Local Density Approximation Research Articles

Exploring the multifaceted properties of novel oxide-based perovskites ABO3 (A=Nd and B[dbnd]Lr, Y): A DFT study

The full-potential linear augmented plane wave with local orbital (FP-LAPW) technique is now used in this approach to better understand the structural, electronic, optical and mechanical properties of simple cubic oxide perovskite. NdLrO3 and NdYO3 compounds are studied by employing the density functional theory (DFT) with CASTEP code for the first time. The lattice parameters are found 4.2462 and 4.2301 Å for NdLrO3 and NdYO3 respectively. Both the compounds have 1.9 eV and 1.4 eV band gap showing the direct band gap nature of both materials. The exchange-correlation (XC) energy has been selected during this investigation with the Local Density Approximation (LDA) approach. We optimize as well as clarify the elastic constants Cij, the bulk modulus B, elasticity modulus G, Young's modulus of stretch Y, and the Poisson ratio v. Every substance shows anisotropic behavior. NdLrO3 and NdYO3 compounds exhibit a direct band-gap nature, as revealed by the electronic band structure computations. These compounds were all classified as semiconductors. To quantify the number of localized electrons in various bands, partial density of states (PDOS) and total density of states (TDOS) were deployed. Both compounds are computed by fitting the dispersion relation of the imagined component. Optical properties showed that these compounds were excellent absorbers of incident radiation. Therefore, it may be assumed that these compounds could be employed in magnetic sensors because of anisotropic magnetic behavior and to capture the ultraviolet range of solar radiations.

Empirical band-gap correction for LDA-derived atomic effective pseudopotentials

Atomic effective pseudopotentials enable atomistic calculations at the level of accuracy of density functional theory for semiconductor nanostructures with up to fifty thousand atoms. Since they are directly derived from ab-initio calculations performed in the local density approximation (LDA), they inherit the typical underestimated band gaps and effective masses. We propose an empirical correction based on the modification of the non-local part of the pseudopotential and demonstrate good performance for bulk binary materials (InP, ZnS, HgTe, GaAs) and quantum dots (InP, CdSe, GaAs) with diameters ranging from 1.0 nm to 4.45 nm. Additionally, we provide a simple analytic expression to obtain accurate quasiparticle and optical band gaps for InP, CdSe, and GaAs QDs, from standard LDA calculations.

Unlocking the Magnetic and Half-Metallic Properties of AMY2 (A = Cu, Ag; M = Sc, Ti, V, Cr, Mn, Fe; Y = S, Se) Compounds in Chalcopyrite Structure: An Ab Initio Study for Spintronics Applications

We present an investigation into the magnetism exhibited by AMY2 compounds characterized by a chalcopyrite structure, where A can be Cu or Ag, M can be Sc, Ti, V, Cr, Mn, or Fe, and Y can be either S or Se. By substituting M atoms at the Ga position of AGaY2 compounds, the magnetic properties were calculated using the full potential linearized augmented plane wave method under the generalized gradient approximation and local spin density approximation with the WIEN2K code. The obtained spin-polarized results confirmed the presence of ferromagnetic and half-metallic (HM) properties in AMY2 compounds (A = Cu, Ag; M = Ti, V, Cr, Mn; Y = S, Se), wherein the HM property is preserved through p-d hybridization of p states of Y (S, Se) atoms with d (t2g) states of M (M = Ti, V, Cr, Mn) atoms, and minimal contribution of −s states of A (A = Cu, Ag) atoms. The total magnetic moments for AMY2 compounds were calculated as 1.00, 2.00, 3.00, and 4.00 µB/f.u. for M = Ti, V, Cr, Mn, respectively. For AFeY2 compounds (A = Cu, Ag; Y = S, Se), electronic band structures for both up spin and down spin states were identical, suggesting antiferromagnetic behavior at equilibrium, while AScY2 compounds (A = Cu, Ag; Y = S, Se) exhibited nonmagnetic properties at equilibrium. Overall, the accurate HM properties of AMY2 materials suggest promising prospects for their utilization in spintronics and magnetic storage device applications.

The elastic, electronic, and optical properties of TinO2n-1: Studying of GGA(LDA)+U

Based on the first-principles of density functional theory, the elastic, electronic and optical properties of three titanium suboxides TinO2n-1(n=5，6 and 7) are calculated and analyzed using generalized gradient approximation (GGA+U) and local density approximation (LDA+U) under the pseudopotential of ultra-soft. The results show that all three titanium suboxides are elastically anisotropic, but Ti5O9 has the smallest anisotropy. All the three materials exhibit certain ductility and have certern hardness (∼10 GPa). Electronic structure analysis indicates that Ti5O9, Ti6O11 and Ti7O13 have half-metallic properties, while Ti5O9 also has magnetic property, that is mainly derived from the 3d orbit electrons of Ti atoms. Optical property analysis shows that in the far ultraviolet region (6–12 eV), the reflection coefficient, absorption coefficient and extinction coefficient form resonance.

