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1.
2.
The electronic structure and ferromagnetic stability of Co-doped SnO2 are studied using the first-principle density functional method within the generalized gradient approximation (GGA) and GGA+U schemes. The addition of effective UCo transforms the ground state of Co-doped SnO2 to insulating from half-metallic and the coupling between the nearest neighbor Co spins to weak antimagnetic from strong ferromagnetic. GGA+UCo calculations show that the pure substitutional Co defects in SnO2 cannot induce the ferromagnetism. Oxygen vacancies tend to locate near Co atoms. Their presence increases the magnetic moment of Co and induces the ferromagnetic coupling between two Co spins with large Co-Co distance. The calculated density of state and spin density distribution calculated by GGA+UCo show that the long-range ferromagnetic coupling between two Co spins is mediated by spin-split impurity band induced by oxygen vacancies. More charge transfer from impurity to Co-3d states and larger spin split of Co-3d and impurity states induced by the addition of UCo enhance the ferromagnetic stability of the system with oxygen vacancies. By applying a Coulomb UO on O 2 s orbital, the band gap is corrected for all calculations and the conclusions derived from GGA+UCo calculations are not changed by the correction of band gap.  相似文献   

3.
The electronic and magnetic properties of NdCrSb3 are calculated by the first principles full-potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). Density of states (DOS), magnetic moments and band structures of the system are presented. For the exchange and correlation energy, local spin density approximation (LSDA+U) with the inclusion of Hubbard potential U is used. Our calculation shows that the 3d state electron of Cr and 4f state electrons of Nd contribute to the total DOS and the band structures. The effective magnetic moment is found to be 5.77μB, which is comparable to the earlier experimental results of NdCrSb3.  相似文献   

4.
We have calculated the on-site Coulomb repulsion (U) for the transition elements Co and Fe. To study the impact of Hubbard potential or on-site Coulomb repulsion (U) on structural and electronic properties the calculated values of U were added on GGA and LSDA. We performed the structure optimization of Co2FeGe based on the generalized gradient approximation (GGA and GGA+U). The calculation of electronic structure was based on the full potential linear augmented plane wave (FP-LAPW) method and local spin density approximation (LSDA) as well as exchange correlation LSDA+U. The Heusler alloy Co2FeGe fails to give the half-metallic ferromagnetism (HMF) when treated with LSDA. The LSDA+U gives a good result to prove that Co2FeGe is a HMF with a large gap of 1.10 eV and the Fermi energy (EF) lies at the middle of the gap of minority spin. The calculated density of states (DOS) and band structure show that Co2FeGe is a HMF when treated with LSDA+U.  相似文献   

5.
First-principles calculations, by means of the full-potential augmented plane wave method using the LSDA+U approach (local spin density approximation with Hubbard-U corrections), have been carried out for the electronic structure of the Al0.75Er0.25N. The LSDA+U method is applied to the rare-earth 4? states. We have investigated the electronic and magnetic properties.The Al0.75Er0.25N is shown to be a semiconductor, where the filled ? states are located in the valence bands and the empty ones above the conduction band edge. The magnetic interaction of the rare-earth ion with the host states at the valence and conduction band edges has been investigated and discussed.  相似文献   

6.
First-principles density functional theory calculations have been carried out to investigate electronic structures of anatase TiO2 with substitutional dopants of N, Nd, and vacancy, which replace O, Ti, and O, respectively. The calculation on N-doped TiO2 with the local density approximation (LDA) demonstrates that N doping introduces some states located at the valence band maximum and thus makes the original band gap of TiO2 smaller. Examining the effect of the strong correlation of Nd 4f electrons on the electronic structure of Nd-doped TiO2, we have obtained the half-metallic ground state with the LDA and the insulating ground state with the LDA+U (Hubbard coefficient), respectively. In addition, the calculation on vacancy-doped TiO2 with the LDA shows that a vacancy can induce some states in the band-gap region, which act as shallow donors.  相似文献   

