Electron correlation effects in small iron clusters

2004 ◽  
Vol 1 (4) ◽  
pp. 288-296 ◽  
Author(s):  
G. Rollmann ◽  
P. Entel
Keyword(s):  
Electron Correlation ◽  
Density Functional ◽  
Magnetic Moments ◽  
Coulomb Repulsion ◽  
Correlation Effects ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Jahn Teller ◽  
Electron Correlation Effects ◽  
Ground State Structures

We present results of first-principles calculations of structural, magnetic, and electronic properties of small Fe clusters. It is shown that, while the lowest-energy isomers of Fe3 and Fe4 obtained in the framework of density functional theory within the generalized gradient approximation (GGA) are characterized by Jahn-Teller-like distortions away from the most regular shapes (which is in agreement with other works), these distortions are reduced when electron correlation effects are considered explicitly as within the GGA+U approach. At the same time, the magnetic moments of the clusters are enhanced with respect to the pure GGA case, resulting in maximal moments (in the sense of Hund’s rules) of 4 μB per atom for the ground state structures of Fe3 and Fe4, and a total moment of 18 μB for Fe5. This already happens for moderate values of the Coulomb repulsion parameter U̴ 2.0 eV and is explained by changes in the electronic structures of the clusters.

STRUCTURE AND MAGNETIC PROPERTIES OF Co12X(X = Ni, Ag, Pt, Au) CLUSTERS

2007 ◽  
Vol 21 (30) ◽  
pp. 5091-5098 ◽  
Author(s):  
Q. L. LU ◽  
J. C. JIANG ◽  
J. G. WAN ◽  
G. H. WANG
Keyword(s):  
Density Functional ◽  
Magnetic Moments ◽  
Stable Configuration ◽  
Many Body ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Au Clusters ◽  
The Density Functional Theory ◽  
Ground State Structures ◽  
Body Potential

The ground state structures of Co 12 X ( X = Ni , Ag , Pt , Au ) clusters are obtained by a genetic algorithm with a Gupta-like many-body potential, and further optimized using the density functional theory with generalized gradient approximation. The structures of Co 12 X have a slightly distorted icosahedral pattern. The X atom is on the surface for the most stable configuration. Their total magnetic moments are 0μ B , 3μ B , 21μ B , and 22μ B , respectively. The reasons for the reduction of magnetism of Co 12 X are discussed in detail.

STRUCTURE STABILITY AND ELECTRONIC PROPERTIES OF CumConCO (m+n=2–7) CLUSTERS

2016 ◽  
Vol 24 (04) ◽  
pp. 1750049 ◽  
Author(s):  
JUN ZHU ◽  
XIU-RONG ZHANG ◽  
PEI-YING HUO ◽  
ZHI-CHENG YU
Keyword(s):  
Electronic Properties ◽  
Ground State ◽  
Density Functional ◽  
Adsorption Process ◽  
Magnetic Moments ◽  
Structure Stability ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Adsorption Energies ◽  
Ground State Structures

The structure stability and electronic properties of CumConCO ([Formula: see text]–7) clusters have been systematically investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). The results indicate that the ground state structures of CumConCO clusters obtained by adsorbing CO molecules on the top sites of stable CumConclusters with C atoms and CO molecules have been activated during adsorption process. Cu2CO, CuCoCO, Cu3CoCO, Co4CO, Cu4CoCO and Cu3Co3CO clusters are stronger than other ground state clusters in thermodynamic stability. Cu2CO, Cu4CO and Cu6CO clusters show stronger chemical stability; Co2CO, Co4CO, Cu5CoCO, Cu3Co3CO, Cu2Co5CO and Co7CO clusters show better propensity to adsorb CO for these clusters have larger adsorption energies; Electronic states of Cu2Co3CO, CuCo4CO, Co5CO, Cu4Co3CO, Cu3Co4CO, CuCo6CO and Co7CO clusters are mainly influenced by those of 3d orbitals in Co and Cu atoms, the contribution to total magnetic moments of these clusters comes mainly from Co atoms and these clusters have high magnetism.

