Pseudopotential calculations of relaxation and formation energy of a vacancy in aluminum

The density functional pseudopotential simulation was carried out to study dissociation of the H2O molecule on the TiO2 anatase surface (pure and W doped). Formation and desorption of the OH groups were studied, and it was shown that the adding of tungsten into titanium dioxide leads to reduction of the desorption energy of OH groups from 6.06 eV to 4.74 eV. Creation of the hydrogen peroxide H2O2 molecules was also investigated. Substitution of Ti with W on the TiO2 anatase surface decreases the formation energy of hydrogen peroxide molecules and moves it up to the range of visible sun light. Decrease of the formation energy of free OH groups and H2O2 molecules, which are fissile oxidizers, increases their quantity in water and promotes increase in effectiveness of organic pollutants decomposition.

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Ab initio band theory approach to electron energy loss near edge structures

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100104595 ◽

1988 ◽

Vol 46 ◽

pp. 506-507

Author(s):

Xudong Weng ◽

O.F. Sankey ◽

Peter Rez

Keyword(s):

Ab Initio ◽

Local Density ◽

Interpolation Method ◽

Atomic Orbital ◽

Plane Waves ◽

Large Set ◽

Theory Approach ◽

Band Theory ◽

Atomic Orbitals ◽

Pseudopotential Calculations

Single electron band structure techniques have been applied successfully to the interpretation of the near edge structures of metals and other materials. Among various band theories, the linear combination of atomic orbital (LCAO) method is especially simple and interpretable. The commonly used empirical LCAO method is mainly an interpolation method, where the energies and wave functions of atomic orbitals are adjusted in order to fit experimental or more accurately determined electron states. To achieve better accuracy, the size of calculation has to be expanded, for example, to include excited states and more-distant-neighboring atoms. This tends to sacrifice the simplicity and interpretability of the method.In this paper. we adopt an ab initio scheme which incorporates the conceptual advantage of the LCAO method with the accuracy of ab initio pseudopotential calculations. The so called pscudo-atomic-orbitals (PAO's), computed from a free atom within the local-density approximation and the pseudopotential approximation, are used as the basis of expansion, replacing the usually very large set of plane waves in the conventional pseudopotential method. These PAO's however, do not consist of a rigorously complete set of orthonormal states.

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Tuning the optoelectronic properties of hematite with rhodium doping for photoelectrochemical water splitting using density functional theory approach

Scientific Reports ◽

10.1038/s41598-020-78824-y ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Abdur Rauf ◽

Muhammad Adil ◽

Shabeer Ahmad Mian ◽

Gul Rahman ◽

Ejaz Ahmed ◽

...

Keyword(s):

Density Functional Theory ◽

Optical Properties ◽

Optical Absorption ◽

Water Splitting ◽

Density Functional ◽

Formation Energy ◽

Visible Region ◽

Photoelectrochemical Water Splitting ◽

Theory Approach ◽

Functional Theory

AbstractHematite (Fe2O3) is one of the best candidates for photoelectrochemical water splitting due to its abundance and suitable bandgap. However, its efficiency is mostly impeded due to the intrinsically low conductivity and poor light absorption. In this study, we targeted this intrinsic behavior to investigate the thermodynamic stability, photoconductivity and optical properties of rhodium doped hematite using density functional theory. The calculated formation energy of pristine and rhodium doped hematite was − 4.47 eV and − 5.34 eV respectively, suggesting that the doped material is thermodynamically more stable. The DFT results established that the bandgap of doped hematite narrowed down to the lower edge (1.61 eV) in the visible region which enhanced the optical absorption and photoconductivity of the material. Moreover, doped hematite has the ability to absorb a broad spectrum (250–800) nm. The enhanced optical absorption boosted the photocurrent and incident photon to current efficiency. The calculated results also showed that the incorporation of rhodium in hematite induced a redshift in optical properties.