Superfluid-supersolid phase transition of elongated dipolar Bose-Einstein condensates at finite temperatures

We analyze the finite-temperature phase diagram of a dipolar Bose-Einstein condensate confined in a tubular geometry. The effect of thermal fluctuations is accounted for by means of Bogoliubov theory employing the local density approximation. In the considered geometry, the superfluid-supersolid phase transition can be of first and second order. We discuss how the corresponding transition point is affected by the finite temperature of the system. Published by the American Physical Society 2024

Synthesis, characterization and LDA+U calculations of zinc oxide nanoparticles

Zinc oxide (ZnO) was prepared by the sol-gel method as thin films deposited using spray pyrolysis. The characterization of the synthesized ZnO has been carried out using x-ray diffraction (XRD), Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), and UV-Visible absorption spectroscopy. The experimental results revealed that the prepared ZnO has a wurtzite hexagonal structure with an average crystallite size of about 26.7 nm. High purity and flake-like structures were achieved as SEM and energy dispersive indicated. FTIR confirmed the prepared ZnO’s high purity as the Zn-O stretching peak was very intense. The optical parameters were comprehensively investigated, including absorption, reflection, extinction coefficient, refractive index, and optical energy gap. The wurtzite hexagonal structure of ZnO was optimized using the local-density approximation with the Hubbard correction method (LDA+U). Our experimental result for the energy gap is 3.28 (eV), which is in excellent agreement with the first principle calculations. We utilize the results from the LDA+U calculation along with our experimental outcomes to calculate the thickness of the thin film in UV-Vis spectroscopy.

Non-adiabatic excited-state time-dependent GW molecular dynamics (TDGW) satisfying extended Koopmans' theorem: An accurate description of methane photolysis.

There is a longstanding difficulty that time-dependent density functional theory relying on adiabatic local density approximation is not applicable to the electron dynamics, for example, for an initially excited state, such as in photochemical reactions. To overcome this, we develop non-adiabatic excited-state time-dependent GW molecular dynamics (TDGW) on the basis of the extended quasiparticle theory. Replacing Kohn-Sham orbitals/energies with correlated, interacting quasiparticle orbitals/energies allows the full correspondence to the excited-state surfaces and corresponding total energies, with satisfying extended Koopmans' theorem. We demonstrate the power of TDGW using methane photolysis, CH4→CH3•+H, an important initiation reaction for combustion/pyrolysis and hydrogen production of methane. We successfully explore several possible pathways and show how this reaction dynamics is captured accurately through simultaneously time-tracing all quasiparticle levels. TDGW scales as O(NB3-4), where NB is the number of basis functions, which is distinctly advantageous to performing dynamics using configuration interaction and coupled cluster methods.

Ab initio prediction of half-metallic and metallic ferromagnetism in ZnO:(Co,Cr) systems

Doping effects on the electronic and magnetic properties of Zn1−x (Co,Cr) x O systems are investigated within Local Spin Density Approximation and Hubbard U methods. Based on Density Functional Theory the spin-polarization band structures, density of states for investigated systems are calculated. Systematic analysis of the electronic properties shows that TM-doped ZnO has generated new energy levels in the vicinity of Fermi energy level. From first-principle calculations we obtained Cr-ZnO and Co-ZnO systems are metallic and half-metallic ferromagnetic materials, respectively. The obtained results for Cr-doped ZnO 128- and 192-atom supercell systems show magnetic properties with higher Curie temperature than room temperature. There are large local moments, ∼2.9 and ∼4.2 for Co and Cr dopants, respectively. Magnetic moments are related with two electron defects in the supercell structure and unpaired electrons of transition metal. The ferromagnetic and antiferromagnetic phases and the total energy are obtained for x = 2.08%, 3.125%, 4.16%, 6.25%, 8.3%, 12.5%, and 25% impurity concentrations for doped ZnO.

