Perdew Burke Ernzerhof Generalized Gradient Approximation Research Articles

Analysis of structural, electronic and optical properties of Er-doped rock salt AlN using ab-initio calculations.

This investigation includes the structural and optoelectronic characteristics of both pure and Er-doped rock salt aluminium nitride (AlN). Upon introducing Er doping into the AlN host, the calculations reveal a rise in the atomic parameter. Incorporating Er into the system leads to enhancements in the static dielectric coefficient ɛ1(0), static reflectivity R(0), as well as static refractive index n(0), at zero frequency. After doping, the peaks of imaginary dielectric tensor, extinction coefficient and absorption coefficient shift towards lower energy levels. Various exchange correlation potentials are incorporated to compare the results of electronic and optical characteristics. We employed the full potential linearized augmented plane wave (FP-LAPW) approach with WIEN2k code in conjunction with the density functional theory (DFT). To explore the optoelectronic characteristics of both pure as well as doped systems, three distinct exchange correlation potentials are utilized: the Perdew-Burke-Ernzerhof Generalized Gradient Approximation (PBE-GGA), Modified Becke Johnson Generalized Gradient Approximations (mBJ + GGA) and Hubbard potential (GGA + U).

Symmetry breaking and self-interaction correction in the chromium atom and dimer.

Density functional approximations to the exchange-correlation energy can often identify strongly correlated systems and estimate their energetics through energy-minimizing symmetry-breaking. In particular, the binding energy curve of the strongly correlated chromium dimer is described qualitatively by the local spin density approximation (LSDA) and almost quantitatively by the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA), where the symmetry breaking is antiferromagnetic for both. Here, we show that a full Perdew-Zunger self-interaction-correction (SIC) to LSDA seems to go too far by creating an unphysical symmetry-broken state, with effectively zero magnetic moment but non-zero spin density on each atom, which lies ∼4eV below the antiferromagnetic solution. A similar symmetry-breaking, observed in the atom, better corresponds to the 3d↑↑4s↑3d↓↓4s↓ configuration than to the standard 3d↑↑↑↑↑4s↑. For this new solution, the total energy of the dimer at its observed bond length is higher than that of the separated atoms. These results can be regarded as qualitative evidence that the SIC needs to be scaled down in many-electron regions.

Thermodynamic properties of rhodium—A first principle study

The high-pressure and high-temperature thermodynamic properties of rhodium (up to 2000 K and 300 GPa) are presented using the first principle approach within the quasi-harmonic approximation. The thermal Helmholtz free energy includes the contribution of both phonon vibrations and electronic excitations. The performance of three popular exchange-correlation functionals—local density approximation [Perdew et al., Phys. Rev. B 23, 5048 (1981)], Perdew–Burke–Ernzerhof generalized gradient approximation (PBE) [Perdew et al., Phys. Rev. Lett. 77, 3865 (1996)], PBE modified for dense solids [Perdew et al., Phys. Rev. Lett. 100, 136406 (2008)] are shown. The simulated thermal expansion coefficient, isobaric heat capacity, mode-Grüneisen parameter, thermodynamic average Grüneisen parameter, and bulk modulus are compared with the available experimental and theoretical reports. The contribution of thermal electronic excitations to the obtained thermodynamic parameters is significant at low pressure and high temperatures, except in bulk modulus, where it is small. The pressure-dependent elastic constant coefficient (Cij) and the Debye temperature are computed at 0 K. The Pugh ratio calculated from Cij indicates that rhodium undergoes brittle to ductile transitions at an average pressure of 7.45 GPa.