7.
We report a comparative study of the electronic structure and magnetic properties of two cobalt compounds Co3O4 and Co3S4, through first-principles Hubbard-U calculations. Our results indicate that Co3O4 and Co3S4 have similarities in crystal structure (normal spinel), magnetic order (antiferromagnetism), Co spin configuration (high spin Co2+ and low spin Co3+), and comparable band-gap energy. However, the U-dependence on electronic structure in two materials are different from each other. With a change in the applied U values, the band dispersion and the type of band gap are significantly changed in Co3O4, while the band-gap energy only is affected in Co3S4.  相似文献   

8.
Structure and physical properties of BiF3 doped with M=Cr, Cu, Fe, Mn, Ni, Ti, V and Co are calculated by the DFT+U method. Effect of metal doping on the electronic structure and optical response of host materials BiF3 is investigated systematically. New energy levels are formed and located within the band gap, which could decrease the recombination rate of e/h+ pairs. Furthermore, transition metal doping extends the optical absorption of BiF3 to the visible spectral region.  相似文献   

9.
The 3d transition metal binary compounds have been extensively investigated for a large multi-electron redox capacity through reversible electrochemical reactions. Here, the structural, electronic and magnetic properties of CuF2 are studied by the first-principles calculations within both the generalized gradient approximation (GGA) and GGA+U frameworks. Our results show that the antiferromagnetic (AFM) configuration of CuF2 is more stable than the ferromagnetic (FM) one, which is consistent with experiments. The analysis of the electronic density of states (DOS) shows that CuF2 is a classic Mott–Hubbard insulator with a large dd type band gap, which is similar to the case of FeF3. Moreover, small spin polarizations were found on the sites of fluorin ions, which accords with a fluorin-mediated superexchange mechanism for the Cu–Cu magnetic interaction.  相似文献   

10.
Electronic structure calculations based on density functional theory (DFT) within the generalized gradient approximation (GGA) and GGA+U for manganite cuprate compound LuCu3Mn4O12 have been performed, using the full-potential linearized augmented plane wave method. The calculated results indicate that LuCu3Mn4O12 is ferrimagnetic and half-metallic in both GGA and GGA+U calculations. The minority-spin band gap is 0.7 eV within GGA, which is larger than that of LaCu3Mn4O12 (0.3 eV), indicating its better half-metallicity. Further, the minority-spin gap enlarges from 0.7 to 2.8 eV with U taken into account, and simultaneously the Fermi level being shifted to the middle of the gap, making the half-metallic energy gap to be 1.21 eV. These results demonstrate that electronic correlation effect enhances the stability of half-metallic property. These facts make this system interesting candidates for applications in spintronic devices.  相似文献   

11.
Comparative GGA and GGA+U calculations for pure and Mo doped anatase TiO2 are performed based on first principle theory, whose results show that GGA+U calculation provide more reliable results as compared to the experimental findings. The direct band gap nature of the anatase TiO2 is confirmed, both by using GGA and GGA+U calculations. Mo doping in anatase TiO2 narrows the band gap of TiO2 by introducing Mo 4d states below the conduction band minimum. Significant reduction of the band gap of anatase TiO2 is found with increasing Mo doping concentration due to the introduction of widely distributed Mo 4d states below the conduction band minimum. The increase in the width of the conduction band with increasing doping concentration shows enhancement in the conductivity which may be helpful in increasing electron–hole pairs separation and consequently decreases the carrier recombination. The Mo doped anatase TiO2 exhibits the n-type characteristic due to the shifting of Fermi level from the top of the valence band to the bottom of the conduction band. Furthermore, a shift in the absorption edge towards visible light region is apparent from the absorption spectrum which will enhance its photocatalytic activity. All the doped models have depicted visible light absorption and the absorption peaks shift towards higher energies in the visible region with increasing doping concentration. Our results describe the way to tailor the band gap of anatase TiO2 by changing Mo doping concentration. The Mo doped anatase TiO2 will be a very useful photocatalyst with enhanced visible light photocatalytic activity.  相似文献   

