Computational Investigations of Metal Oxide Surfaces - Metallic Systems: A Quantum Chemist's Perspective - page 205

studies.to.current.applications,.and.also.detail.Fe 2 O 3 .hematite.surface.calculations..
How. experiment. and. theory. have. worked. together. to. elucidate. the. appropriate.
.surface.structure.will.also.be.described..We.then.provide,.in.Section.7.3,.an.over-
view.of.several.current.applications.of.density.functional.calculations.to.pertinent.
technological. and. scientiic. metal. oxide. questions.. We. conclude. by. emphasizing.
some.of.the.remaining.challenges.facing.the.theoretical.and.computational.studies.
of.metal.oxide.surfaces.

7.2 APPLICATIONS OF DFT TO AL 2 O 3 AND FE 2 O 3
7.2.1 a lumina c alculationS
In.the.1990s,.density.functional.implementations.and.computing.power.had.reached.
the.stage.where.a.variety.of.metal.oxide.surfaces.were.tractable..Alumina.Al 2 O 3 .is.an.
important.material.for.many.applications.ranging.from.use.as.a.high-k.dielectric,.to.
a.component.in.thermal.barrier.coatings,.to.a.support.in.
heterogeneous.catalysis..The.α-Al 2 O 3 .phase.was.studied.
early.due.to.its.stability.as.well.as.its.symmetry.result-
ing.in.a.reasonable.number.of.atoms.in.a.computational.
supercell. (10. atoms. in. the. rhombohedral. unit. or. 30.
atoms.in.the.full.hexagonal.cell.for.the.space group.167,.
R3

C

_

c ,. relative. to. ∼100. atoms. in. the. metastable. gamma.
phase.).Figure.7.2.displays.a.side.view.of.the.corundum.
structure.with.oxygen.positions.shown.in.red.and.metal.
ions.in.blue.
Early. calculations. of. alumina. surfaces. focused.
on. clean. stoichiometric. surface. terminations. for. this.
phase. 17-19 .In.1999,.a.study.by.Batyrev.et.al. 20 .explored.
the.atomic.and.electronic.structure.of.α-Al 2 O 3 .using.peri-
odic.density.functional.calculations.within.a.planewave.
pseudopotential. implementation.. They. explored. ive.
different.surface.terminations.with.varying.excess.oxy-
gen. terminations. in. an. attempt. to. explore. the. impact.
of. oxygen. pressure. on. the. favorability. of. a. particular.
surface.termination.for.the.basal.plane..They.found.the.
stoichiometric.aluminum.surface.termination.to.be.the.
most.energetically.favorable.of.the.surfaces.studied.over.
a. signiicant. range. of. oxygen. partial. pressures,. further.
reinforcing.the.validity.of.the.surface.termination.cho-
sen.in.the.earlier.study.by.Manassidis.et.al. 17 .Wang.et.al..
showed.that.stable.surface.terminations.of.oxygen.were.
accessible.only.in.the.presence.of.hydrogen.and.helped.
resolve. differences. between. theoretically. and. experi-
mentally.predicted.surface.relaxations. 21 .These.ab.initio.
thermodynamics. studies,. whereby. surface. energies.
are. calculated. in. DFT. and. then. expressed. in. terms. of.

B O A

FIGURE 7.2 Side. view.
of. the. corundum. struc-
ture. for. α-Al 2 O 3 . as. well.
as. hematite.. The. oxygen.
positions. are. shown. in. red.
with.the.metal.ion.positions.
displayed. in. blue.. Possible.
cleavage. locations. for. the.
(0001). basal. plane. for. this.
crystal.will.be.discussed.in.
the.text.