（様式第 20）成果報告書

共同利用（産業利用トライアルユース：先端研究施設共用促進事業 『みんなのスパコン』TSUBAME によるペタスケールへの飛翔） 成果報告書 平成 ２０ 年度 課題種別 「新規材料開発のための、オーダーＮ法による金属酸化物表面の第一原理シミュレーション」
利用課題名 新規材料開発のための、オーダーＮ法による金属酸化物表面の第一原理シミュレーション
英文：The order-N first-principles simulation of metal oxide surfaces for novel material development.
利用課題責任者
Kosuke Doga所属
Accelrys K.K.
www.accelrys.co.jp

邦文抄録（300 字程度）

遷移金属酸化物は触媒や塗料、電子デバイス等の開発において、非常に重要な役割を果たしている。遷移金属酸化物における研究課題の一つとして、触媒反応の活性と選択性における表面欠陥の影響が重要視されている。遷移金属酸化物の表面酸素欠陥はホストの系に対して構造および電子状態の変化を引き起こす。
今回の利用においてはこれらの系に対するコンピューターシミュレーション技法を検討するために、非常に良く知られている酸化アルミニウムの系において点欠陥を持つモデルを構築、オーダー N法のDFT計算手法であるONETEPでシミュレーションを実行、結果の検証を行った。また、酸化ガリウム、酸化インジウムの系においても予備的な計算を行った。
英文抄録（100 words 程度）

Transition metal (TM) oxides are of great importance for heterogeneous catalysis, corrosion-protective coating of
metals and microelectronic devices. An important issue in TM oxide-based material is the role of surface defects
to the activity and selectivity of the catalyst. Oxygen vacancies at (TM) oxide surfaces (or in the bulk) alter thegeometric and electronic structure of the host system. In the present study the oxygen vacancy scenarios wasdescribed for aluminum oxide, Gallium oxide and Indium oxide using ONETEP (Order-N Electronic Total EnergyPackage) a parallel density-functional theory code for large-scale first-principles quantum-mechanicalcalculations.
Keywords: ONETEP, oxide, vacancy, selectivity, catalysis, Order-N

背景と目的

microscopic) of these defects will help to elucidate the effectTransition metal (TM) oxides constitute an important class ofthat they have on the system’s functionality has been theinorganic solids exhibiting a very wide variety of structures anddriving force for pursuing experimental and theoretical research

electronic and magnetic properties that are due to the nature ofon reduced materials. Point defects in TM oxides such as

the outer d states. They are of great importance for a number ofvacancies and interstitials account for the transport properties

a technological applications such as heterogeneous catalysis,of ionic solids.The study of aluminum oxides is motivated bycorrosion-protective coating of metals and microelectronic

fundamental scientific interest as well as by their technologicaldevices. Furthermore, bulk defects play a significant role inrelevance, e.g., as support in heterogeneous catalysis. An important

determining surface properties where, for example, annealingrole in enhancing catalytic reactions is believed to be played by

to high temperatures is necessary. In turn, the host system will

structural defects, in particular, oxygen vacancies, which act aslargely determine the properties of the vacancies. The

adsorption centers for molecules or metallic clusters [1, 2].

expectation

Atomic-scale studies of such vacancies are exceedingly difficult,thata

fundamentalunderstanding(i.e.,

（様式第 20）成果報告書
since insulating bulk oxides cannot be probed by many

selected adsorbates on reduced surfaces and the nature ofexperimental techniques, such as scanning tunneling microscopy

reaction intermediates on easily reducible oxides. In this study(STM). A way to circumvent this problem is to study ultrathin

we aim to look into the stability of the structure with vacancy

oxide films grown on conducting substrates. Because of theconcentration for TM and RE oxide, so far we are able to lookstructural complexity of these films, the microscopic interpretation

into Al2O3, Ga2O3 and InO2of experimental data remains a challenge.
ONETEP is an ab initio electronic structure package for totalenergy calculations within density-functional theory. It combines

結果および考察‘linear scaling’; in that the total computational effort scales only

In the present case we have tried to optimize different vacancy

linearly with system size, with ‘plane-wave’ accuracy, in that theconcentration in alpha alumina to propose a correlation to theconvergence of the total energy is systematically improvable in thevacancy concentration and activity through the formation energy.

manner typical of conventional plane-wave pseudopotential
methods. ONETEP was developed from the beginning as a parallelcode [3, 4].We present recent progress on improving theperformance, and thus in effect the feasible scope and scale, ofcalculations with ONETEP on parallel computers comprising large
clusters of commodity servers. Our recent improvements makeComposition: O324Al216

Composition: O318Al216

calculations of tens of thousands of atoms feasible, even on fewer
than 100 cores. Efficient scaling with number of atoms and number

We have also calculated indium oxide without defect.

of cores is demonstrated up to 32,768 atoms on 64 cores.