12.
The effects of mono-doping of 4f lanthanides with and without oxygen vacancy defect on the electronic structures of anatase TiO2 have been studied by first-principles calculations with DFT+U (DFT with Hubbard U correction) to treat the strong correlation of Ti 3d electrons and lanthanides 4f electrons. Our results revealed that dopant Ce is easy to incorporate into the TiO2 host by substituting Ti due to its lower substitutional energy (∼−2.0 eV), but the band gap of the system almost keeps intact after doping. The Ce 4f states are located at the bottom of conduction band, which mainly originates from Ti 3d states. The magnetic moment of doped Ce disappears due to electron transfer from Ce to the nearest O atoms. For Pr and Gd doping, their substitutional energies are similar and close to zero, indicating that both of them may also incorporate into the TiO2 host. For Pr doping, some 4f spin-down states are located next to the bottom of the conduction band and narrow the band gap of the doping system. However, for Gd doping, the 4f states are located in deep valence band and there is no intermediate band in the band gap. The magnetic moment of dopant Gd is close to the value of isolated Gd atom (∼7 μB), indicating no overlapping between Gd 4f with other orbitals. For Eu, it is hard to incorporate into the TiO2 host due to its very higher substitutional energy. The results also indicated that oxygen vacancy defect may enhance the adsorption of the visible light in Ln-doped TiO2 system.  相似文献   

13.
Lin Zhu  Taimin Cheng 《Physics letters. A》2010,374(29):2972-2979
Generalized gradient approximation (GGA) and GGA + U (U denotes on-site Coulomb interactions) methods are applied to investigate the magnetic and electronic structures of the perovskite oxide Nd2/3Sr1/3MnO3. Under GGA the compound prefers ferrimagnetic ordering in which Nd sublattice is spin-antiparallel to Mn sublattice. Nd 4f states cross over the Fermi level under GGA, leading the ferrimagnetic Nd2/3Sr1/3MnO3 to a metallic character. The on-site Coulomb interactions should be included to emphasize the localized feature of Nd 4f states. Under GGA + U, the spins of Nd and Mn sublattices tend to be parallel in the ground state, and fully spin-polarized Mn 3d electrons yield a half-metallic band structure for the ferromagnetic Nd2/3Sr1/3MnO3. The ferromagnetic coupling between Nd and Mn sublattices is ascribed to the super-exchange interaction between Nd 4f and Mn 3d (t2g) electrons via O 2p electrons.  相似文献   

14.
The electronic and magnetic structures of ordered double perovskites Ba2TMoO6 (T=V, Cr, Mn, Fe and Co) are systematically investigated by means of the first-principle linear muffin-tin orbitals with the atomic-sphere approximation (LMTO-ASA) method. The calculations are performed by using the both local spin density approximation (LSDA) and the LSDA+U Coulomb interaction schemes. The results show a half-metallic ferrimagnetic ground states for T=Cr, Fe and Co in LSDA+U treatment, whereas half-metallic ferromagnetic character is observed for T=V. For T=Mn, insulating ground state is obtained, stabilized in the antiferromagnetic state. The LSDA+U calculations yield better agreement with the theoretical and the experimental results than do the LSDA.  相似文献   

15.
The ground-state properties of NiO have been investigated using the all-electron full-potential linearized augmented plane wave (FLAPW) and the so-called LSDA (GGA)+U (LSDA—local-spin-density approximation; GGA—generalized gradient approximation) method. The calculated result indicates that our estimation of U is in good agreement with experimental data. It is also found that none of the LSDA (GGA) methods is able to provide, at the same time, accurate electronic and structural properties of NiO. Although the GGA+U method can properly predict the electronic band gap, it overestimates the lattice constant and underestimates the bulk modulus. Then only the LSDA+U method accurately reports the electronic and structural properties of NiO. The calculated band gap and the density of states (DOS) show that the material NiO is the charge-transfer insulator, which agrees with the spectroscopy data. The comparison between the charge density of LSDA (not considering U) and that of LSDA+U (considering U) demonstrates that the trend of ionic crystal for NiO is obvious.  相似文献   

16.
The band gap of LaCoO3 in ground state is obtained from the generalized gradient approximation (GGA) with on-site Coulomb correction (GGA+U) calculations (U=3.4 eV, J=0.49 eV ), which agrees with the experimental result very well. A series of local spin density approximation (LSDA) with on-site Coulomb corrections (LSDA+U) and GGA+U calculations are performed with various U and J parameters to understand the recently published band gaps of 1.43 eV from LSDA+U (U=8.33 eV ) and 1.0 eV from GGA+U (U=2.7) calculations. The partial density of states (PDOSs) are presented to investigate the origin of the band gap.  相似文献   

