Chemistry Reference
In-Depth Information
9.6. Reactions....................................................................................................... 322
9.6.1. Formation.of.Benzene.from.Acetylene.on.Small.(
n
.=.1-4).Fe.
Clusters.............................................................................................. 322
9.6.2. Oxidation.of.CO.with.Cationic.Iron.Oxide.Clusters......................... 329
9.7. Concluding.Remarks.and.Perspectives......................................................... 333
References.............................................................................................................. 334
9.1 INTRODUCTION
A.wide.variety.of.systems,.properties,.concepts,.and.perspectives.lie.within.the.scope.
of.this.volume.on.
Metallic Systems: A Quantum Chemist's Perspective
..Of.course,.
there. is. no. single. “quantum. chemist's. perspective.”. To. some,. a. “metallic. system”.
implies.typical.bulk.metallic.properties,.electrical.conductivity,.thermal.conductiv-
ity,.and.the.like..To.others,.the.presence.of.a.single.metal.atom.in.a.molecule.or.com-
plex.is.satisfactory.for.its.classiication.as.a.“metallic.system.”.In.between,.one.inds.
the. fascinating. world. of. metal. clusters. with. properties. that. are. sometimes. impor-
tantly. similar. to. those. of. the. bulk. metal. and. sometimes. crucially. different.. Both.
perspectives.have.value..Metal.clusters.have.their.own.special.properties,.depending,.
for.example,.on.cluster.size,.and.there.is.a.clear.interest.in.taking.advantage.of.them.
to.tune.the.performance.for.a.particular.application,.for.example,.catalysis..On.the.
other.hand,.one.can.use.clusters.as.models.for.either.bulk.systems.or.larger.nano-.and.
micro-clusters.such.as.those.present.in.working.catalysts..Of.course,.the.quality.of.
the.model.will.depend.crucially.on.the.size.of.the.cluster.
This. chapter. will. look. at. metal. clusters. from. the. particular. perspective. of. ive.
quantum.chemists.who,.over.the.years,.have.studied.a.variety.of.metal.clusters.using.
density.functional.theory.(DFT).as.their.primary.methodology.(indeed.a.“metallic.
system,”. the. homogeneous. electron. gas,. lies. at. the. heart. of. the. early. development.
of.DFT)..A.wide.variety.of.metals.will.be.discussed:.alkalis,.free-electron.metals,.
noble. metals,. and. transition. metals. (TMs).. We. will. also. discuss. a. wide. variety. of.
properties:.electronic.structure,.spectroscopies.of.various.types,.geometrical.struc-
ture,.vibrations,.dynamics,.reactivity,.and.reactions..The.computational.demands.for.
both.accuracy.and.speed.vary.widely.depending.on.the.type.of.metal.and.the.prop-
erty.of.interest.
The.performance.of.various.DFT.techniques.has.improved.greatly.over.the.years,.
and.we.will.try.to.give.the.reader.a.sense.of.this.progress.through.brief.descriptions.
of.and.references.to.the.methodological.principle.and.software.advances.that.have.
been.made,.from.the.Xα.scattered-wave.method.to.linear.combination.of.Gaussian-
type.orbitals-Xα.(LCGTO-Xα),.to.the.use.of.local.density.functionals.in.early.ver-
sions.of.the.software.package.deMon,.and,.inally,.to.the.current.version.deMon2k,.
which. incorporates. the. latest. generalized. gradient. approximations. (GGAs). and.
meta-GGA.functionals..While.the.historical.perspective.is,.we.think,.both.interest-
ing. and. important,. the. chapter. will. focus. primarily. on. present. capabilities,. recent.
applications,. and. future. perspectives.. This. overview. will. be. rather. personal. and.
focused.on.the.development.and.applications.of.deMon;.other.chapters.will.provide.
the.perspective.of.researchers.using.other.software.
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