IRON IMPURITY IN ZIRCON BY DFT COMPUTATIONS

2013 ◽  
Vol 27 (20) ◽  
pp. 1350145 ◽  
Author(s):  
ARVIDS STASHANS ◽  
KRUPSKAYA RIVERA
Keyword(s):  
Density Functional ◽  
Coulomb Repulsion ◽  
Local Magnetic Moment ◽  
Generalized Gradient ◽  
Functional Formalism ◽  
Strong Electron ◽  
Functional Theory ◽  
Defective Region ◽  
Electron Correlation Effects ◽  
Work First

A single Fe impurity impact on the properties of ZrSiO 4 low pressure phase (zircon) has been addressed in the present work. First-principles density functional theory and generalized gradient approximation have been exploited throughout the study. Strong electron correlation effects not included in the density-functional formalism are treated by a Hubbard-type on-site Coulomb repulsion approach. Our results provide evidence over occurrence of a local magnetic moment in the material. Reduction in the band-gap width, changes in chemical bonding and microstructure of the defective region have been discussed as well.

scholarly journals Impact of Nano-Scale Distribution of Atoms on Electronic and Magnetic Properties of Phases in Fe-Al Nanocomposites: An Ab Initio Study

Nanomaterials ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 1059 ◽  
Author(s):  
Ivana Miháliková ◽  
Martin Friák ◽  
Yvonna Jirásková ◽  
David Holec ◽  
Nikola Koutná ◽  
...  
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Nearest Neighbor ◽  
Magnetic Moments ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Α Phase ◽  
Ordered Intermetallic ◽  
Random Structures ◽  
The Impact

Quantum-mechanical calculations are applied to examine magnetic and electronic properties of phases appearing in binary Fe-Al-based nanocomposites. The calculations are carried out using the Vienna Ab-initio Simulation Package which implements density functional theory and generalized gradient approximation. The focus is on a disordered solid solution with 18.75 at. % Al in body-centered-cubic ferromagnetic iron, so-called α -phase, and an ordered intermetallic compound Fe 3 Al with the D0 3 structure. In order to reveal the impact of the actual atomic distribution in the disordered Fe-Al α -phase three different special quasi-random structures with or without the 1st and/or 2nd nearest-neighbor Al-Al pairs are used. According to our calculations, energy decreases when eliminating the 1st and 2nd nearest neighbor Al-Al pairs. On the other hand, the local magnetic moments of the Fe atoms decrease with Al concentration in the 1st coordination sphere and increase if the concentration of Al atoms increases in the 2nd one. Furthermore, when simulating Fe-Al/Fe 3 Al nanocomposites (superlattices), changes of local magnetic moments of the Fe atoms up to 0.5 μ B are predicted. These changes very sensitively depend on both the distribution of atoms and the crystallographic orientation of the interfaces.

scholarly journals Many-Body Effects in FeN4 Center Embedded in Graphene

2020 ◽  
Vol 10 (7) ◽  
pp. 2542 ◽  
Author(s):  
Andrew Allerdt ◽  
Hasnain Hafiz ◽  
Bernardo Barbiellini ◽  
Arun Bansil ◽  
Adrian E. Feiguin
Keyword(s):  
Transition Metal Complexes ◽  
First Principles ◽  
Density Functional ◽  
Coulomb Repulsion ◽  
Density Matrix Renormalization Group ◽  
Orbital Interaction ◽  
Many Body ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Density Matrix Renormalization

We introduce a computational approach to study porphyrin-like transition metal complexes, bridging density functional theory and exact many-body techniques, such as the density matrix renormalization group (DMRG). We first derive a multi-orbital Anderson impurity Hamiltonian starting from first principles considerations that qualitatively reproduce generalized gradient approximation (GGA)+U results when ignoring inter-orbital Coulomb repulsion U ′ and Hund exchange J. An exact canonical transformation is used to reduce the dimensionality of the problem and make it amenable to DMRG calculations, including all many-body terms (both intra- and inter-orbital), which are treated in a numerically exact way. We apply this technique to FeN 4 centers in graphene and show that the inclusion of these terms has dramatic effects: as the iron orbitals become single occupied due to the Coulomb repulsion, the inter-orbital interaction further reduces the occupation, yielding a non-monotonic behavior of the magnetic moment as a function of the interactions, with maximum polarization only in a small window at intermediate values of the parameters. Furthermore, U ′ changes the relative position of the peaks in the density of states, particularly on the iron d z 2 orbital, which is expected to affect the binding of ligands greatly.

