Density Functional Calculations of Metal Clusters: Structure, Dynamics, and Reactivity - Metallic Systems: A Quantum Chemist's Perspective - page 333

( 4 O 2 Fe 2 O + )

0

-0.21

0.00

-0.34 4 Fe 2 O +

2 Fe 2 O +

- 3 O 2

+ 1 CO

4 Fe 2 O 4 +

-1.56

-2.03

-2

4 O 2 Fe 2 O +

- 1 CO 2

+ 1 CO

-3.26

4 Fe 2 O 5 CO +

-4

4 Fe 2 O +

-4.70

- 1 CO 2

-5.22

4 Fe 2 O 4 CO +

-6

+ 1 CO

-8

-7.78

2 Fe 2 O 3 CO +

+ .and.CO..

FIGURE 9.34 (See color insert.) Reaction.proile.of.the.reaction.between. Fe O

2 5

Relative.energies.are.given.with.respect.to.the.reactant. Fe O
2

+ .in.eV..The.arrows.in.the.blue.
Fe.atoms.indicate.spin.broken.solutions..(Reprinted.from.Reilly,.N..et al.,. J. Phys. Chem. C ,.
111(51),.December.1,.19086,.2007..With.permission.)

5

occurs. in. the. reaction. of. CO. with. Fe O
2

+ .. Similar. results. are. obtained. for. higher.

5

iron.oxides,.too.[220].

9.7 CONCLUDING REMARKS AND PERSPECTIVES
This.chapter.has.taken.a.rather.personal.view.of.metallic.systems,.focusing.on.recent.
technical.improvements.to.the.deMon2k.software.and.giving.some.examples.from.
our.own.work.in.the.area.of.metal.clusters..The.examples.are,.for.the.most.part,.small.
to.very.small.clusters..Indeed,.for.TMs,.already.at.three.or.four.atoms,.the.challenges.
are.substantial..Alkali.and.noble.metals.are.considerably.more.forgiving;.but,.even.
for.these,.the.task.of.locating.all.of.the.possible.local.minima,.and.calculating.rel-
evant.properties,.remains.in.the.nonroutine.category.
Progress. over. the. last. decade. has. been. substantial.. Almost. all. of. the. examples.
treated.here.could.not.have.been.done.only.a.few.years.ago,.at.least.not.with.pres-
ent.day.eficiency.and.ease..Structures.can.now.be.optimized.and.transition.states.
located,. thanks. to. the. eficient. implementation. of. rigorous. state-of-the-art. algo-
rithms..Vibrational.analysis.is.now,.for.the.most.part,.routine,.notwithstanding.the.
usual.dificulties.with.imaginary.frequency.modes.that.can.arise.in.metal.clusters.
when. there. are. a. number. of. competing. structures. with. close-lying. excited. states..
In. such. cases,. spin. contamination. must. be. considered,. too.. The. cases. of. V 3 ,. V 3 O,.
and.Nb 3 O.provided.compelling.examples.of.the.power.of.combining.experimental.
data.with.computations,.yielding.deinitive.ground-state.assignments..The.accurate.