Density Functional Theory Calculations on Cobalt and Platinum Transition Metal Clusters - Metallic Systems: A Quantum Chemist's Perspective - page 346

or.subtraction.of.a.single.atom.or.even.a.single.electron,.we.discuss.the.current.state.
of. understanding. of. geometric,. electronic,. and. magnetic. properties. of. neutral. and.
anionic.small.cobalt.clusters,.and.the.effect.of.spin-orbit.(SO).coupling.on.chemical.
and.physical.properties.of.small.platinum.clusters.
10.2 STRUCTURAL, ELECTRONIC, AND MAGNETIC PROPERTIES
OF NEUTRAL AND ANIONIC SMALL COBALT CLUSTERS
Co. clusters. are. one. of. the. most. interesting. examples. of. TMCs. due. to. their. mag-
netic.properties.[48].and.importance.in.magnetic.storage.devices..Although.it.was.
reported.by.a.photoionization.experiment.[49].that.Ni n .and.Co n .clusters.consisting.
of.50-800.atoms.have.icosahedral.structures,.the.structures.of.smaller.Co n .( n .≤.50).
clusters.were.not.well.identiied..Similarly,.chemical.reactions.of.Co n .with.water.and.
ammonia.[50].indicate.icosahedral.structures.for.both.bare.and.ammoniated.cluster.
in.the.size.range.of. n = 50-100..However,.it.was.also.mentioned.that.small,.bare.clus-
ters.may.adopt.a.variety.of.structures.[51]..Yoshida.et.al..[52].obtained.the.geometry.
and.electronic.structures.of.Co − .anions.( n = 3,.4,.and.6).by.comparing.the.measured.
and. calculated. photoelectron. spectra.. The. magnetic. moments. and. adiabatic. mag-
netization. of. bare. Co n . clusters. (20.≤. n .≤.300). were. investigated. via. Stern-Gerlach.
experiments.by.different.groups.[48,53]..They.found.that.the.magnetic.moment.per.
atom. for. small. Co n . clusters. are. signiicantly. larger. than. the. reported. bulk. value.
(1.7.μ B .[54]).
Theoretical.investigations.of.cobalt.clusters.include.an.evolutive.algorithm.based.
on.the.semiempirical.Gupta.potential.[55],.tight-binding.molecular.dynamics.[56],.
and.pseudo-atomic.[57-61].and.all-electron.DFT.calculations.[62-65]..Results.in.the.
literature.are.not.in.good.agreement.with.each.other..The.discrepancies.among.DFT.
calculations.may.be.attributed.to.differing.basis.sets.and.exchange-correlation.(xc).
functionals.and.the.incomplete.searches.for.the.global.minimum..Due.to.the.scar-
city.of.experimental.study,.these.inconsistencies.still.remain.unresolved..We.are.not.
aware.of.any.higher.level.non-DFT.work.for.these.clusters.
10.2.1 c omPutational d etailS
We.performed.[66].DFT.calculations.for.Co n .clusters.( n .≤.6).within.the.generalized.
gradient.approximation.(GGA).to.investigate.the.putative.ground.state.by.relaxing.
geometric. structures. starting. from. a. large. number. of. initial. candidate. geometries.
including. those. reported. in. the. literature. [57-65]. for. a. large. number. of. different.
spin. multiplicities.. The. NWChem. 5.0. program. package. [67]. was. used. to. perform.
geometry.optimizations.and.total.energy.calculations..The.CRENBL.[68].basis.set.
and.effective.core.potential.(ECP).for.Co.were.employed.whereby.the.outermost.17.
electrons.of.the.free.Co.atom.(3s 2 3p 6 3d 7 4s 2 ).were.treated.as.valence.electrons..The.
GGA.exchange.functional.of.Becke.[69].and.the.correlation.[70].functional.of.Lee,.
Yang,.and.Parr.(BLYP).were.used.to.compute.the.PES..Geometries.were.optimized.
without.imposing.any.symmetry.constraints..Spin-polarized.calculations.were.per-
formed.for.the.irst.3 n .+.1.spin.multiplicities,.where. n .is.the.number.of.atoms.in.the.
clusters.