Theoretical Studies of GaAs on Si

1989 ◽  
Vol 159 ◽  
Author(s):  
John E. Northrup
Keyword(s):  
Density Functional ◽  
Exchange Reactions ◽  
Functional Formalism ◽  
Bulk Gaas ◽  
Interface Dipole ◽  
Gaas On Si ◽  
Chemical Potentials ◽  
Metastable Structure ◽  
Si Films ◽  
Formation Energies

ABSTRACTThe energies of various two-dimensional GaAs on Si films have been calculated using the first principles pseudopotential method and density functional formalism. For GaAs on Si(111), the structures formed by adding a bilayer of GaAs to Si(111)1×1:As are shown to have positive formation energies, even after exchange reactions which eliminate the interface dipole are allowed. For GaAs on Si(100), the dependence of the formation energy of the films on the chemical potentials of the atomic constituents has been calculated. In the limit where μAs=μAs(bulk), and assuming the films have equilibrated with a bulk GaAs reservoir (μGa + μAs = μGaAs (bulk)), the lowest energy film is found to be the Si(100)2×1:As surface. In the opposite limit, μGa=μGa(bulk), the lowest energy film is the Si(100)2×1:(GaAs) surface. A new metastable structure obtained by adding 1/2 monolayer of Ga to Si(100)2×l:As has been studied.

First-principles Studies of Phase Stability and the Neutral Atomic Vacancies in LiNbO3, NaNbO3 and KNbO3

2005 ◽  
Vol 902 ◽  
Author(s):  
Akio Shigemi ◽  
Takahiro Wada
Keyword(s):  
Enthalpy Of Formation ◽  
Density Functional ◽  
Formation Energy ◽  
Type Structure ◽  
Enthalpies Of Formation ◽  
Functional Formalism ◽  
Reducing Atmosphere ◽  
Perovskite Type Oxide ◽  
Formation Energies ◽  
Perovskite Type

AbstractWe overall evaluated the enthalpies of formation and the formation energies of neutral vacancies in ANbO3 (A = Li, Na, K) using a plane-wave pseudopotential method within a density functional formalism. The LiNbO3 phase with the LiNbO3-type structure was confirmed to have lower enthalpy of formation than that with perovskite- or ilmenite-type structure. The NaNbO3 (R3c) and KNbO3 (Bmm2 and R3m) phases with the lowest symmetry were found to have the lowest enthalpy of formation. The formation energy of a A vacancy was found to be the lowest under an oxidizing atmosphere and that of an O vacancy was found to be the lowest under a reducing atmosphere. The formation energy of a Nb vacancy was the highest under both oxygen-rich and -poor conditions. These results are in agreement with the empirical rule that B site defects in perovskite-type oxide do not exist.

scholarly journals Iron in Hydroxyapatite: Interstitial or Substitution Sites?

Nanomaterials ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2978
Author(s):  
Leon Avakyan ◽  
Ekaterina Paramonova ◽  
Vladimir Bystrov ◽  
José Coutinho ◽  
Sandrine Gomes ◽  
...  
Keyword(s):  
Density Functional ◽  
Theoretical Description ◽  
Functional Theory ◽  
Chemical Potentials ◽  
Interstitial Defects ◽  
Rich Material ◽  
The Many ◽  
Hybrid Density Functional ◽  
Formation Energies ◽  
Substitutional Fe

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.

Some Approximate Atomic and Molecular Energy Formulas

2003 ◽  
Vol 68 (1) ◽  
pp. 61-74 ◽  
Author(s):  
Peter Politzer ◽  
Abraham F. Jalbout ◽  
Ping Jin
Keyword(s):  
Density Functional ◽  
Electrostatic Potentials ◽  
Hartree Fock ◽  
Chemical Potentials ◽  
Approximate Formulas

We have tested several approximate formulas that relate atomic and molecular energies to the electrostatic potentials at the nuclei, V0 and V0,A, respectively. They are based upon the assumption that the chemical potentials can be neglected relative to V0 and V0,A. Exact, Hartree-Fock and density-functional values were used for the latter. The results are overall encouraging; the errors in the energies generally decrease markedly as the nuclear charges Z increase and the assumptions become more valid. Improvement is needed, however, in fitting the V0 and V0,A to Z.

scholarly journals Effect of vacancy defects on the electronic transport properties of an Ag–ZnO–Pt sandwich structure

2021 ◽  
Vol 20 (2) ◽  
pp. 798-804
Author(s):  
G. R. Berdiyorov ◽  
F. Boltayev ◽  
G. Eshonqulov ◽  
H. Hamoudi
Keyword(s):  
Transport Properties ◽  
Electronic Transport ◽  
Density Functional ◽  
Practical Importance ◽  
Functional Formalism ◽  
Vacancy Defects ◽  
Electronic Transport Properties ◽  
Charge Localization ◽  
Metal Insulator Metal ◽  
Current Rectification

