decreases with increasing the thickness of ferroelectric overlayer, approaching zero.

Layered TiCl2 Monolayer as an Antiferromagnetic Semiconductor

We report layered TiCl2 monolayer to be a robust antiferromagnetic (AFM) semiconductor by investigating its geometry, stability, electronic and magnetic properties using first-principles calculation and Monte Carlo (MC) simulation. The TiCl2 monolayer exfoliated from layered TiCl2 bulk is verified to be an AFM semiconductor with a relatively wide band gap by spin-polarized density of states and energy band structure calculations. Phonon dispersion and elastic modulus calculations show that the TiCl2 monolayer is dynamically and mechanically stable, respectively. The Néel temperature is evaluated to be 368[Formula: see text]K by MC simulation based on Ising model. Additionally, the band gap, the magnetic moment of a single Ti atom and the Néel temperature can be significantly tuned by applied biaxial strain, but the AFM semiconducting behavior is robust against the applied strains, indicating that the TiCl2 monolayer is a potential candidate for high-speed AFM spintronic applications.

Ab initio расчет зонной структуры и свойств модификаций соединения Ti-=SUB=-3-=/SUB=-Sb, допированного литием

Using the density functional theory (DFT) in the local electron spin density approximation (LSDA), 2×2×2 supercells based on the Ti3Sb compound have been studied. The supercells contained their own vacancies and doped lithium atoms replacing Ti and/or Sb. The DFT-LSDA method was used to calculate the structural, electronic, and magnetic properties, the enthalpy of formation, and the cohesion energy of supercells of two modifications of the Ti3Sb compound. We studied supercells with cubic system (A15 type structure; a = 5.217 Å) and tetragonal system (D8_m type structure; а = 10.457 Å, с = 5.258 Å). It has been established that the distribution of the density of states of the Ti3Sb cubic system has a more metallic character than for the D8_mTi3Sb modification. The enhancement of "metallicity" in the cubic modification A15 Ti3Sb is associated with an increase in the Ti–Sb interatomic distance in the crystal. Due to this, the degree of metallic bonding increases during the electronic interaction between Ti and Sb atoms near the Fermi level in Ti3Sb. In DFT calculations, the spin-polarized density of states was taken into account. It has been established that in both modifications (A15 and D8_m) of Ti3Sb near the Fermi level for s, p, d-states with spin "up" and spin "down" there is a spin imbalance in the population of energy levels. Defect-containing supercells based on Ti3Sb were studied by DFT-LSDA calculations. It is shown that Ti and/or Sb vacancies in the lattices of Ti3Sb crystals of both modifications (A15 and D8_m) increase the magnetic moment (M) as compared to the value of M (M_tot = 0.08 μ_B) of a “pure” Ti3Sb crystal. Considering that Al5 Ti3Sb is also interesting as a material for Li-ion batteries, we studied Ti3Sb–Li supercells doped with lithium. Li-doping and the creation of own Ti and/or Sb vacancies changes the distance between atoms in Ti3Sb. Correspondingly, the resulting local magnetic moments near the Ti or Sb vacancies also change. The enthalpy of formation and magnetic moment of Ti3Sb and Ti3Sb–Li based supercells are calculated. DFT calculations of the structural stability of binary compounds (phases) have been carried out, and the stability of conodes between phases in the Ti–Sb–Li system has been established. The isothermal section of the Ti–Sb–Li system was plotted at 298 K. It is shown that the introduction of various lithium concentrations (<6.25 at. % Li) into the Ti3Sb (Space group Pm3 ̅n; № 223; a = 5.217 Å) crystal lattice reduces the partial magnetic moment of Ti in the Ti3Sb–Li supercell.

Ab initio calculation of the band structure and properties of modifications of the Ti-=SUB=-3-=/SUB=-Sb compound doped with lithium