Strain tuned structural, mechanical, electronic, and optical properties of lead-free oxy-nitride SrTaO2N perovskite using first-principles study

Recent advancements in perovskite-based solar energy conversion technologies require materials having enhanced optoelectronic properties and stability. Harnessing density functional theory (DFT), we have investigated here a novel orthorhombic phase of a recently synthesized oxynitride perovskite, SrTaO2N, and its uniaxial strain-tunable electronic and optical properties. Phonon dispersion and formation energy calculations are utilized to determine lattice dynamic stability and exothermic formation feasibility of the structure, correspondingly. The predicted bandgap at the Heyd–Scuseria–Ernzerhof [generalized gradient approximation Perdew–Burke–Ernzerhof (GGA-PBE)] level is ∼2.125 eV (∼1.125 eV), which is highly receptive to uniaxial strains. The bandgap formed in between X and G points with high symmetry at the first Brillouin zone was further dissected using the atomic orbital projected density of states (PDOS). The PDOS showed that the N-pz orbital dominantly contributes to valence band maxima and the Ta-dz2 orbital to conduction band minima. Compressive uniaxial strain widens the bandgap by ∼1.21 times, while tensile uniaxial strain lowers the bandgap by ∼1.1 times from the intrinsic value, suggesting strain switchable bandgap nature in the material. An elastic constant matrix also evaluates the mechanical stability of strained structures, and we found that in the strained structures from −6% to +6%, SrTaO2N is mechanically stable and ductile. Optical absorption reveals an increased absorption coefficient in the visible spectrum. These strain-tuned optoelectronic properties through the DFT approach thus suggest an evident route to a wide range of optoelectronics applications of the SrTaO2N perovskite material.

Scintillator efficiency enhancement potential consequent to the pressure-dependent electronic, optical and elastic properties of CaI2: first-principles calculations

ABSTRACT First-principles calculations are carried out to investigate the effect of pressure (up to 40 GPa) on electronic, optical and elastic properties of the scintillator material calcium iodide, CaI2, by using Perdew–Burke–Ernzerh of generalized gradient approximation (PBE-GGA). The electronic band structure reveals an indirect band gap of 3.89 eV and a direct band gap of 4.35 eV for zero pressure. We have also calculated the pressure dependence of optical properties. The elastic constants and elastic moduli increase nonlinearly with pressure. Decreasing Pugh’s ratio and increasing hardness with pressure indicate a cross-over from ductile to brittle nature at 5 GPa. Analyses of elastic properties show that CaI2 is mechanically stable up to the applied pressure of 40 GPa. The calculated light yield increases linearly with pressure yielding a pressure coefficient of 1327 ph/MeV per GPa due to the decreasing band gap. Light yield increases as much as 62% at 40 GPa.

A DFT study of bandgap tuning in chloro-fluoro silicene.

The structural, electronic and optical properties of silicene and its derivatives are investigated in the present work by employing density functional theory (DFT). The Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) is used as the exchange-correlation potential. Our results provide helpful insight for tailoring the band gap of silicene via functionalization of chlorine and fluorine. First, relaxation of all the materials is performed to obtain the appropriate structural parameters. Cl-Si showed the highest lattice parameter 4.31 Å value, while it also possesses the highest buckling of 0.73 Å among all the derivatives of silicene. We also study the electronic charge density, charge difference density and electrostatic potential, to check the bonding characteristics and charge transfer between Si-halides. The electronic properties, band structures and density of states (DOS) of all the materials are calculated using the PBE-GGA as well as the modified Becke-Johnson (mBJ) on PBE-GGA. Pristine silicene is found to have a negligibly small band gap but with the adsorption of chlorine and fluorine atoms, its band gap can be opened. The band gap of Cl-Si and F-Si is calculated to be 1.7 eV and 0.6 eV, respectively, while Cl-F-Si has a band gap of 1.1 eV. Moreover, the optical properties of silicene and its derivatives are explored, which includes dielectric constants ε1 and ε2, refractive indices n, extinction coefficients k, optical conductivity σ and absorption coefficients I. The calculated binding energies and phonon band structures confirm the stability of Cl-Si, Cl-F-Si, and F-Si. We also calculated the photocatalytic properties which show silicine has a good response to reduction, and the other materials to oxidation. A comparison of our current work to recent work in which graphene was functionalized with halides, is also presented and we observe that silicene is a much better alternative for graphene in terms of semiconductors and photovoltaics applications.

