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electronic.and.geometric.structure.of.these.systems.was.the.subject.of.several.DFT.
investigations.in.the.last.10.years.or.so,.and.it.would.not.be.appropriate.to.review.
all.of.them.here.
Among.all.the.available.works.on.iron.systems,.those.published.by.Salahub.and.
Chrétien.[198].and.Gutsev.and.Bauschlicher.[199].are.particularly.interesting..Both.
works.present.results.of.extensive.studies.performed.on.neutral,.cationic,.and.anionic.
small.iron.clusters,.concluding.that.the.determination.of.the.ground-state.structure.
of.small.iron.clusters.depends.on.the.choice.of.the.correlation.functional.
Despite.the.fact.that.many.works.on.these.systems.are.available,.additional.exper-
imental. information. is. required. in. order. to. unequivocally. assign. the. ground-state.
structure.of.small.iron.clusters.
Since.the.static.polarizability.is.a.property.directly.related.to.the.electronic.prop-
erties. of. clusters,. polarizability. measurements. would. be. highly. valuable. in. deini-
tively.answering.questions.about.the.electronic.structure.of.these.systems..However,.
no.experimental.studies.on.the.electric.properties.of.these.small-sized.systems.are.
available.. Therefore,. we. carried. out. theoretical. studies. on. the. static. polarizability.
of.small.iron.and.nickel.clusters.in.order.to.gain.more.insight.into.their.electronic.
structure.and.to.guide.future.experimental.investigations.[200,201]..For.both,.iron.
and.nickel.atoms,.newly.developed.basis.sets.were.employed.for.the.polarizabilitiy.
calculations.. For. these. calculations,. the. inite. ield. approach. of. Kurtz. et. al.. [202].
implemented.in.the.deMon2k.code.was.used..The.reliability.of.this.approach. was.
extensively.tested.for.various.systems.[192,193,203-207],.including.sodium.and.cop-
per.clusters.as.well.as.iron-containing.molecules..These.studies.demonstrated.that.
DFT.methods.can.be.used.in.order.to.predict.fairly.accurate.polarizability.values.for.
metallic.and.TM.systems..In.Figure.9.26,.the.mean.polarizability.per.atom.(in.a.u.).
of.the.studied.iron.clusters.up.to.the.tetramer.is.plotted.
As.Figure.9.26.shows,.going.from.the.atom.up.to.the.tetramer,.the.mean.polariz-
ability.per.atom.has.an.oscillating.behavior..The.comparison.of.this.plot.with.those.
of. Figures. 9.23. through. 9.25. shows. that. the. calculated. polarizability. per. atom. of.
small.iron.clusters,.going.from.the.atom.to.the.tetramer,.presents.the.same.trend.as.
that. experimentally. observed. by. Knight. et. al.. [188]. for. sodium. clusters.. However,.
70
Fe-(PW86)
60
50
40
1
2
3
4
Number of iron atoms
FIGURE 9.26
Mean.polarizability.per.atom.of.Fe
n
.(
n
.=.1-4).
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