POSSIBLE Si-BASED HALF-METALLIC MATERIALS: MnSi46 CLATHRATES

2012 ◽  
Vol 26 (18) ◽  
pp. 1250114
Author(s):  
ZHI-WEI ZHAO ◽  
JING WANG ◽  
HUI-YAN ZHAO ◽  
YING LIU
Keyword(s):  
Density Functional ◽  
Magnetic Moments ◽  
Density Functional Theory Calculations ◽  
Metallic Materials ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Half Metallic ◽  
Silicon Clathrates ◽  
Ni Dopant ◽  
Center Site

The structural and magnetic properties of M Si 46 (M = Mn , Fe , Co and Ni ) clathrates have been studied using density functional theory calculations within the generalized gradient approximation. When the structures involve a dopant at the center of a Si 20 or Si 24 cage, the results show that the neighboring atoms around the dopant are drawn in toward the center. Some of the silicon clathrates with a Mn or Co dopant at the center site of a Si 20 cage, or a Mn , Fe or Ni dopant at the center site of a Si 24 cage are found to be half-metallic materials with large magnetic moments, and others with a Fe or Ni dopant at the center site of a Si 20 cage or a Co dopant at the center site of a Si 24 cage display semi-metallic characters. In particular, MnSi 46 with a half-metallic gap of 0.70 eV and a magnetic moment of 5.00 μ B shows promise for applications in the field of spintronics.

MAGNETIC MAP OF MnNi ALLOYED MONOLAYER ON Cu(001) SUBSTRATE: AB-INITIO CALCULATIONS

2010 ◽  
Vol 09 (06) ◽  
pp. 619-622
Author(s):  
BOTHINA A. HAMAD
Keyword(s):  
Density Functional ◽  
Theoretical Study ◽  
Magnetic Moments ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Generalized Gradient Approximation ◽  
Exchange Correlation Potential ◽  
The Density Functional Theory ◽  
Correlation Potential

In this work, a theoretical study of the structural, electronic and magnetic properties are presented for Mn 0.5 Ni 0.5 alloyed overlayer adsorbed on Cu (001) surface. The calculations were performed using the density functional theory (DFT) and the exchange-correlation potential was treated by the generalized gradient approximation (GGA). The system was fully relaxed except for the central layer, which yields to outward relaxations and inward Mn and Ni surface atoms, respectively in the ferromagnetic and antiferromagnetic configurations. The in-plane ferromagnetic configuration was found to be more stable than the antiferromagnetic one by 25 meV/atom. The local magnetic moments of Mn atoms were found to be about 4 μ B , whereas those of the Ni atoms where found to be 0.46 μ B .

Structures and stabilities of (OsnN)0,±(n = 7 − 11) clusters

2015 ◽  
Vol 29 (23) ◽  
pp. 1550163
Author(s):  
W. L. Guo ◽  
L. L. Zhang ◽  
M. Luo ◽  
X. R. Zhang
Keyword(s):  
Density Functional Theory ◽  
Ionization Potential ◽  
Electron Affinity ◽  
Ground State ◽  
Density Functional ◽  
Magic Number ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Generalized Gradient Approximation ◽  
Ground State Structures

Structures and stabilities of [Formula: see text] clusters have been systematically studied via using density functional theory (DFT) with generalized gradient approximation (GGA). The calculations show that the stable configurations of [Formula: see text] are such structures with one N atom bonded to the external of the basic constructions consisting of Os atoms. Meanwhile, [Formula: see text] clusters [Formula: see text] represent “magic number” effect, and 8 is the magic number. Additionally, the ground-state structures of [Formula: see text] clusters have the best stability, while that of [Formula: see text] cluster possesses the worst stability. The result of the study on the ionization potential (IP) and the electron affinity (EA) shows that there are not topological differences among the configurations of [Formula: see text][Formula: see text] clusters.

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