First-principles calculations investigating structural, electronic optical and elastic properties of ABSe3 (A = Rb, Cs) compounds explored for photovoltaic and optoelectronics applications

In few recent years, great and significant efforts are devoted from researcher all over the world to pursue the revolution of photovoltaic’s materials and their uses in various applications. In the present work, a series of ab-initio simulations based on the density functional theory DFT plane wave pseudo-potential (PW-PP) method and hence performed towards the perselenoborate materials ABSe3 (A = Rb,Cs) for the first time along the three main polarizations of the incident wave directions [100], [010] and [001] with the aim of exploring their structural, electronic, optical and elastic properties. The generalized gradient approximation Perdew–Burke–Ernzerhof (GGA-PBE) carried out with CASTEP code is used for the exchange–correlation potential. The computed results showed that the structural properties of investigated compounds are very good agreement to the available experimental data, showing that the current calculations are quite accurate. Moreover, the density of states and electronic band structure calculations reveal that RbBSe3 (CsBSe3) compounds exhibit direct band gap semiconductor nature 1.66 eV (1,82 eV) respectively within the optimal range band gap 1eV–2eV required for photovoltaic’s applications makes them having great potential to obtain efficient Perovskite solar cell PSC. Additionally, our finding optical properties calculations reveal that the two investigated compounds exhibit strong absorption (prominent absorption peaks up 2,4 × 105cm−1) in UV range, while the real part of the refractive index for RbBSe3 (CsBSe3) was 2.62 (2.60) respectively which might be beneficial for photovoltaic application (top cell in solar cell) and optical applications. Also, high optical conductivity (∼1015sec−1) is found to be observed in visible ultraviolet range (1.7 eV to 30 eV). The lower reflectivity seen by RbBSe3 compared to CsBSe3 in the larger energy spectrum of electromagnetic radiation suggests that RbBSe3 compound is more suitable for electronic applications. Further, once the elastic constants are obtained, the calculated mechanical properties, bulk modulus (B), shear modulus (G), the ratio B/G, Young’s modulus (E), Poisson’s ratio (ν), anisotropy universal (AU) are calculated. Our calculated Young’s modulus indicate that the CsBSe3 is less hardness compared to RbBSe3, while Poisson’s ratio calculated leads them to have a character ionic and RbBSe3 is more ductile than CsBSe3. The calculation value of θ D predicted from elastic constants appears low which is closely related to many physical properties such as specific heat and melting temperature. Finally, the finding results reveal another way of investigating mechanical stability, where both compounds are mechanically stable since all elastic constant computed are perfectly satisfied the Born stability criteria, flexible and brittle. Finally, we hope that all these results will be helpful for designing photovoltaic and optoelectronic devices.

Theoretical investigation of optoelectronic properties of Al-doped BAs using TB-mBJ approach

For quite a long time, the scientific community has been searching for a material that surpasses the existing material systems in terms of energy conversion efficiency for photovoltaic applications. In this study, the optoelectronic properties of pure and Al-doped boron arsenide B[Formula: see text]Al[Formula: see text]As [Formula: see text] in the zinc blende (ZB) structure were systematically examined using the density functional theory (DFT) and the Modified Becke–Johnson (TB-mBJ) exchange correlation (XC) potential. The Perdew–Burke–Ernzerhof generalized gradient approximation (PBE) functional was used for structural optimization. After considering the ground state lattice constant of 4.82[Formula: see text]Å then calculating the bandgap energy of pure BAs, which are consistent with experimental and theoretical findings, we estimated the basic electronic and optical characteristics of Al-doped boron arsenide, including band structures, electronic density of state, dielectric function, refractive index, extinction coefficient, absorption and optical conductivity. The unusual and interesting optoelectronic features of the investigated compounds revealed in this work offer substantial promise for improving the energy conversion efficiency of solar cells.