AbstractThe effect of zinc and oxygen vacancy defects on the electronic transport properties of Ag(100)–ZnO(100)–Pt(100) sandwich structures is studied using density functional theory in combination with the nonequilibrium Green’s functional formalism. Defect-free systems show clear current rectification due to voltage dependent charge localization in the system as revealed in our transmission eigenstates analysis. Regardless of the location, oxygen vacancies result in enhanced current in the system, whereas Zn vacancy defects reduce the charge transport across the junction. The current rectification becomes less pronounced in the presence of both types of vacancy defects. Our findings can be of practical importance for developing metal-insulator-metal diodes.

scholarly journals Effect of chemical modification on electronic transport properties of carbyne

2021 ◽  
Author(s):  
G. R. Berdiyorov ◽  
U. Khalilov ◽  
H. Hamoudi ◽  
Erik C. Neyts
Keyword(s):  
Transport Properties ◽  
Electronic Transport ◽  
Density Functional ◽  
Structural Changes ◽  
Carbon Chain ◽  
Functional Formalism ◽  
Functional Theory ◽  
Carbon Allotrope ◽  
Electronic Transport Properties ◽  
Interface Structures

AbstractUsing density functional theory in combination with the Green’s functional formalism, we study the effect of surface functionalization on the electronic transport properties of 1D carbon allotrope—carbyne. We found that both hydrogenation and fluorination result in structural changes and semiconducting to metallic transition. Consequently, the current in the functionalization systems increases significantly due to strong delocalization of electronic states along the carbon chain. We also study the electronic transport in partially hydrogenated carbyne and interface structures consisting of pristine and functionalized carbyne. In the latter case, current rectification is obtained in the system with rectification ratio up to 50%. These findings can be useful for developing carbyne-based structures with tunable electronic transport properties.

Magnetic Properties of Embedded Rh Clusters in Ni Matrix

1995 ◽  
Vol 384 ◽  
Author(s):  
Zhi-Qiang Li ◽  
Yuichi Hashi ◽  
Jing-Zhi Yu ◽  
Kaoru Ohno ◽  
Yoshiyuki Kawazoe
Keyword(s):  
Magnetic Properties ◽  
Electronic Structure ◽  
First Principles ◽  
Density Functional ◽  
Local Density ◽  
Magnetic Moments ◽  
Functional Formalism ◽  
Rhodium Clusters ◽  
Spin Polarized ◽  
Local Density Functional

ABSTRACTThe electronic structure and magnetic properties of rhodium clusters with sizes of 1 - 43 atoms embedded in the nickel host are studied by the first-principles spin-polarized calculations within the local density functional formalism. Single Rh atom in Ni matrix is found to have magnetic moment of 0.45μB. Rh13 and Rhl 9 clusters in Ni matrix have lower magnetic moments compared with the free ones. The most interesting finding is tha.t Rh43 cluster, which is bulk-like nonmagnetic in vacuum, becomes ferromagnetic when embedded in the nickel host.

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

2018 ◽  
Vol 32 (05) ◽  
pp. 1850045 ◽  
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.

scholarly journals Dumbbell configuration of silicon adatom defects on silicene nanoribbons

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Huynh Anh Huy ◽  
Quoc Duy Ho ◽  
Truong Quoc Tuan ◽  
Ong Kim Le ◽  
Nguyen Le Hoai Phuong
Keyword(s):  
Magnetic Properties ◽  
Band Gap ◽  
Density Functional ◽  
Spin Moment ◽  
Hydrogen Atoms ◽  
Functional Theory ◽  
Electronic And Magnetic Properties ◽  
Spin Degeneracy ◽  
Silicene Nanoribbons ◽  
Formation Energies

AbstractUsing density functional theory (DFT), we performed theoretical investigation on structural, energetic, electronic, and magnetic properties of pure armchair silicene nanoribbons with edges terminated with hydrogen atoms (ASiNRs:H), and the absorptions of silicon (Si) atom(s) on the top of ASiNRs:H. The calculated results show that Si atoms prefer to adsorb on the top site of ASiNRs:H and form the single- and/or di-adatom defects depending on the numbers. Si absorption defect(s) change electronic and magnetic properties of ASiNRs:H. Depending on the adsorption site the band gap of ASiNRs:H can be larger or smaller. The largest band gap of 1 Si atom adsorption is 0.64 eV at site 3, the adsorption of 2 Si atoms has the largest band gap of 0.44 eV at site 1-D, while the adsorption at sites5 and 1-E turn into metallic. The formation energies of Si adsorption show that adatom defects in ASiNRs:H are more preferable than pure ASiNRs:H with silicon atom(s). 1 Si adsorption prefers to be added on the top site of a Si atom and form a single-adatom defect, while Si di-adatom defect has lower formation energy than the single-adatom and the most energetically favorable adsorption is at site 1-F. Si adsorption atoms break spin-degeneracy of ASiNRs:H lead to di-adatom defect at site 1-G has the highest spin moment. Our results suggest new ways to engineer the band gap and magnetic properties silicene materials.

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