Comprehensive investigation of half Heusler alloy: Unveiling structural, electronic, magnetic, mechanical, thermodynamic, and transport properties

This study employs density functional theory (DFT) using Wien2k to comprehensively analyze the essential properties of two half-Heusler alloys, KCrSi and KCrGe. Our findings demonstrate that the ferromagnetic Type 2 configuration exhibits superior stability over non-magnetic and antiferromagnetic states for all KCrZ (Z = Si, Ge) alloys. These alloys exhibit complete spin polarization and half-metallic character, with calculated magnetic moments of 3 μB for both KCrSi and KCrGe. The Curie temperature (TC) is determined using the mean field approximation. Mechanical stability is assessed through second-order elastic constants (SOECs), and electronic properties are analyzed using local spin density approximation (LSDA), Perdew-Burke Generalized Gradient Approximation (PBE-GGA), and Tran-Blaha modified Becke-Johnson (TB-mBJ) schemes, confirming the retention of the half-metallic nature. The negative enthalpy of formation (ΔH) suggests material stability. The use of semi-classical Boltzmann theory, incorporated through the sophisticated scheme of BoltzTraP, explores transport coefficients. High pressures and temperature discrepancies in thermodynamics are considered by implementing the quasi-harmonic Debye approximation to illustrate stability. Finally, optical properties are summarized to assess the applicability of this alloy for optoelectronic applications. The overall characteristics of these particular alloys suggest potential applications in sustainable thermoelectric and optoelectronic features.

Orbital-Optimized Versus Time-Dependent Density Functional Calculations of Intramolecular Charge Transfer Excited States.

The performance of time-independent, orbital-optimized calculations of excited states is assessed with respect to charge transfer excitations in organic molecules in comparison to the linear-response time-dependent density functional theory (TD-DFT) approach. A direct optimization method to converge on saddle points of the electronic energy surface is used to carry out calculations with the local density approximation (LDA) and the generalized gradient approximation (GGA) functionals PBE and BLYP for a set of 27 excitations in 15 molecules. The time-independent approach is fully variational and provides a relaxed excited state electron density from which the extent of charge transfer is quantified. The TD-DFT calculations are generally found to provide larger charge transfer distances compared to the orbital-optimized calculations, even when including orbital relaxation effects with the Z-vector method. While the error on the excitation energy relative to theoretical best estimates is found to increase with the extent of charge transfer up to ca. -2 eV for TD-DFT, no correlation is observed for the orbital-optimized approach. The orbital-optimized calculations with the LDA and the GGA functionals provide a mean absolute error of ∼0.7 eV, outperforming TD-DFT with both local and global hybrid functionals for excitations with a long-range charge transfer character. Orbital-optimized calculations with the global hybrid functional B3LYP and the range-separated hybrid functional CAM-B3LYP on a selection of states with short- and long-range charge transfer indicate that inclusion of exact exchange has a small effect on the charge transfer distance, while it significantly improves the excitation energy, with the best-performing functional CAM-B3LYP providing an absolute error typically around 0.15 eV.

Beyond Explored Functionals: A Computational Journey of Two-Photon Absorption.

We present a thorough investigation into the efficacy of 19 density functional theory (DFT) functionals, relative to RI-CC2 results, for computing two-photon absorption (2PA) cross sections (σ2PA) and key dipole moments (|μ00|, |μ11|, |Δμ|, |μ01|) for a series of coumarin dyes in the gas-phase. The functionals include different categories, including local density approximation (LDA), generalized gradient approximation (GGA), hybrid-GGA (H-GGA), range-separated hybrid-GGA (RSH-GGA), meta-GGA (M-GGA), and hybrid M-GGA (HM-GGA), with 14 of them being subjected to analysis for the first time with respect to predicting σ2PA values. Analysis reveals that functionals integrating both short-range (SR) and long-range (LR) corrections, particularly those within the RSH-GGA and HM-GGA classes, outperform the others. Furthermore, the range-separation approach was found more impactful compared to the varying percentages of Hartree-Fock exchange (HF Ex) within different functionals. The functionals traditionally recommended for 2PA do not appear among the top 9 in our study, which is particularly interesting, as these top-performing functionals have not been previously investigated in this context. This list is dominated by M11, QTP variants, ωB97X, ωB97X-V, and M06-2X, surpassing the performance of other functionals, including the commonly used CAM-B3LYP.