Study of structural, elastic, electronic, optical and magnetic properties of Heusler Mn2NiAl: Ab initio calculations

In this paper, we will investigate the structural, electronic, mechanical, magnetic and optical properties of Heusler Mn2NiAl (MNA) compound using the Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) of the full potential linearized augmented plane-wave method for exchange and use correlations, modified Becke–Johnson and GGA+U Hubbard parameter. The calculated band structure (BS) and density of states (DOS) of MNA showed a metallic (GGA), nearly half-metallic (mBJ) and half metallic (GGA+U) behavior. Moreover, the magnetic computed magnetic moments by GGA+U are higher compared to GGA and mBJ results. Bulk modulus, shear modulus, Voigt and Reuss polycrystalline elastic modulus, Debye temperature, sound velocities, the melting temperatures, [Formula: see text] ratio, Young’s modulus and Poisson’s ratio were obtained. The elastic anisotropy of MNA alloy was analyzed using 2D and 3D figures of directional dependence of Poisson’s ratio, shear modulus, linear compressibility and Young’s modulus. Studies have shown that the Heusler material MNA has magnetic and anisotropic properties and is mechanically stable.

Investigating Electronic, Optical, Thermodynamic, and Thermoelectric Properties of SrO and SrO2 Phases: A Density Functional Theory Approach.

The significance of strontium oxide (SrO) and strontium peroxide (SrO2) is currently being investigated as one of the countless potential uses for green energy. However, few studies have examined the distinctive properties of several phases of SrO and SrO2. In order to fill this research gap, we have conducted a study on their various properties through "density functional theory (DFT)" under ideal conditions. This includes the study of electronic, optical, thermodynamic, and thermoelectric properties of the above-mentioned materials. For this study, the "Quantum Espresso" tool in DFT using Perdew-Burke-Ernzerhof-generalized-gradient approximation (PBE-GGA) as the exchange-correlation functional and "Optimized Norm-Conserving Vanderbilt (ONCV)" as the pseudopotential has been used. The face-centered cubic (FCC), body-centered cubic (BCC), hexagonal-1, and hexagonal-2 phases of SrO and the tetragonal and orthorhombic phases of SrO2 have been selected for the aforesaid study, for which some structural information has already been available. During this study, the energy band gap as an electronic property; the dielectric constant, refractive index, absorption coefficient, reflectivity, and energy loss function as optical properties; entropy, heat capacity, Debye temperature, and Debye sound velocity as thermodynamic properties; and the Seebeck coefficient, thermal conductivity, electrical conductivity, and figure of merit as thermoelectric properties have been investigated. In addition, phonon dispersion curves and formation energies have been used to confirm the dynamical stability and thermodynamic stability, respectively, for all of the materials mentioned above. The curve showed that the FCC, hexagonal-1, and hexagonal-2 phases of "SrO" are dynamically stable. These materials have good optoelectronic properties and can be used in ultraviolet sensors due to their intermediate band gap and highest material response in the ultraviolet range. In terms of thermoelectric property, the maximum value of "figure of merit" for the above material has been achieved up to 0.5. Satisfactory agreement has been found between the current findings and the known theoretical and experimental findings.

Exploration of the structural, optoelectronic, magnetic, elastic, vibrational, and thermodynamic properties of molybdenum-based chalcogenides A2MoSe4 (A =Li, K) for photovoltaics and spintronics applications: a first-principle study.

In the present work, the cubic phase of the chalcogenide materials, i.e., A2MoSe4 (A =Li, K) is examined to explore the structural, optoelectronic, magnetic, mechanical, vibrational, and thermodynamic properties. The lattice parameters for Li2MoSe4 are found to be a= 7.62 Å with lattice angles of α=β=γ=90° whereas for K2MoSe4, a= 8.43 Å, and α=β=γ=90°. These materials are categorized as semiconductors because Li2MoSe4 and K2MoSe4 exhibit direct energy band gap worth 1.32 eV and 1.61 eV, respectively through HSE06 functional. The optical analysis has declared them efficient materials for optoelectronic applications because both materials are found to be effective absorbers of ultraviolet radiations. These materials are noticed to be brittle while possessing anisotropic behavior for various mechanical applications. The vibrational properties are explored to check the thermal stability of the materials. On the basis of thermodynamics and heat capacity response, Li2MoSe4 is more stable than K2MoSe4. The results of our study lay the groundwork for future research on the physical characteristics of ternary transition metal chalcogenides (TMC). These physical properties are explored for the first time while using a first-principles approach based on density functional theory (DFT) in the framework of Cambridge Serial Total Energy Package (CASTEP) by Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) functional. However, GGA+U and HSE06 are also employed to improve electronic properties. Kramers-Kronig relations are used to evaluate the dielectric function with a smearing value of 0.5 eV. Voigt-Reuss-Hill approximation is used for seeking the elastic response of these materials. The thermodynamic response is sought by harmonic approximation. The density functional perturbation theory (DFPT) approach is used for investigating atomic vibrations.

