Exploring the Borderland between Physics and Chemistry: Theoretical Methods in the Study of Atomic Clusters - Metallic Systems: A Quantum Chemist's Perspective - page 386

function. isosurfaces. and. their. condensed. values. over. the. basins. are. also. shown..
They.are.calculated.as.the.integral.of.the.Fukui.function.over.the.respective.volume..
Larger.numbers.indicate.more.reactive.regions..Therefore,.one.expects.that.a.hydro-
gen. atom. would. bind. the. cluster. in. the. zone. where. the. condensed. Fukui. function.
has.the.largest.value..In.fact,.in.Ref..[53].it.was.found.that.the.predicted.cluster.was.
always.one.of.the.most.stable.ones..Exceptions.occur.when.the.hydrogenated.cluster.
drastically.alters.the.Si n .skeleton.of.the.Si n H.cluster.with.respect.to.the.initial.silicon.
cluster..A.similar.methodology.has.also.been.used.to.explain.and.predict.the.reactiv-
ity.of.copper.clusters.with.molecular.oxygen.[56].
11.5 UNIQUE PHYSICAL PROPERTIES OF CLUSTERS
AND THEIR RELATION TO THE CORRESPONDING
SURFACE AND BULK PROPERTIES
As. mentioned. above,. atomic. clusters. show. many. distinct. properties. from. those. of.
isolated. atoms. or. bulk. solids. that. can. be. very. useful. in. practical. applications.. At.
the. same. time,. there. is. the. possibility. to. analyze. known. phenomena. from. a. new.
perspective..For.example,.the.discovery.of.giant.plasmon.resonances.in.metal.clus-
ters.[57,58].and.in.fullerenes.[59,60].allowed.scientists.to.study.the.transition.from.
the.classical.Mie.picture.of.plasmon.oscillations.to.the.quantum.limit.or.to.detect.
cluster.deformations.by.the.value.of.the.splitting.of.plasmon.resonance.frequencies.
[3,.and.references.therein]..In.this.section,.we.briely.discuss.another.very.interest-
ing.phenomenon:.the.onset.of.magnetism.in.bare.and.ligand-coated.clusters.of.gold,.
a. typical. diamagnetic. metal.. We. emphasize. the. usefulness. of. clusters. as. “transi-
tion.structures”.that.facilitate.a.better.understanding.of.magnetism.in.molecular.and.
extended.systems.(surfaces.or.solids).
One.of.the.irst.observations.of.magnetism.in.gold.was.reported.by.Zhang.and.
Sham.[61].in.their.x-ray.spectroscopic.study.of.alkane-thiolated.nanoclusters..Later,.
Crespo.et.al..[62].used.x-ray.absorption.near-edge.structure.measurements.to.show.
the.appearance.of.ferromagnetism.accompanied.by.room-temperature.hysteresis.in.
thiol-capped.Au.nanoparticles.with.a.diameter.of.1.4.nm..This.rather.surprising.ind-
ing.led.to.the.proposal.that.the.strong.chemisorption.of.ligands.into.relatively.small.
nanoparticles.of.bulk.diamagnetic.materials.could.induce.permanent.magnetism.as.a.
result.of.electronic.structure.effects.involving.interactions.between.the.sp-orbitals.of.
the.adsorbate.and.the.5d-orbitals.of.the.Au.atoms.lying.on.the.surface.of.the.nanopar-
ticle.. This. mechanism. was. later. questioned. by. the. results. reported. by. Hori. et. al..
[63].based.on.superconducting.quantum.interference.device.magnetometer.(SQUID).
measurements.of.a.series.of.Au.nanoparticles.protected.by.strongly.interacting.thiols.
such.as.dodecane.thiol.(DT).and.weakly.coupled.ligands.such.as.polyacrylonitrile.
(PAN),.polyallyl.amine.hydrochloride.(PAAHC),.and.polyvinyl.pyrrolidone.(PVP)..
In.this.study,.the.authors.found.that.the.strong.chemisorptive.interaction.between.the.
sulfur.atom.in.DT.and.the.Au.atoms.on.the.surface.of.the.nanoparticle.induced.a.spin.
singlet.state.that.signiicantly.decreased.the.magnetization.of.the.system.(although.
it.did.not.quench.it.completely).when.compared.to.the.corresponding.magnetization.
measured. in. Au. nanoparticles. capped. with. weakly. coupled. ligands. such. as. PAN,.