Iron in Hydroxyapatite: Interstitial or Substitution Sites?

Iron-doped hydroxyapatite (Fe-HAp) is regarded as a promising magnetic material with innate biocompatibility. Despite the many studies reported in the literature, a detailed theoretical description of Fe inclusions is still missing. There is even no consensual view on what kind of Fe defects take place in Fe-HAp—iron interstitial or calcium substitutions? In order to address these questions, we employ modern first-principles methodologies, including hybrid density functional theory, to find the geometry, electronic, magnetic and thermodynamic properties of iron impurities in Fe-HAp. We consider a total of 26 defect configurations, including substitutional (phosphorus and calcium sites) and interstitial defects. Formation energies are estimated considering the boundaries of chemical potentials in stable hydroxyapatite. We show that the most probable defect configurations are: Fe3+ and Fe2+ substitutions of Ca(I) and Ca(II) sites under Ca-poor conditions. Conversely, Fe interstitials near the edge of the hydroxyl channel are favored in Ca-rich material. Substitutional Fe on the P site is also a probable defect, and unlike the other forms of Fe, it adopts a low-spin state. The analysis of Fe K-XANES spectra available in the literature shows that Fe-HAp usually contains iron in different configurations.

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Ab Initio Study of MgSe Self-Interstitial (Mgi and Sei)

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.242.440 ◽

2015 ◽

Vol 242 ◽

pp. 440-446 ◽

Cited By ~ 6

Author(s):

Emmanuel Igumbor ◽

Kingsley Obodo ◽

Water E. Meyer

Keyword(s):

Transition State ◽

Density Functional ◽

Local Density ◽

Shallow Donor ◽

Generalized Gradient ◽

Functional Theory ◽

Interstitial Defects ◽

Frame Work ◽

Formation Energies

We present detailed calculations of formation and thermodynamics transition state energies of Mgiand Seiinterstitial defects in MgSe using generalized gradient approximation (GGA) and local density approximation (LDA) functional in the frame work of density functional theory (DFT). For both LDA and GGA the formation energies of Mgiand Seiare relatively low in all the configurations. The most stable Se interstitial was the tetrahedral (T) configuration having lower formation energy than the decagonal (D) configuration. TheMgiand Seidefect introduced transition state levels that had either donor or acceptor levels within the band gap. Seiacts as a donor or an acceptor and creates levels that were either deep or shallow depending on the configuration. Seiexhibit negative-U properties and show charge states metastability in the D configuration. Mgiacts as only shallow donor (+2/ + 1) in both T and D configurations, in addition we pointed out the role of Mgias electrically activating donor.

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First-Principles Study of N Impurities in SiC Polytypes

MRS Proceedings ◽

10.1557/proc-510-181 ◽

1998 ◽

Vol 510 ◽

Cited By ~ 2

Author(s):

W. Windl ◽

A. A. Demkov

Keyword(s):

Density Functional Theory ◽

Electronic Properties ◽

First Principles ◽

Density Functional ◽

Binding Energies ◽

Functional Theory ◽

Native Defects ◽

High Binding ◽

Interstitial Defects ◽

Formation Energies

AbstractWe investigate theoretically the energetics of nitrogen impurities in β-SiC, their geometrical relaxation, and electronic properties. We find that density-functional theory is able to calculate donor-ionization energies accurately once large enough simulation cells are used. For neutral interstitial defects, we find that configurations where N is three-fold coordinated have very low formation energies and high binding energies with the involved native defects. At the same time, such configurations introduce deep levels into the gap which may result in a non-activation of the donor

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Two-dimensional g-C3N4/Ti2CO2 heterostructure as a direct Z-scheme photocatalyst for water splitting: A hybrid density functional theory investigation

Physica E Low-dimensional Systems and Nanostructures ◽

10.1016/j.physe.2021.114872 ◽

2021 ◽

pp. 114872

Author(s):

X. Liu ◽

W. Kang ◽

L. Qi ◽

J. Zhao ◽

Y. Wang ◽

...

Keyword(s):

Density Functional Theory ◽

Water Splitting ◽

Density Functional ◽

Hybrid Density Functional Theory ◽

Two Dimensional ◽

Functional Theory ◽

Hybrid Density Functional

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Hybrid Density Functional Theory Study on Structural and Optoelectronic Properties of ZnSe1–xTex for the Photocatalytic Applications

The Journal of Physical Chemistry C ◽

10.1021/acs.jpcc.1c03670 ◽

2021 ◽

Author(s):

Sajjad Hussain ◽

Lingju Guo ◽

Tao He

Keyword(s):

Density Functional Theory ◽

Density Functional ◽

Optoelectronic Properties ◽

Hybrid Density Functional Theory ◽

Density Functional Theory Study ◽

Functional Theory ◽

Structural And Optoelectronic Properties ◽

Hybrid Density Functional ◽

Photocatalytic Applications

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On the Many-Body Expansion of an Interaction Energy of Some Supramolecular Halogen-Containing Capsules

Molecules ◽

10.3390/molecules26154431 ◽

2021 ◽

Vol 26 (15) ◽

pp. 4431

Author(s):

Jiří Czernek ◽

Jiří Brus

Keyword(s):