Mechanical, Magnetic, and Optical Characteristics of Tm‐Based Chalcogenides for Energy‐Harvesting Applications

Herein, a comprehensive theoretical analysis of Tm‐based chalcogenides MgTm2Y4 (Y = S, Se) is performed to understand magnetic, optical, mechanical, and transport characteristics. And, Perdew–Burke–Ernzerhof generalized gradient approximation (PBEsol‐GGA) functional and modified Becke–Johnson (mBJ) potentials are employed while computing the mechanical and spin‐polarized electronic properties, respectively. The structural stability of both spinels is confirmed using formation energy and Born stability criteria. Both spinels are found exhibiting ductile nature according to the computed Pugh's and Poisson's ratios. For observing the room‐temperature ferromagnetism, Curie temperature is calculated. Furthermore, spin‐polarized electronic properties reveal that both spinels exhibit ferromagnetic nature, which is induced due to coupling among Tm‐ and S/Se‐related constituent states. The potential optoelectronic applications are suggested by computing and discussing dielectric constant, refractive index, and absorption coefficient. BoltzTraP code is used to investigate the thermoelectric features of MgTm2Y4 (Y = S, Se) in the 200–800 K temperature range.

First‐Principles Calculations to Investigate Electronic, Elastic, Magnetic, and Optical Properties for B1, B2, and B3 Phase for Sr0.875Mn0.125O with and Without Relaxation Structure

AbstractIn this work, the structural, electronic, elastic, optical, and magnetic properties for the B1, B2, and B3 phases of Sr0.875Mn0.125O with relaxed structure (RS) and unrelaxed structure (URS) are investigated. The investigations are accomplished by the adoption of first‐principle methods established on spin‐polarized density functional theory, based on the full‐potential linearized augmented plane wave method as implemented in the WIEN2k code, where the electronic exchange‐correlation potential is studied by the Perdew–Burke–Ernzerhof generalized gradient approximation (GGA‐PBEsol) and the revised TB‐mBJ rapprochement. The negative formation energy and elastic constant that are acquired indicate the thermodynamical and mechanical stability of all these structures. The ternary Sr0.875Mn0.125O alloys for all structures show half‐metallic ferromagnetic behavior with a spin polarization of 100 % at the Fermi level, except the B2 phase without unrelaxed structure (URS). The total magnetic moments are 5 µB for all compounds and the interaction is ferromagnetic between Mn─Sr and Mn─O sites. Optical properties such as refractive index and the optical reflectivity for these alloys are computed and discussed. These materials are half‐metallic ferromagnets, and they can be desirable applicants for spintronics implementations and ultraviolet spectra.

First-principles calculations to investigate structural, electronic and magnetic anisotropy energy of ZnFe[formula omitted]O[formula omitted] spinel ferrite for spintronics applications

Structural, electronic and magnetic investigations of ZnFe2O4 have been made by using density functional theory with Perdew–Burke–Ernzerhof Generalized-Gradient Approximation as exchange and correlation functional. Additionally, the effect of Hubbard, U, and spin orbit coupling, SOC on electronic and magnetic properties has also been observed. The U-value for Zinc and Iron are used, 6.0 eV (0.44 Ry) and 4.3 eV (0.316 Ry) respectively. The optimized lattice parameter matches well with experimental with mere percentage difference of 0.039%. This optimized lattice constant is used for SCF calculations to calculate the above mentioned properties of zinc ferrite. It is found that zinc ferrite have high value of magnetic moments, 19.721μB, 20.003μB, and 19.580μB for PBE, PBE with Hubbard, and with spin orbit coupling respectively. The magneto crystalline anisotropy energy calculations confirm the utility of this material for spintronics device fabrication.