The effects of V doping on the intrinsic properties of SmFe10Co2 alloys: A theoretical investigation

The present study focuses on the intrinsic properties of the SmFe10Co2-xVx (x = 0–2) alloys, which includes the SmFe10Co2 alloy, one of the most promising permanent magnets with the ThMn12 type of structure due to its large saturation magnetization (µ0Ms = 1.78 T), high Curie temperature (Tc = 859 K), and anisotropy field (µ0Ha = 12 T) experimentally obtained. Unfortunately, its low coercivity (<0.4 T) hinders its use in permanent magnet applications. The effect of V-doping on magnetization, magnetocrystalline anisotropy energy, and Curie temperature is investigated by electronic band structure calculations. The spin-polarized fully relativistic Korringa-Kohn-Rostoker (SPR-KKR) band structure method, which employs the coherent potential approximation (CPA) to deal with substitutional disorder, has been used. The Hubbard-U correction to local spin density approximation (LSDA + U) was used to account for the large correlation effects due to the 4f electronic states of Sm. The computed magnetic moments and magnetocrystalline anisotropy energies were compared with existing experimental data to validate the theoretical approach’s reliability. The exchange-coupling parameters from the Heisenberg model were used for obtaining the mean-field estimated Curie temperature. The magnetic anisotropy energy was separated into contributions from transition metals and Sm, and its relationships with the local environment, interatomic distances, and valence electron delocalization were analyzed. The suitability of the hypothetical SmFe10CoV alloy for permanent magnet manufacture was assessed using the calculated anisotropy field, magnetic hardness, and intrinsic magnetic properties.

A mathematical analysis of the adiabatic Dyson equation from time-dependent density functional theory

In this article, we analyse the Dyson equation for the density–density response function (DDRF) that plays a central role in linear response time-dependent density functional theory (LR-TDDFT). First, we present a functional analytic setting that allows for a unified treatment of the Dyson equation with general adiabatic approximations for discrete (finite and infinite) and continuum systems. In this setting, we derive a representation formula for the solution of the Dyson equation in terms of an operator version of the Casida matrix. While the Casida matrix is well-known in the physics literature, its general formulation as an (unbounded) operator in the N-body wavefunction space appears to be new. Moreover, we derive several consequences of the solution formula obtained here; in particular, we discuss the stability of the solution and characterise the maximal meromorphic extension of its Fourier transform. We then show that for adiabatic approximations satisfying a suitable compactness condition, the maximal domains of meromorphic continuation of the initial DDRF and the solution of the Dyson equation are the same. The results derived here apply to widely used adiabatic approximations such as (but not limited to) the random phase approximation and the adiabatic local density approximation. In particular, these results show that neither of these approximations can shift the ionisation threshold of the Kohn–Sham system.

Effect of XC functionals and dispersion corrections on the DFT‐computed structural and vibrational properties of SrCl2–NaCl and ZrF4–LiF

AbstractDensity functional theory (DFT) calculations were performed to examine the impact of exchange–correlation (XC) functionals and van der Waals corrections (specifically the D3 method) on the structural and vibrational properties of the SrCl2–NaCl and ZrF4–LiF salt systems. Multiple XC functionals, including the local density approximation (LDA), the generalized gradient approximation using the Perdew–Burke–Ernzerhof (PBE) model, and its modified form suitable for solids (PBEsol), the dispersion‐corrected PBE‐D3 and PBEsol‐D3, were considered. Of these functionals, LDA was found to exhibit the highest degree of error, while PBEsol and PBE‐D3 displayed the least error. Underestimated lattice parameters compared with experimental values were observed to result in higher force constants, leading to an overprediction of vibrational frequencies. Conversely, an overestimation of lattice parameters was associated with lower vibrational frequencies. The methodology presented in this study yielded results that are in good agreement with experiment, irrespective of the method (finite differences vs. density functional perturbation theory) employed for calculating infrared and Raman spectra. It was further demonstrated that for alkali halides with weak Raman scattering, utilizing a supercell constructed from primitive cells better predicts Raman features than does the use of conventional cells.

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.

Study of the Phase Transition and Physical Properties of AlAs, ScAs and AlxSc1-XAs Compounds by the FP-LMTO Method

