Density Functional Calculations of Metal Clusters: Structure, Dynamics, and Reactivity - Metallic Systems: A Quantum Chemist's Perspective - page 303

Ni 2 Ni 3

Ni 4 Ni 5

FIGURE 9.13 Different. topologies. considered. as. initial. structures. for. the. geometry. opti-
mization. of. Ni n ,. Ni n + ,. and. Ni n − . ( n .=.2-5). clusters.. (Reprinted. from. Lopez. Arvizu,. G.. et. al.,.
J. Chem. Phys .,.126(19),.May.21,.194102-1,.2007..With.permission.)

as.well.[146]..The.calculated.values.were.compared.with.available.data.from.the.lit-
erature..The.GGA.basis.sets.employed.turn.out.to.be.very.important.for.the.correct.
ground-state.structure.determination.of.nickel.clusters..Full.geometry.optimizations.
were.performed.considering.as.initial.structures.the.different.topologies.illustrated.
in.Figure.9.13.
In. Figures. 9.14. and. 9.15,. the. results. of. the. LDA. and. GGA. geometry. optimiza-
tions,.structures,.bond.lengths.in.Å,.and.multiplicities.of.the.ground.states.of.neutral,.
cationic,.and.anionic.nickel.clusters.are.presented.
The.calculations.of.the.clusters.reported.in.Figure.9.14.have.been.performed.with.
the.original.DZVP-LDA.basis.set.as.well.as.with.the.newly.developed.DZVP-GGA.
and.TZVP-GGA.basis.sets.in.combination.with.the.VWN.functional..The.DZVP-
LDA.bond.lengths.are.given.without.parentheses.while.the.bond.lengths.obtained.
with. the. DZVP-GGA. and. TZVP-GGA. basis. sets. are. given. in. round. and. square.
brackets,.respectively..The.results.displayed.in.Figure.9.15.have.been.obtained.with.
the.newly.developed.DZVP-GGA.and.TZVP-GGA.basis.sets.in.combination.with.
the.PW86.functional.
A.comparison.of.Figures.9.14.and.9.15.shows.that.depending.on.the.methodology.
used,.structural.changes.in.the.clusters.may.occur.as.in.the.case.of.the.nickel.trimer.
and. of. the. nickel. pentamer.. In. fact,. for. Ni 3 − ,. the. VWN. functional. in. combination.
with.all.employed.basis.sets.predicts.a.distorted.triangular.structure.(Figure.9.14),.
whereas.with.the.newly.developed.DZVP-GGA.and.TZVP-GGA.basis.sets.in.com-
bination.with.the.PW86.functional,.an.almost.linear.ground-state.structure.is.found.
(Figure. 9.15).. This. was. the. irst. time. that. such. a. structure. was. predicted. for. the.
anionic.nickel.trimer.[146]..The.angle.formed.by.the.three.Ni.atoms.is.around.165°.
In.order.to.gain.more.insight.into.the.nickel.trimer.ground.states,.the.orbital.ill-
ing. pattern. with. increasing. charge. of. the. cluster. was. investigated.. In. Figures. 9.16.
and.9.17,.the.schematic.correlation.diagrams.of.the.Kohn-Sham.MOs.between.cat-
ionic.and.neutral.Ni 3 .clusters.and.between.neutral.and.anionic.trimers.are.presented,.