The spin-polarized electronic and optical properties of novel Ba2TaXO6 (X = Co, Fe, In) for optoelectronic applications: An ab-initio study

First principles calculations were carried out to examine the spin-polarized electronic and optical characteristics of novel Ba2TaXO6 (X = Co, Fe, In) double perovskites in the monoclinic phase, employing the full-potential linearized augmented plane wave technique (FP-LAPW) based on the density functional theory (DFT). To calculate the total energy, the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) were used. The electronic study with the TB-mBJ approach shows a metallic nature for Ba2TaCoO6 and a half-metallic nature for Ba2TaFeO6 and Ba2TaInO6 materials. The calculated density of states, nearly show similar features for all the materials. The PDOS were calculated, which displays the contribution of several electronic states for these compounds in the distribution. Additionally, in the optical spectra, the dielectric functions, absorption coefficients, refractive indexes, extinction coefficients, energy loss function, and reflectivity parameters were calculated in the energy range 0–14 eV. The optical parameters demonstrate that the materials are the potential candidates for opto-electronics devices.

First principles study of the structural, half-metallic ferromagnetism, magnetic, and transport properties of KXO2 (X = Pr, Nd, and Pm) hexagonal oxides

The density functional theory (DFT) studies are made to calculate the electronic, magnetic, and transport characteristics of potassium lanthanide KXO2 (X = Pr, Nd, and Pm) oxides have been studied by using the WIEN2K code. Perdew Burke Ernzerhof-Generalized Gradient approximation (PBE-GGA) is used for the exchange-correlation energy of the crystal structures in the hexagonal phase. However, the volume-optimized graphs depict that these compounds are energetically stable in the ferromagnetic state. Moreover, the studies of the spin-up channels of the band structure and density of states (DOS) reveal their metallic behavior whereas semiconductor nature has been noticed through spin-channels. Therefore, studied materials have half metallicity nature with 100% spin polarization at the Fermi level (EF). Total and partial magnetic moments of KXO2 (X = Pr, Nd, and Pm) and individual atoms exist due to unpaired 4f electronic states of the lanthanide ions, present at the EF. The energy difference between anti-ferromagnetism and ferromagnetism versus the volume optimization curve gives the curie temperature (Tc). The volume optimization curves show a flat region where both magnetic states have similar energies. This means the material can exist at the equilibrium volume in either state. Finally, thermoelectric properties are calculated by the BoltzTraP code. Our results unveil that these potassium-based lanthanide oxides are potential materials for devising spintronics devices and lifting future practical applications.

Electronic Properties, Linear and Nonlinear Performance of KAgCh (Ch = S, Se) Compounds: A First-Principles Study

In the current study, the peculiar nonlinear optical (NLO) properties of KAgCh (Ch = S, Se) and their structural, electronic, and thermodynamic properties are computed utilizing the FP-LAPW (full-potential linearized augmented plane wave) approach as embedded in Wein2K code. The Perdew–Burke–Ernzerh of generalized gradient approximation (PBE-GGA) was considered for the structural optimization. The computed bandgaps are found to be 2.57 and 2.39 eV for KAgS and KAgSe, respectively. Besides the structural and electronic properties, we also computed the refractive indices n(ω), surface energy loss function (SELF), and nonlinear optical susceptibilities. The estimated refractive indices, energy band gap, and their frequency dependence for the investigated KAgCh (Ch = S, Se) compounds, along with the NLO coefficients, are found to be in good agreement with the earlier reports. These current findings suggest that KAgCh (Ch = S, Se) can be recommended for nonlinear optical applications in the near-infrared spectrum.