Using the density functional theory (DFT) in the local electron spin density approximation (LSDA), 2x2x2 supercells based on the Ti3Sb compound have been studied. The supercells contained their own vacancies and doped lithium atoms replacing Ti and/or Sb. The DFT-LSDA method was used to calculate the structural, electronic, and magnetic properties, the enthalpy of formation, and the cohesion energy of supercells of two modifications of the Ti3Sb compound. We studied supercells with cubic system (A15 type structure; a=5.217 Angstrem) and tetragonal system (D8m type structure; a=10.457 Angstrem, c=5.258 Angstrem). It has been established that the distribution of the density of states of the Ti3Sb cubic system has a more metallic character than for the D8m Ti3Sb modification. The enhancement of "metallicity" in the cubic modification A15 Ti3Sb is associated with an increase in the Ti-Sb interatomic distance in the crystal. Due to this, the degree of metallic bonding increases during the electronic interaction between Ti and Sb atoms near the Fermi level in Ti3Sb. In DFT calculations, the spin-polarized density of states was taken into account. It has been established that in both modifications (A15 and D8m) of Ti3Sb near the Fermi level for s-, p-, d-states with spin "up" and spin "down" there is a spin imbalance in the population of energy levels. Defect-containing supercells based on Ti3Sb were studied by DFT-LSDA calculations. It is shown that Ti and/or Sb vacancies in the lattices of Ti3Sb crystals of both modifications (A15 and D8m) increase the magnetic moment (M) as compared to the value of M (M=0.08 μB) of a "pure" Ti3Sb crystal. Considering that Al5 Ti3Sb is also interesting as a material for Li-ion batteries, we studied Ti3Sb-Li supercells doped with lithium. Li-doping and the creation of own Ti and/or Sb vacancies changes the distance between atoms in Ti3Sb. Correspondingly, the resulting local magnetic moments near the Ti or Sb vacancies also change. The enthalpy of formation and magnetic moment of Ti3Sb and Ti3Sb-Li based supercells are calculated. DFT calculations of the structural stability of binary compounds (phases) have been carried out, and the stability of conodes between phases in the Ti-Sb-Li system has been established. The isothermal section of the Ti-Sb-Li system was plotted at 298 K. It is shown that the introduction of various lithium concentrations (≤6.25 at.% Li) into the Ti3Sb (Space group Pm3 n; N 223; a=5.217 Angstrem) crystal lattice reduces the partial magnetic moment of Ti in the Ti3Sb-Li supercell. Keywords: Ti3Sb intermetallic compounds, A15 cubic modification, D8m tetragonal modification, doping with lithium, Ti3Sb-Li, DFT-LSDA calculations, supercell, electronic and magnetic properties, Ti-Sb-Li phase stability.

Spin-dependent Optical Excitations in LiFeO2.

The three-dimensional ternary LiFeO2 compound presents various unusual properties. The main features are thoroughly explored by using many-body perturbation theory. The concise physical/chemical picture, the critical spin polarizations, and orbital hybridizations in the Li–O and Fe–O bonds are clearly examined through geometric optimization, quasi-particle energy spectra, spin-polarized density of states, spatial charge densities, spin-density distributions, and strong optical responses. The unusual optical transitions cover various frequency-dependent absorption structures, and the most prominent plasmon modes are identified from the dielectric functions, energy loss functions, reflectance spectra, and absorption coefficients. Optical excitations are anisotropic and strongly affected by excitonic effects. The close combinations of electronic, magnetic, and optical properties allow us to identify the significant spin polarizations and orbital hybridizations for each available excitation channel. The lithium ferrite compound can be used for spintronic and photo-catalysis applications.

Investigation of the Magnetic and Electronic Properties of Pyrrolic N-doped Graphene Using Density Functional Theory

Modifying the bandgap and magnetic properties of graphene is one of the keys to realizing graphene-based nanodevices. Here, we investigate the effect of nitrogen concentration in the pyrrolic bond configuration on the magnetic properties of graphene using the spin-polarized Density Functional Theory (DFT) method. For a better understanding, we also calculated the electronic and structural properties of the pyrrolic N-doped graphene. This study used three models, i.e., pristine graphene and pyrrolic N-doped graphene with two nitrogen concentrations (N x G1 − x , x=2.000% and 3.125%). We observed that the higher the dopant concentration, the more the deformation of the planar structure in pyrrolic N-doped graphene. This is indicated by the more wrinkled structure that forms. Semi-metal to metal transitions were also observed in both models of pyrrolic N-doped graphene. Asymmetry behavior in the spin-polarized density of states (SPDOS) was also observed in both pyrrolic N-doped graphene models. The total magnetic moment increases with increasing dopant concentration. At a concentration of 2.000%, the resulting total magnetic moment is 1.68 µB/cell, and at a concentration of 3.125%, it is 1.74 µB/cell. We suggest that defects and nitrogen impurities play a crucial role in the transition of the magnetic properties of graphene. Our result shows that nitrogen-doped graphene with pyrrolic configuration is a promising candidate for nanomagnetic devices.