概要
Oxygen vacancies have been detected and investigated using avariety of spectroscopic techniques; however, much has beenlearned recently about the structure of defective surfaces using
scanning probe techniques. In spite of that, there are still
difficulties

intheexperimental

determination

of

the

InO2 without defectvacancy-induced lattice relaxations, and information about thevacancy formation energy (hence defect stability) is not always

CASTEP density of stateexperimentally obtainable. Therefore, a great number oftheoretical studies on oxygen removal from TM and RE oxides
have appeared in the literature. In particular, isolated oxygen
vacancies at differently oriented surfaces and in the bulk havereceived much attention. Strong interactions can occur between
defects, causing them to cluster or order. Yet, isolated defects(or a low concentration of them) have been the natural starting
point for the theoretical studies. Once a more accurate
description of the surface electronic structure has been reached,
the next logical step would be to re-inspect results of surface
chemistry studies on TM and RE oxides, e.g., on the binding ofONETEP density of state（様式第 20）成果報告書

We calculated density of states of aluminum oxide with ONETEP
and the well validated DFT tool, CASTEP[5]. Keeping the band

Table 2: Calculated energy formation of surface oxygen vacancies

gap same ONETEP will allow one to see the distribution of bands

in Alpha-Al2O3 (0001). The oxygen vacancy in the second or fifthin more detail. An appalling fact is the band distribution in thelayer is denoted by layer 2 and layer 5, respectively.

Indium oxide and it is certain that there will be more influence ofvacancy in the band architecture.
The point is to see the activity at the defect or vacancy site afteroptimization.

All calculations were performed with ONETEP

with SINC basis function with 800 eV cut off and a force
convergence of 0.0001 eV/angstrom and a stress convergence of0.001 GP1.
Same calculation is repeated for Ga2O3, the interest here si tocompare the behavior of the material with alumina and Indium
oxide. We have shown a simpler HOMO trend for Ga and thedistribution looks very uniform without defect.

Ga2O3
Now look closely in the defect and wanted to compare the defectconcentration with the formation energy and a swell the localized
distortion of the lattice.

Chosen HOMO

Table 1: Internal relaxation both with position and percentage
with change in the layer location

（様式第 20）成果報告書

まとめ、今後の課題
We have performed the defect concentration variation forAlumina with 2, 4 and 6 Oxygen vacancy per 560 atoms.
This is to compare the formation energy of the vacancy and its
relative stability, with that result the next step will be to see theadsorption of metal cluster to see the stability and hence thecatalytic activity.

With Ga2O3 and InO2 the initial structure

optimization with their relate properties were calculated wewish to do the similar concentration of vacancy concentration
study with these tow oxides followed by the adsorption energy
Electron densityof related metal clusters to correlate the activity.

We consider the energy formation of Al vacancies in the bulk andThe aluminum vacancy results is very new in terms of vacancy

in the Al-terminated surface for super cell with 560 atoms. Allconcentration and we need to perform the adsorption energycalculations were performed with TSUBAME 16 cores.

calculation or and the vacancy formation energy for other TM

For the unrelaxed alpha-alumina, the cost to remove a neutral Aloxides.

atom is of 16.83 eV, allowing the 6 nearest anions to relax drops
this energy to 15.91 eV. Further relaxation up to 16, 58, or 89

This work has been done by Abhijit Chatterjee, Principal

atoms around the Al vacancy has only a minor effect since theScientist of Accelrys K.K.

energy formation decreases to 15.63, 15.51, and 15.49 eV,
respectively. As in the case of the oxygen vacancy, the larger
relaxation effect occurs for the nearest-neighbor ions, which in thiscase relax roughly by 7%–8% ~Table 2. However, for the bulk
neutral Al vacancy, the second nearest-neighbor relaxation is alsosignificant, 4%. In the case of the surface Al vacancy, the energy
formation for the unrelaxed substrate, calculated with respect to thecorresponding relaxed clean surface, is 14.95 eV.

Reference:
1. E. Wahlstro¨m et al., Phys. Rev. Lett. 90, 026101 (2003).
2. M. Ba¨umer and H.-J. Freund, Prog. Surf. Sci. 61, 127 (1999_
3. C.-K. Skylaris, P.D. Haynes, A.A. Mostofi, M.C. Payne, Phys.
Stat. Sol. B 243 (2006) 973.
4. N. D. M. Hine, P. D. Haynes, A. A. Mostofi, and M. C. Payne
J. Chem. Phys. 133, 114111 (2010);
5. Milman, V., Winkler, V., White, J. A., Pickard, C. J, Payne,
M. C.,Akhmatskaya, E. V., and R. H. Nobes, Int. Quant. Chem.,
2000, 77, 895.