Abstract In this present work, we will study the physical properties of a brand new semiconductor material. the structural stability and the electronic properties of Scandium Arsenide (ScAs) and Aluminum Arsenide (AlAs) semiconductors as well as their ternary alloys (AlxSc1-xAs, 0≤ x≤1) in both rocksalt RS (B1) and zincblende ZB (B3). Calculations on both structures are done the method (FPLMTO, Full Potential Linear Muffin Tin). In the framework of density functional theory (DFT). The exchange-correlation potential was calculated using both the Local Density Approximation and the Generalized Gradient Approximation. The structural parameters of AlxSc1-xAs alloys, such as the lattice constant, the bulk module and its derivative are calculated. The lattice parameter deviates slightly from the line of Vegard’s Law in B3 structure, while the deviation was more pronounced in B1 structure. The calculations showed a phase transition from the ZnS phase (B3) to the RS phase (B1) at pressures (7, 10.5, 14.0 and 23.0 Gpa in LDA and (10.0, 12.5, 10.0 and 25.0 GPa) in GGA for x = 0.25, 0.50, 0.75 and 1.00) respectively.The calculated electronic properties showed that in phase B1, there exists an energy band (X-X) with a direct gap at x = 0.00. On the other hand, in phase B3, there are two kinds of energy bands, of direct gap (Γ-Γ) for x = 0.25, 075 and 1.00, the second band is of indirect gap (Γ-X) for x = 0.50, suggesting the possibility to be used in the long wavelength optoelectronic applications. The deviation of The calculated band gap deviation from linear behavior was significant in both structures. The AlxSc1-xAs alloys were found to be semiconducting at x=0 in the B1 phase and at x=0.25, 0.50, 0.75 and 1 in the B3 phase. Concerning calculations of the optical properties of the ternary AlxSc1-xAs alloy at concentrations x= 0.25, 0.50 and 0.75 in the ZnS (B3) phase, and from our bibliographic research we are sure that no reference exists in the literature. Our work can therefore be used as a reference for future research. Our simulation results are in good agreement with those obtained theoretically and experimentally.

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.

A DFT+U Study of the Structural and Electronic Properties of Zinc Doped Anatase TiO2 Nanomaterial

This work reports a theoretical study on the structural and electronic properties of the anatase phase of titanium dioxide (TiO2) within the framework of density functional theory corrected for on-site coulomb interactions in strongly correlated materials (DFT+U). The exchange correlation was described by local density approximation (LDA). The optimized lattice parameters obtained for the pure anatase TiO2 agree with the experimental data. Our results revealed that, after the zinc doping, the structure didn't change but there was a little expansion in the volume of the pure material. It was found that the doped structure's stability increases as the concentration of the dopant increases, but all the doped structures are stable. However, introducing the zinc dopant has significantly reduced the band gap of the pure anatase by 80.7 %, 80 %, and 78.6 % due to 0.25, 0.5, and 0.75 doping concentrations, respectively. This implies that the band gap energy increases as the doping concentration increases.

Ab initio investigation of mechanical, electronic and optical properties in the orthorhombic [formula omitted] inorganic perovskite

This study employs a first-principles approach to comprehensively investigate the structural, electronic, elastic, and optical properties of two distinct inorganic perovskite phases of CsPbI3, identified as C–CsPbI3 and O–CsPbI3. Utilizing the Wien2K code, simulations are conducted employing various density functional theory (DFT) approximations, including local density approximation (LDA), generalized gradient approximation (GGA), the modified Becke–Johnson potential (mBJ), and the Tran-Blaha modified Becke–Johnson potential (TB-mBJ). Our analysis demonstrates that the orthorhombic phase exhibits greater energetic stability and mechanical robustness compared to the cubic phase. Furthermore, optical analyses reveal a direct bandgap in the compound, with key parameters calculated and interpreted. Notably, both phases demonstrate exceptional electronic, mechanical, and optical properties, suggesting their potential applications in optoelectronics, photovoltaics, and photovoltaic cells. Consequently, this study positions both the cubic and orthorhombic phases of CsPbI3 as promising materials warranting further exploration and development in these technological domains.

DFT-1/2 for ionic insulators: Impact of self-energy potential on band gap correction

DFT-1/2 is an efficient band gap correction method for density functional theory under local density approximation or generalized gradient approximation. Nevertheless, it still predicts lower band gaps than experimental in highly ionic insulators, such as LiF and CsCl. In this study, we emphasize that the problem is more severe for halides. For example, the DFT-1/2 band gap for Li2O is much more satisfactory than that for LiF. Notwithstanding the traditional belief that high ionicity is the key, we ascribe the main reason to the fact that the self-energy potentials (SEPs) used for anions were derived based on neutral atoms. Extensive tests have shown that an SEP derived from an atom/ion with fewer electrons is stronger than that derived with more electrons. The degree of enhancement in the O SEP, based on O rather than O2–, could generally compensate for the loss of SEP in the trimming process. In the case of halides, such compensation is insufficient, resulting in small band gaps. For ionic nitrides involving N3–, the SEP is undesirably large if it is derived from a neutral N atom. Equivalent scaling factors are prescribed for the SEPs of F and N, with the former being greater and the latter being smaller than unity. With proper SEP scaling factors according to the charge carried by the anion, the DFT-1/2 band gaps are greatly improved for highly ionic insulators.