Investigation of structural, mechanical, dynamic stability and electronic properties of anti-perovskite nitrides ANLa3 (A = Al, Ga): a DFT and DFPT studies

Various properties of anti-perovskites ANLa3 (A = Al, Ga) are investigated using the density functional theory (DFT). The GaNLa3 properties are studied for the first time. The computed lattice parameter of AlNLa3 is found to be close to other theoretical and experimental results. The mechanical stability of the present compounds are confirmed by the elastic constants estimated through the calculations. Furthermore, bulk modulus, shear modulus and Young’s modulus are evaluated. In this report, the dynamic stability and formation energy of AlNLa3 and GaNLa3 alloys are also highlighted. The state density functional perturbation theory (DFPT) is used to reveal the phonon calculation showing that the studied compounds are dynamically stable. Indeed, with a negative formation energy, it has been predicted that the GaNLa3 compound can be synthesized experimentally. Moreover, the electronic properties are studied using the Perdew–Burke–Ernzerhof Generalized Gradient Approximation (GGA-PBE) as well as a more sophisticated exchange-correlation Yukawa Screened PBE0 (YS-PBE0) hybrid functional.It has been found that the computed energy band structures within both approaches, that the anti-perovskites AlNLa3 and GaNLa3 are metallic nature. The total density of states (TDOS) and partial density of states (PDOS) are also calculated to show in evidence the contribution of atoms orbitals in the formation of bands.

Role of spin-orbit coupling effects in rare-earth metallic tetra-borides: a first principle study

We have investigated the electronic structure of rare-earth tetraborides, $\textrm{RB}_{4}$, using first-principle electronic structure methods (DFT) implemented in Quantum Espresso (QE). In this article we have studied heather-to neglected strong spin-orbit coupling (SOC) effects present in these systems on the electronic structure of these system in the non-magnetic ground state. The calculations were done under GGA and GGA+SO approximations using ultrasoft pseudopotentials and fully relativistic ultrasoft pseudopotentials (for SOC case). Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) exchange-correlation functionals within the linearized plane-wave (LAPW) method as implemented in QE were used. The projected density of states consists of 3 distinct spectral peaks well below the Fermi energy and separated from the continuum density of states around the Fermi energy. The discrete peaks arises due to rare-earth $s$-orbital, rare-earth $p$ + B $p$ and B $p$-orbitals while the continuum arises due to hybridized B $p$, rare-earth $d$ orbitals. Upon inclusion of SOC the peak arising due to rare-earth $p$-orbitals gets split into two peaks corresponding to $j=0.5$ and $j=1.5$ configurations. In case of $\textrm{LaB}_{4}$, in the presence of SOC, spin-split $4f$ orbitals contributes to density of states at the Fermi level while the density of states at the Fermi level largely remains unaffected for all other materials under consideration.

Spin-state gaps and self-interaction-corrected density functional approximations: Octahedral Fe(II) complexes as case study.

Accurate prediction of a spin-state energy difference is crucial for understanding the spin crossover phenomena and is very challenging for density functional approximations, especially for local and semi-local approximations due to delocalization errors. Here, we investigate the effect of the self-interaction error removal from the local spin density approximation (LSDA) and Perdew-Burke-Ernzerhof generalized gradient approximation on the spin-state gaps of Fe(II) complexes with various ligands using recently developed locally scaled self-interaction correction (LSIC) by Zope et al. [J. Chem. Phys. 151, 214108 (2019)]. The LSIC method is exact for one-electron density, recovers the uniform electron gas limit of the underlying functional, and approaches the well-known Perdew-Zunger self-interaction correction (PZSIC) as a particular case when the scaling factor is set to unity. Our results, when compared with reference diffusion Monte Carlo results, show that the PZSIC method significantly overestimates spin-state gaps favoring low spin states for all ligands and does not improve upon density functional approximations. The perturbative LSIC-LSDA using PZSIC densities significantly improves the gaps with a mean absolute error of 0.51eV but slightly overcorrects for the stronger CO ligands. The quasi-self-consistent LSIC-LSDA, such as coupled-cluster single double and perturbative triple [CCSD(T)], gives a correct signof spin-state gaps for all ligands with a mean absolute error of 0.56eV, comparable to that of CCSD(T) (0.49eV).