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Role of Oxygen Vacancy Formation Energy and Insulating Behavior in Darkening of White Amorphous TiO2

The Journal of Physical Chemistry C ◽

10.1021/acs.jpcc.1c02599 ◽

2021 ◽

Author(s):

D. Nanda Gopala Krishna ◽

R.P. George ◽

John Philip

Keyword(s):

Oxygen Vacancy ◽

Formation Energy ◽

Vacancy Formation Energy ◽

Vacancy Formation ◽

Oxygen Vacancy Formation ◽

Amorphous Tio2

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On the Effects of Doping on the Catalytic Performance of (La,Sr)CoO3. A DFT Study of CO Oxidation

Catalysts ◽

10.3390/catal9040312 ◽

2019 ◽

Vol 9 (4) ◽

pp. 312 ◽

Cited By ~ 2

Author(s):

Antonella Glisenti ◽

Andrea Vittadini

Keyword(s):

Catalytic Activity ◽

Co Oxidation ◽

Density Functional Calculations ◽

Density Functional ◽

Formation Energy ◽

Oxygen Vacancies ◽

Catalytic Performance ◽

Energy Profiles ◽

High Concentrations ◽

3D Impurities

The effects of modifying the composition of LaCoO3 on the catalytic activity are predicted by density functional calculations. Partially replacing La by Sr ions has benefical effects, causing a lowering of the formation energy of O vacancies. In contrast to that, doping at the Co site is less effective, as only 3d impurities heavier than Co are able to stabilize vacancies at high concentrations. The comparison of the energy profiles for CO oxidation of undoped and of Ni-, Cu-m and Zn-doped (La,Sr)CoO3(100) surface shows that Cu is most effective. However, the effects are less spectacular than in the SrTiO3 case, due to the different energetics for the formation of oxygen vacancies in the two hosts.

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Research on Molecular Structure and Electronic Properties of Ln3+ (Ce3+, Tb3+, Pr3+)/Li+ and Eu2+ Co-Doped Sr2Si5N8 via DFT Calculation

Molecules ◽

10.3390/molecules26071849 ◽

2021 ◽

Vol 26 (7) ◽

pp. 1849

Author(s):

Ziqian Yin ◽

Meijuan Li ◽

Jianwen Zhang ◽

Qiang Shen

Keyword(s):

Molecular Structure ◽

Energy Level ◽

Density Functional ◽

Formation Energy ◽

Electronic Band Structure ◽

Blue Shift ◽

Lanthanide Ions ◽

Partial Replacement ◽

Electronic Band ◽

Charge Imbalance

We use density functional theory (DFT) to study the molecular structure and electronic band structure of Sr2Si5N8:Eu2+ doped with trivalent lanthanides (Ln3+ = Ce3+, Tb3+, Pr3+). Li+ was used as a charge compensator for the charge imbalance caused by the partial replacement of Sr2+ by Ln3+. The doping of Ln lanthanide atom causes the structure of Sr2Si5N8 lattice to shrink due to the smaller atomic radius of Ln3+ and Li+ compared to Sr2+. The doped structure’s formation energy indicates that the formation energy of Li+, which is used to compensate for the charge imbalance, is the lowest when the Sr2 site is doped. Thus, a suitable Li+ doping site for double-doped lanthanide ions can be provided. In Sr2Si5N8:Eu2+, the doped Ce3+ can occupy partly the site of Sr12+ ([SrN8]), while Eu2+ accounts for Sr12+ and Sr22+ ([SrN10]). When the Pr3+ ion is selected as the dopant in Sr2Si5N8:Eu2+, Pr3+ and Eu2+ would replace Sr22+ simultaneously. In this theoretical model, the replacement of Sr2+ by Tb3+ cannot exist reasonably. For the electronic structure, the energy level of Sr2Si5N8:Eu2+/Li+ doped with Ce3+ and Pr3+ appears at the bottom of the conduction band or in the forbidden band, which reduces the energy bandgap of Sr2Si5N8. We use DFT+U to adjust the lanthanide ion 4f energy level. The adjusted 4f-CBM of CeSr1LiSr1-Sr2Si5N8 is from 2.42 to 2.85 eV. The energy range of 4f-CBM in PrSr1LiSr1-Sr2Si5N8 is 2.75–2.99 eV and its peak is 2.90 eV; the addition of Ce3+ in EuSr1CeSr1LiSr1 made the 4f energy level of Eu2+ blue shift. The addition of Pr3+ in EuSr2PrSr2LiSr1 makes part of the Eu2+ 4f energy level blue shift. Eu2+ 4f energy level in EuSr2CeSr1LiSr1 is not in the forbidden band, so Eu2+ is not used as the emission center.

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

MRS Proceedings ◽

10.1557/proc-0902-t10-46 ◽

2005 ◽

Vol 902 ◽

Cited By ~ 2

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.

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