Predicted half-metallicity and ferromagnetism in the Fe (III) doped BaZrO3 perovskite: A theoretical insight

The variance in the magnetoelectric behavior of BaZrO3 owing to the doping of Fe (III) on the Zr-site has been studied based on density functional calculations. We can predict the structural parameters, electronic structure, and ferromagnetic properties of BaFexZr1−xO3 precisely deprived of considering any strong correlation effect in the calculations. The equilibrium structural parameters are accounted to be in concurrence with the former theoretical and experimental investigations. It is observed that the structural phase remained semiconducting cubic (Pm-3m) up to 12.5% of Fe content and transformed to a conducting tetragonal phase (P4/mmm) beyond that. Spin-polarized density of states and band-structure calculations have probed that pristine BaZrO3 is a wide-bandgap semiconductor and in a nonmagnetic state. The ground-energy-state of Fe3+ doped BaZrO3 compounds varies from half-metal to metal in a ferromagnetic state. In particular, the present calculations have correctly predicted half-metallicity in BaFexZr1−xO3 when doping concentrations were 12.5% and 25%. The half-metallic gap ΔHM, which is the minimum of the lowest energy level of minority spin conduction bands relative to the Fermi level, and the absolute values of the topmost energy level of minority spin valence bands are estimated to be 0.55 eV in BaFe0.25Zr0.75O3 and 0.44 eV in BaFe0.5Zr0.5O3.

Unraveling the formation mechanism of hydrogenated vacancy at γ-Ni/γ'-Ni3Al phase interface and its roles in interfacial stability and strength

γ/γ' phase interfaces are hidden troubles that threaten the service safety of Ni-based single crystal superalloys due to their thermodynamic instabilities and lower mechanical strengths. To gain insights into the role of hydrogenated vacancy in the stability and cohesion of γ/γ' interfaces, the formation mechanism of hydrogenated vacancy at (001) γ-Ni/γ'-Ni3Al interface and its influences on interfacial stability and fracture strength were systematically studied by using first-principles calculations. Our results show that the short-range interplay between monovacancy and single hydrogen atom at (001) γ-Ni/γ'-Ni3Al interface causes the formation of Vac-H complex structure (i.e., hydrogenated vacancy) as separated by a certain distance rather than a direct recombination. The hydrogen atom in the first nearest-neighbor interstices of Ni vacancy (site 6) deviates from the interstitial centers to the vacancy, owing to the interattraction between monovacancy and hydrogen atom. The formation of hydrogenated vacancy at (001) γ-Ni/γ'-Ni3Al interface can promote the interfacial thermodynamic stability as compared with the vacancy-containing γ/γ' interface, but weaken the interfacial fracture strength and change the preferable fracture place of γ/γ' interface. The underlying mechanisms of stabilizing and weakening effects on the γ/γ' interface were revealed by using spin-polarized density of states and differential charge densities.

First principles calculations of 3d-4d transition metal based LiMgPdSn–type FeCrRuZ (Z = Al, Ga, In, Si) equiatomic quaternary Heusler alloys

We have investigated the structural, electronic and magnetic properties of the equiatomic quaternary Heusler (EQH) alloys FeCrRuZ (Z = Al, Ga, In, Si) using density functional theory. The structural study reveals that all the FeCrRuZ (Z = Al, Ga, In, Si) alloys stabilized to Y1 type structural configuration with ferrimagnetic ordering. The spin-polarized density of states (DOS) calculation demonstrates that FeCrRuAl alloy exhibits unusual spin-gapless half-metallic (SG-HM) behavior with majority spin-up channel possessing metallic characteristic and minority spin-down channel showing spin-gapless nature. The FeCrRuSi, FeCrRuGa and FeCrRuIn alloys display half-metallic, nearly half-metallic and metallic nature, respectively. The FeCrRuAl and FeCrRuSi alloys greatly follow the Slater-Pauling rule and give 100% spin-polarization at the Fermi level with total integer magnetic moment of 1 and 2 μB, respectively. In all, the total magnetic moment of FeCrRuZ (Z = Al, Ga, In, Si) alloys is contributed mainly by Cr atoms. The origin of the half-metallic band gap is elucidated through a schematic molecular orbital (MO) diagram. Further, the role of main group elements on structural, electronic, magnetic and half-metallic properties are explored in greater detail.