17.
The crystal structure, magnetic and electronic properties of SmFeO3 under hydrostatic pressure have been studied by first-principles calculations within the generalized gradient approximation plus Hubbard U (GGA + U). The iso-structural phase transition with spin, volume and band gap collapses can be induced by a large enough hydrostatic pressure. The high-spin (HS) state of Fe3+, with the magnetic moment of ~4 μB, is retained at low pressure. The spin crossover occurs at a transition pressure (~68 GPa) with the magnetic moment of Fe3+ decreasing to ~1 μB in low-spin (LS) state. Meanwhile, the reductions of cell volume (by ~?5.43%) and band gap (from >2 eV to ~1.6 eV) of SmFeO3 are obtained when the HS–LS transition happens. Finally, the critical pressure of HS–LS transition, magnetic and electronic properties are found to be Hubbard U dependent.  相似文献   

18.
This study investigates the optical properties of selected metal oxides due to their high dielectric constants. The local-spin-density approximation plus Hubbard U (commonly called LDA+U) is used in a study of the structural, mechanical and optical properties of UO2. The inclusion of a Hubbard U correction to 5f electrons of uranium changes UO2 from a metal to an insulator and, therefore, has a dramatic effect on the localisation of the electron spin and charge density of uranium. However although the band gap can be reproduced using the effective U parameter, which is equal to 3.5 eV and optical properties were calculated in our previous work, it is difficult to calculate ionic contribution to the static dielectric constant within LDA+U formalism for this compound. It is shown in the present work that the electronic structures of both ceria and thoria exhibit similarities to urania within LDA or PBE functional implementations. Within this functional and linear response theory one can easily calculate static dielectric permittivity and it is shown that in agreement with experiment the predicted values are an order of magnitude larger than the dielectric constant of SiO2. In this work, high accuracy, first-principles calculations are also used to compare properties of urania versus ceria and thoria and how these similarities can help in understanding these compounds. It is also shown that the B3LYP functional predicts slightly overestimated band gaps for ceria and thoria as well as smaller than experimentally observed electronic contribution to the static dielectric constant, while the index of refraction is well reproduced for thoria.  相似文献   

19.
We preformed first-principle calculations for the structural, electronic, elastic and magnetic properties of Cu2GdIn, Ag2GdIn and Au2GdIn using the full-potential linearized augmented plane wave (FP-LAPW) scheme within the generalized gradient approximation by Wu and Cohen (GGA-WC), GGA+U, the local spin density approximation (LSDA) and LSDA+U. The lattice parameters, the bulk modulus and its pressure derivative and the elastic constants were determined. Also, we present the band structures and the densities of states. The electronic structures of the ferromagnetic configuration for Heusler compounds (X2GdIn) have a metallic character. The magnetic moments were mostly contributed by the rare-earth Gd 4f ion.  相似文献   

20.
Particularly interesting as candidates to technological applications are the manganese perovskites with AMnO3 formula. Their magnetic structure was described as resulting from a particular ordering of the occupied d orbitals which possess. This reflects my understanding of the structural, electronic and magnetic phenomena, which is well established only in the limit where the systems show localized or itinerant electron behavior. In general, the perovskites of ABO3-type are well known with their (anti)ferroelectric, piezoelectric and (anti)ferromagnetism properties applied in considerable technological investigations. In my paper, I studied the ground states properties of the BaMnO3 perovskite oxide. My structural properties are given using LSDA, GGA, LSDA+U and GGA+U in the aim to introduce the exchange correlation potential. In the following paper, I use the GGA+U on the electronic and magnetic properties calculation. I show in my study the density of states, the band structures and also the charge density figures. My results such as lattice parameter, bulk modulus and its pressure derivative agree very well with available theoretical works and experimental data. I discuss the magnetic moment and the U-Hubbard effect introduced by LSDA+U and GGA+U on my results given in this paper.  相似文献   

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