Self-interaction-corrected Local Density Approximation Research Articles

Co-, Fe-, Ni-doped and co-doped rutile GeO2: insights from ab-initio calculations

Abstract Rutile germanium oxide (rutile GeO2), a semiconductor, can act as a half-metallic compound and is a promising material for spintronic and optoelectronic applications. Calculations were performed using the Korringa–Kohn–Rostoker (KKR) approach and the coherent potential approximation (CPA), which were further combined with two approximations, the local density approximation (LDA) and the self-interaction corrected LDA approximation (LDA-SIC), to study the electronic structure of bulk rutile GeO2 doped and co-doped with three transition-metal impurities: Fe, Co, and Ni. The doping value was set to 10%, while the co-doping level was set to 5% for each impurity. The main findings of this work are: (1) a direct ultrawide bandgap of 4.80 eV is observed and the rutile GeO2 exhibits an N-type semiconducting property. (2) Doped and co-doped GeO2 acquire a magnetic behavior and exhibit half-metallicity. (3) The mechanism responsible for these properties is also studied. (4) The critical temperature can reach 334 K when GeO2 is doped with Fe, while it rises to 398 K when it is co-doped with Fe and Co. (5) The spin polarization can be improved by co-doping. It can be inferred that rutile GeO2 doped or co-doped with (Co, Fe) transition metals can be considered to be potential candidates for spintronic and optoelectronic applications.

The electronic, magnetic and optical properties of ZnO doped with doubles impurities (Cr, Fe): An LDA-SIC and Monte Carlo study

Electronic structure, magnetic and optical properties of ZnO doped with single and double impurities Zn1−xCrxO, Zn1−xFexO, and Zn1−2xCrxFexO (x=0.03 and 0.06) are investigated using first-principles calculations. Based on the Korringa–Kohn–Rostoker method combined with the coherent potential approximation, we investigated the half-metallic ferromagnetic behavior of doubles impurities (Cr, Fe) doped ZnO. To support our results, we apply the self-interaction-corrected local density approximation (SIC-LDA) to study the electronic structure, optical and magnetic properties of Co-doped ZnO with doubles impurities (Cr, Fe) showing that the half-metallic ferromagnetic state still persists. The stability of the ferromagnetic state compared with the spin-glass state is investigated by comparing their total energies. The exchange interactions obtained from first principle calculations and used in a classical Ising model by a Monte Carlo approach resulted in ferromagnetic states with high Neel temperature.

Half-Metallic Behavior of Transition Metal-Doped Chalcopyrite Semiconductor: LDA and SIC-LDA Calculation

Using the first principles with local density approximation (LDA) and self-interaction-corrected local density approximation (SIC-LDA), the electronic structure of transition metal-doped copper indium sulfide chalcopyrite (CuInS2) has been calculated and the effect of low-impurity concentration on magnetic structure has been carried out for both LDA and SIC-LDA; also, the magnetic transition temperature for Cr-doped CuInS2 was reported in the concentration range of 1–6 % with LDA and SIC-LDA. It is shown that the chalcopyrite semiconductor-doped transition metals (with low concentration) exhibit a high magnetic critical temperature and half-metallic behavior that could have a significant participation in spintronic applications.

Low-energy phases, electronic and optical properties of Bi1−xLaxFeO3 solid solution: Ab-initio LDA+U studies

Modification of BiFeO3 by substituting Bi (III) with La (III) was studied using ab-initio method based on self-interaction corrected local density approximation plus Hubbard-like U approach, as implemented in plane-wave pseudopotential Cambridge Serial Total Energy Package code. Possible stable phases of BiFeO3 and Bi1−xLaxFeO3 were determined from the calculated total energy. Phase transformation of rhombohedral to orthorhombic in Bi1−xLaxFeO3 solid solution occurred at 0.57 La concentration ratio for rhombohedral R3c and orthorhombic Pn21a phases, consistent with the available experimental and other calculation studies. The electronic band structure, density of states, and optical properties of Bi1−xLaxFeO3 were also investigated. Results showed that the electronic and optical properties of Bi1−xLaxFeO3 were mainly influenced by La concentration, but slightly affected by structural phase transformation. These results would provide a theoretical reference for fundamental science and technological application of Bi1−xLaxFeO3 solid solution.