Electronic structure of REFe2 (RE = Dy, Ho and Er) intermetallic compounds: Ab initio spin-density functional theory

In this study, the structural, magnetic and electronic characteristics of the cubic MgCu2-type binary Laves phases REFe2 (RE = Dy, Er and Ho) compounds have been investigated. To describe the correlation effects with high accuracy, the spin density functional theory (DFT) was used within the generalized gradient approximation (GGA) to estimate the exchange correlation potential and the GGA + U (U: Hubbard parameter) calculations. The parameter of the lattice and magnetic moments at the equilibrium state were found to be in good agreement with the available experimental data. We have calculated the magnetic moments of RE (RE = Dy, Er and Ho) and Fe in their binary compounds, by using GGA and GGA + U methods. The value of the Fe magnetic moments was found to be higher than that of RE. The obtained results have also shown that the GGA + U method is the best to describe our systems. We have also projected the electronic structures and the spin-polarized density of states (DOS) of the RE-4f and Fe-3d orbital. The REFe2 compound has shown to exhibit a metallic behavior with a small spin-down electronic density of states at the Fermi level in both the GGA and GGA + U approximations.

Effect of addition of Co on the magnetic properties of MnSb

The influence of addition of Co on the structural and magnetic properties of MnSb was investigated. The compound formed in the NiAs-type hexagonal structure. Addition of Co to MnSb causes changes in both the lattice parameters. It was observed, from magnetization measurements, that both Curie temperature and saturation magnetization decrease from those of MnSb. The spin-polarized density of states (DOS) calculations revealed that the intermetallic compound favors ferromagnetic ground state even after as much as 0.25 atom of Co per formula unit of MnSb. Charge transfer takes place from the interstitial Co-atom to minority spin band of Mn-atom resulting in an increase in the DOS compared to MnSb at the Fermi level. MnSbCo0.25 exhibits a negative magnetocaloric effect with the largest change in the entropy value, ΔSm = 2.5 J. kg-1. K-1 (for a change in magnetic field from 0 to 5 T), across the second order phase transition at 292 K. The change in the value of magnetic entropy is low around the phase transition and might be due to the small magnetic moment of Mn-atom.

A DFT study on the electronic and magnetic properties of triangular graphene antidot lattices

We explore the effect of antidot size on electronic and magnetic properties of graphene antidot lattices from first-principles calculations. The spin-polarized density of states, band gap, formation energy and the total magnetization of two different equilateral triangular and right triangular antidots with zigzag and mixed zigzag-armchair edges are studied. We find that although the values of band gap, formation energy and the total magnetization of both structures are different, these values may increase when the number of zigzag edges is increased. The armchair edges have no contribution in the total magnetization of right triangular antidots. The induced magnetic moments are mainly localized on the edge atoms with a maximum value at the center of each side of the triangles. We show that a spin-dependent band gap opens up in bilayer graphene as a result of antidot pattern in only one layer of the structure. Such periodic arrays of triangular antidots that cause a spin-dependent band gap around the Fermi energy can be utilized for turning graphene from a diamagnetic semimetal into a magnetic semiconductor.

Manipulation of the magneto-optical properties of a Co/C heterostructure under an applied voltage

In this work, electrical manipulation of the magneto-optical properties of a cobalt (Co)/carbon (C) heterostructure is demonstrated via reversible voltage (V)-dependent magnetic circular dichroism (MCD) measurements to provide information on its spin-polarized density of states. Complex impedance spectroscopy revealed the occurrence of capacitance effects between Co and C. Suppression of the radial distribution functions of the X-ray absorption spectra and changes in the Raman spectra reveal that charge injection under an applied V results in increased interstitial charge densities. Angle-dependent changes in MCD under an applied V reveal that variations in C–Co hybridization due to charge accumulation are responsible for the observed phenomena.

Studies on the structural stability of Co2P2O7 under pressure

The crystal structural evolution of Co2P2O7 was studied by using in situ high pressure angle dispersive x-ray diffraction with synchrotron radiation. The results demonstrate that the α phase of Co2P2O7 goes through a partially irreversible structural transformation to β phase under pressure. The pressure is conductive to reduce the longest CoO bond length of the α phase, and then more uniform CoO bonds and regular hexagonal arrangement of CoO6 octahedra of the β phase are favored. According to the Birch-Murnaghan equation, the fitted bulk modulus B0 is 158.1(±5.6) GPa for α phase and 276.5(±6.5) GPa for β phase. Furthermore, the first-principles calculations show that these two phases of Co2P2O7 have almost equal total energies, and also have similar band structures and spin-polarized density of states at their ground states. This may be the reason why these two phases of Co2P2O7 can coexist in the pressure released state. It is found that the band gap energies decrease with increasing pressure for both phases.