The electronic structure of alkali doped alkaline earth metal oxides: Li doping of MgO studied with DFT-GGA and GGA+U

Nolan, Michael; Watson, Graeme W.

doi:10.1016/j.susc.2005.04.046

Cited by 69 publications

(78 citation statements)

References 31 publications

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“…There is no state in the band gap with DFT, consistent with the delocalisation of the oxygen hole. Instead the hole state is found at the top of the VB, which is consistent with earlier findings for other oxides with these oxygen hole polarons [43,45,66,67].…”

Section: Methodssupporting

confidence: 91%

“…This value of U was determined by obtaining the position of the polaron state relative to the VB in Li-doped MgO [43], but can also be found from experimental data [69]. Since U has no effect on the conduction band states, which derive from Ti 3d orbtials, then DFT+U, as used here, cannot give the correct band gap and hence the correct offset of the defect state to the conduction band.…”

Section: Methodsmentioning

confidence: 99%

“…These systems have reduced metal cations, which are localised on two metal centres, but for which DFT delocalises the electrons over all metal centres. Aliovalent doped oxides further highlight the inability of DFT to describe localised states; these include Li-doped MgO [43,44] Al-doped SiO 2 [45,46] and 5 5 La doped CeO 2 [47]. In these examples, the dopant has an oxidation state smaller than the cation it replaces so that oxygen ions near the dopant cannot achieve a closed shell O 2-configuration and instead an O -species with a 2s 2 2p 5 electronic configuration is formed; this oxygen shows features consistent with a polaron -a defect with a localised charge, coupled with a structural distortion.…”

Section: Introductionmentioning

confidence: 99%

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Charge compensation in trivalent cation doped bulk rutile TiO₂

Iwaszuk

Nolan²

2011

J. Phys.: Condens. Matter

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Access to the full text of the published version may require a subscription. analyse the charge compensation process with these dopants. With all dopants, DFT delocalises the oxygen hole polaron that results from substitution of Ti with the lower valent cation. DFT also finds an undistorted geometry and does not produce the characteristic polaron state in the band gap. DFT+U and hybrid DFT both localise the polaron, which is accompanied by a distortion to the structure around the oxygen hole site. DFT+U and HSE06 both give a polaron state in the band gap. The band gap underestimation present in DFT+U means that the offset of the gap state from both the valence and conduction band cannot be properly described, while the hybrid DFT offsets should be correct. We have investigated dopant charge compensation by formation of oxygen vacancies. Due to the large 2 2 number of calculations required, we use DFT+U for these studies. We find that the most stable oxygen vacancy site has either a very small positive formation energy or is negative, so that under typical experimental conditions, anion vacancy formation will compensate the dopant. Rights © 2011 IOP Publishing Ltd. This is an author-created, uncopyedited version of an article accepted for publication in Journal

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Section: Methodssupporting

confidence: 91%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Charge compensation in trivalent cation doped bulk rutile TiO₂

Iwaszuk

Nolan²

2011

J. Phys.: Condens. Matter

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“…In this work, we applied a Hubbard U to the Ti 3d states (U = 4.5 eV, commonly used) and to the O 2p states (U = 7 eV [69,70] ) since refs [69,70,71] show that GGA-DFT cannot describe the nature of the oxygen hole state. showing the local geometry around the dopant, the electronic density of states projected onto the O 2p states of TiO2 and the excess spin density (which is the difference between the number of spin up and spin down electrons, which in this case is 1) for each dopant.…”

Section: Density Functional Theory Simulations Of Tio2 Doping: Some Dmentioning

confidence: 99%

Design of Novel Visible Light Active Photocatalyst Materials: Surface Modified TiO₂

et al. 2016

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Type of publicationArticle (peer-reviewed) AbstractThis progress review describes our work on the design of new TiO2 based photocatalysts. The key concept is the formation of composite structures through the modification of anatase and rutile TiO2 with molecular-sized nanoclusters of metals oxides. Our density functional theory (DFT) level simulations have been compared with experimental work synthesizing and characterizing surface modified TiO2. We use DFT to show that nanoclusters of metal oxides such as TiO2, SnO/SnO2, PbO/PbO2, ZnO and CuO are stable when adsorbed at rutile and anatase surfaces and can lead to a significant red shift in the absorption edge which will induce visible light absorption; this is the first requirement for a useful photocatalyst. We determine the origin of the red shift and the fate of excited electrons and holes. For p-block metal oxides the oxidation state of Sn and Pb can be used to modify the magnitude of the red shift and its mechanism. We describe comparisons of recent experimental studies of surface modified TiO2 that validate our DFT simulations. These nanocluster-modified TiO2 structures 2 form the basis of a new class of photocatalysts which will be useful in oxidation reactions and with a correct choice of nanocluster modified can be applied to other reactions.

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“…The spin density is defined as the difference in the electron density of up and down electron spin densities. 29,30 Additionally the cohesive energy (E coh ) of each model system was calculated. It is defined as the energy required for breaking the system into the isolated atomic species.…”

Section: Methods and Calculationsmentioning

confidence: 99%

Effects of N doping on the electronic properties of a small carbon atomic chain with distinctsp2terminations: A first-principles study

et al. 2011

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Carbon nanostructures consisting of corannulene/coronene-like pieces connected by atomic chains and doped with nitrogen atoms have been addressed by carrying out first-principles calculations within the framework of the spin-polarized density functional theory. Our results show that the conformation, charge distributions, and spin states are significantly influenced by the nitrogen incorporation in comparison to these characteristics of similar pure carbon structures. Higher concentration of incorporated nitrogen leads to a smaller highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap and different conductive states near the Fermi level. In turn the different location of the N-incorporation sites allows switching on and off of the π -electron magnetism in these systems. We found that the rotational deformation of the terminations with respect to the carbon chain depends on the number and the location of the incorporated N atoms. The most stable N-doped structures exhibit a relative rotation of the terminations of approximately 90 degrees. These findings indicate that by controllable N doping one can tune the conducting channel of carbon chains connected to sp 2 terminations; thus obtaining low band-gap nano-units.

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The electronic structure of alkali doped alkaline earth metal oxides: Li doping of MgO studied with DFT-GGA and GGA+U

Cited by 69 publications

References 31 publications

Charge compensation in trivalent cation doped bulk rutile TiO₂

Charge compensation in trivalent cation doped bulk rutile TiO₂

Design of Novel Visible Light Active Photocatalyst Materials: Surface Modified TiO₂

Effects of N doping on the electronic properties of a small carbon atomic chain with distinctsp2terminations: A first-principles study

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The electronic structure of alkali doped alkaline earth metal oxides: Li doping of MgO studied with DFT-GGA and GGA+U

Cited by 69 publications

References 31 publications

Charge compensation in trivalent cation doped bulk rutile TiO2

Charge compensation in trivalent cation doped bulk rutile TiO2

Design of Novel Visible Light Active Photocatalyst Materials: Surface Modified TiO2

Effects of N doping on the electronic properties of a small carbon atomic chain with distinctsp2terminations: A first-principles study

Contact Info

Product

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Charge compensation in trivalent cation doped bulk rutile TiO₂

Charge compensation in trivalent cation doped bulk rutile TiO₂

Design of Novel Visible Light Active Photocatalyst Materials: Surface Modified TiO₂