Density Functional ◽

Condensed Phases ◽

Multicomponent Mixtures ◽

Many Body ◽

Symmetric Form ◽

Functional Theory ◽

Emergent Features ◽

The Many ◽

Surprising Fact ◽

Dimethyl Benzene

A tetramer model was investigated of a remarkably stable iodine-containing supramolecular capsule that was most recently characterized by other authors, who described emergent features of the capsule’s formation. In an attempt to address the surprising fact that no strong pair-wise interactions between any of the respective components were experimentally detected in condensed phases, the DFT (density-functional theory) computational model was used to decompose the total stabilization energy as a sum of two-, three- and four-body contributions. This model considers complexes formed between either iodine or bromine and the crucial D4h-symmetric form of octaaryl macrocyclic compound cyclo[8](1,3-(4,6-dimethyl)benzene that is surrounded by arenes of a suitable size, namely, either corannulene or coronene. A significant enthalpic gain associated with the formation of investigated tetramers was revealed. Furthermore, it is shown that the total stabilization of these complexes is dominated by binary interactions. Based on these findings, comments are made regarding the experimentally observed behavior of related multicomponent mixtures.

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Efficient charge separation and visible-light response in bilayer HfS2-based van der Waals heterostructures

RSC Advances ◽

10.1039/c8ra03047b ◽

2018 ◽

Vol 8 (34) ◽

pp. 18889-18895 ◽

Cited By ~ 10

Author(s):

Biao Wang ◽

Xukai Luo ◽

Junli Chang ◽

Xiaorui Chen ◽

Hongkuan Yuan ◽

...

Keyword(s):

Charge Separation ◽

Density Functional ◽

Van Der Waals ◽

Light Response ◽

Hybrid Density Functional Theory ◽

Functional Theory ◽

Visible Light Response ◽

Efficient Charge ◽

Hybrid Density Functional ◽

Photocatalytic Applications

In this work, we employ hybrid density functional theory to investigate HfS2-based van der Waals (vdW) heterojunctions for highly efficient photovoltaic and photocatalytic applications.

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Activity of faujasite supported gold monomer towards water gas shift reaction: hybrid density functional theory/molecular mechanics approach

RSC Advances ◽

10.1039/c5ra13962g ◽

2015 ◽

Vol 5 (96) ◽

pp. 78864-78873 ◽

Cited By ~ 1

Author(s):

Subhi Baishya ◽

Ramesh Ch. Deka

Keyword(s):

Density Functional ◽

Water Gas Shift ◽

Hybrid Density Functional Theory ◽

Water Gas Shift Reaction ◽

Functional Theory ◽

Cationic Monomer ◽

Shift Reaction ◽

Supported Gold ◽

Water Gas ◽

Hybrid Density Functional

Neutral gold monomer supported on faujasite (Au0/FAU) exhibits superior catalytic activity towards water gas shift reaction compared to cationic monomer.

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Hybrid Density Functional Theory Studies on the Magnetic Interactions and the Weak Covalent Bonding for the Phenalenyl Radical Dimeric Pair

Journal of the American Chemical Society ◽

10.1021/ja0177197 ◽

2002 ◽

Vol 124 (37) ◽

pp. 11122-11130 ◽

Cited By ~ 76

Author(s):

Yu Takano ◽

Takeshi Taniguchi ◽

Hiroshi Isobe ◽

Takashi Kubo ◽

Yasushi Morita ◽

...

Keyword(s):

Density Functional Theory ◽

Density Functional ◽

Covalent Bonding ◽

Magnetic Interactions ◽

Hybrid Density Functional Theory ◽

Functional Theory ◽

Hybrid Density Functional

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DFT study on thermo-elastic properties of Ru2FeZ (Z = Si, Ge, Sn) Heusler alloys

International Journal of Modern Physics B ◽

10.1142/s0217979218500455 ◽

2018 ◽

Vol 32 (05) ◽

pp. 1850045 ◽

Cited By ~ 7

Author(s):

Aneeza Iftikhar ◽

Afaq Ahmad ◽

Iftikhar Ahmad ◽

Muhammad Rizwan

Keyword(s):

Thermal Stability ◽

Elastic Properties ◽

Density Functional ◽

Heusler Alloys ◽

Longitudinal Mode ◽

Transverse Mode ◽

Functional Theory ◽

Formation Energies ◽

Thermal Stability Of ◽

Temperature Melting

We studied the thermo-elastic properties of Ru2FeZ (Z[Formula: see text]=[Formula: see text]Si, Ge, Sn) Heusler alloys within the framework of density functional theory. Thermo-elastic properties corresponding to elastic modulus, anisotropy, phase stability, elastic wave velocities, thermal stability, Debye temperature, melting temperature, thermal conductivity and formation energy are calculated. The elastic constants C[Formula: see text] predict the structural and dynamical stabilities while the formation energies show thermal stability of the alloys at 0 K. Pugh’s and Poisson’s ratios display the ductile nature of alloys. All alloys are anisotropic and we also observed that Ru2FeSn is the hardest material than Ru2FeSi and Ru2FeGe. Moreover, longitudinal mode of vibrations are also observed and are maximum along [100], [110] and [111] directions than the transverse mode of vibrations.

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