The Transition Metal Doped ZnO: The Self-interaction Corrected LSDA Calculation

Electronic structures of ZnO-based dilute magnetic semiconductors (DMS) are investigated within the self-interaction-corrected local density approximation (SIC-LDA). These results are compared with those calculated within the standard LDA. The Korringa–Kohn–Rostoker method combined with coherent potential approximation has been used. We find the differences between LDA and SIC-LDA calculations, in the band-gap energy. The energetic position of the Zn 3d bands and the description of the transition-metal d bands, have been studied. In contrast to the standard LDA calculations, the results obtained within SIC-LDA are in good agreement with the experimental ones.

Materials design of CuIn1−xZn0.5xSn0.5xSe2 for low cost photovoltaic solar cells

Computational material design of a strategy for resource security of chalcopyrite-based photovoltaic solar cells (PVSC) is investigated. The electronic structure of CuIn1−xZn0.5xSn0.5xSe2 (CIZTS) is calculated by using the self-interaction-corrected local density approximation (SIC-LDA) and the Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA). It is shown that for any degree of substitution for In, CIZTS has a direct band gap and no impurity state is induced in the band gap. We propose a possibility of substitutional co-doping of Zn and Sn for In in CuInSe2 photovoltaic material to reduce the cost of materials for PVSC production.

First-principles materials design of CuInSe2-based high-efficiency photovoltaic solar cells

Based on ab initio electronic structure calculations by self-interaction-corrected local-density-approximation (SIC-LDA) with the Korringa–Kohn–Rostoker coherent potential approximation (KKR-CPA), we propose a materials design for high efficiency photovoltaic solar cells (PVSCs). It is shown that (i) the concentration dependence of the mixing energy of CuIn1−xGaxSe2 shows upward convexity, thus this system favors phase separation. Due to the type II band alignment between CuInSe2 and CuGaSe2, efficient electron–hole separation is realized in decomposed phase of this system. (ii) CuIn1−xZn0.5xSn0.5xSe2 has a direct band gap and no impurity state appears in the gap. Therefore, cost reduction is possible by using Zn and Sn instead of In. (iii) n-type CuAl1−xSnxS2 and p-type Cu1−xVCuxAlS2 have negative activation energy for doped impurities and are expected to be low-resistive transparent conducting sulfides, which should be useful for CuInSe2-based PVSCs.

First-principles calculations of electronic structure on (Ti,Co)O 2 within self-interaction-corrected LDA

Electronic structure of TiO 2 (rutile) based dilute magnetic semiconductors (DMS) are investigated within self-interaction-corrected local density approximation (SIC-LDA) from first-principles calculation. These results are compared with those calculated within standard LDA. It is found that the calculated band-gap energy in the host TiO 2 is different within the LDA and the SIC-LDA. We find that high-spin state is predicted within the SIC-LDA with oxygen vacancy. The calculated density of states within SIC-LDA is in good agreement with photoemission results.

Self-interaction correction with Wannier functions

We describe the behavior of the Perdew-Zunger self-interaction-corrected local density approximation (SIC-LDA) functional when implemented in a plane-wave pseudopotential formalism with Wannier functions. Prototypical semiconductors and wide-bandgap oxides show a large overcorrection of the LDA bandgap. Application to transition-metal oxides and elements with d electrons is hindered by a serious breaking of the spherical symmetry, which appears even in a closed shell free atom. Our results indicate that, when all spherical approximations are lifted, the general applicability of orbital-dependent potentials is very limited and should be reconsidered in favor of rotationally invariant functionals.

Momentum-space properties of atoms: Application of the generalized-gradient approximation

The calculations of Compton profiles and various $〈{p}^{n}〉$-expectation values are carried out for a few closed-shell atomic systems within Perdew-Burke-Ernzerhof (PBE), Perdew-Wang 1991 (PW91) and Becke-Lee-Yang-Parr (BLYP) generalized-gradient approximations. The calculated Compton profiles and the moments are compared with their local-density approximation (LDA) and more accurate available theoretical or experimental counterparts in order to investigate the supremacy of generalized gradient approximation (GGA) over LDA in predicting the momentum-space properties. The results show that GGA improves the Compton profiles marginally. The PBE and PW91 values of Compton profiles are practically identical and are slightly better than BLYP. Further comparison of GGA and LDA results with those calculated within self-interaction corrected LDA (SICLDA) formalism demonstrates the importance of proper description of the valence region in the study of Compton profiles. GGA values of the moments of electron momentum density are found to be, in general, more accurate than their LDA counterparts.

Excitation energies from time-dependent density functional theory using exact and approximate potentials

The role of the exchange–correlation potential and the exchange–correlation kernel in the calculation of excitation energies from time-dependent density functional theory is studied. Excitation energies of the helium and beryllium atoms are calculated, both from the exact Kohn–Sham ground-state potential and from two orbital-dependent approximations. These are exact exchange and self-interaction corrected local density approximation (SIC-LDA), both calculated using Krieger–Li–Iafrate approximation. For the exchange–correlation kernels, three adiabatic approximations were tested: the local density approximation, exact exchange, and SIC-LDA. The choice of the ground-state exchange–correlation potential has the largest impact on the absolute position of most excitation energies. In particular, orbital-dependent approximate potentials result in a uniform shift of the transition energies to the Rydberg states. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 534–554, 2000

Simple method for constructing accurate atomic Kohn-Sham potentials

Recently, a great deal of attention has been devoted to the near-exact Kohn-Sham (KS) atomic potentials, mainly obtained from quantum Monte Carlo (QMC) calculations for a few significant test cases. We show that the potential of the highest occupied orbital in the self-interaction corrected local-density approximation (SIC-LDA) approach provides an excellent approximation for the QMC potentials, far better than the commonly used ones. Moreover, near-exact KS potentials of the same quality as the QMC ones can be obtained from the SIC-LDA potentials of the highest occupied and lowest empty orbitals, by a simple two-parameter fitting procedure to reproduce the experimental values of the ionization and first excitation energies. This has been demonstrated by a quantum-defect analysis of the empty states of Ne and Be atoms, for which QMC potentials are available to us. The introduced method is used to construct a near-exact KS potential for Ar.

Theory of theα−γphase transition in Ce

The Kondo volume collapse model of the isostructural $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\gamma}$ phase transition in elemental cerium is investigated by a combination of the self-interaction-corrected local-density approximation (SIC-LDA) and the Anderson impurity model. The zero-temperature uncorrelated total-energy function as well as the model hybridization parameters are calculated with the SIC-LDA approach, while temperature and correlation effects are calculated within the impurity model, using an extension of the noncrossing approximation. It is found that the phase transition may be quantitatively well described with this approach, provided a rescaling of the hybridization parameters is invoked. The influence of Ce ${f}^{2}$ configurations on the accuracy of the calculations is discussed.

Critical assessment of the self-interaction-corrected–local-density-functional method and its algorithmic implementation

We calculate the electronic structure of several atoms and small molecules by direct minimization of the Self-Interaction Corrected Local Density Approximation (SIC-LDA) functional. To do this we first derive an expression for the gradient of this functional under the constraint that the orbitals be orthogonal and show that previously given expressions do not correctly incorporate this constraint. In our atomic calculations the SIC-LDA yields total energies, ionization energies and charge densities that are superior to results obtained with the Local Density Approximation (LDA). However, for molecules SIC-LDA gives bond lengths and reaction energies that are inferior to those obtained from LDA. The nonlocal BLYP functional, which we include as a representative GGA functional, outperforms both LDA and SIC-LDA for all ground state properties we considered.

Theoretical investigation of the polarizability of small metal clusters

In this paper we study the polarizabilities of small metal clusters within exchange-only (XO) employing the spherical jellium model. We explain the similarity of results between the XO local-density approximation (LDA) and other exact/near exact XO theories in terms of the effective potential seen by the electrons in these theories. Furthermore we show that unlike the fully-correlated case, the self-interaction corrected LDA leads to polarizabilities which are close to the LDA results. We discuss within XO the implications of this for the fully-correlated case.

X-ray absorption of transition metal oxides: An overview of the theoretical approaches

A short overview is given of the different approaches to interpreting X-ray absorption spectroscopy (XAS), and particularly their relation to electronic structure models. The electronic structure models which incorporate many-electron effects, such as GW calculations, the Hubbard model and self-interaction corrected local density approximation (LDA) calculations, are outlined. Special attention is given to the use of Hubbard model for core level spectroscopies. Within this background two extreme models for interpreting X-ray absorption spectra are discussed in detail: the ligand field multiplet model to interpret metal 2p-XAS spectra and LDA calculations to interpret oxygen 1s-XAS spectra. Finally the open problem of possible final state effects on model hamiltonians is outlined.