Chemistry Reference
In-Depth Information
cross-sectional. areas. (4. times. the. area. and. 16. times. the. area).. These. simulations.
show.that.although.the.strengths.of.the.peaks.in.the.density.proile.are.damped.when.
larger.cross-sectional.areas.are.considered,.their.positions.are.unaffected..The.rela-
tive.heights.of.the.peaks.in.the.classical.simulations.differ.from.those.in.the.ab.initio.
simulations,. in. that. in. the. classical. simulations. the. outermost. peaks. are. lower. in.
height.than.the.inner.peaks,.while.in.the.ab.initio.simulations.the.outermost.peaks.
are.of.the.same.or.greater.height.than.the.inner.peaks..The.larger.height.of.the.outer-
most.peaks.in.the.ab.initio.simulations.is.consistent.with.the.idea.that.the.surface.is.
more.strongly.conined.in.the.eDFT.treatment.
5.3.3.2  Introducing a Thin Rigid Wall into Liquid Sodium
As.we.have.noted,.at.the.free.surface,.there.is.a.rapid.decay.of.the.electronic.den-
sity. from. the. bulk. liquid. part. to. the. vapor. region. (where. the. electronic. density.
is.close.to.zero)..In.order.to.probe.the.importance.of.this.on.the.layering,.and.to.
avoid. the. possibility. of. Friedel. oscillations. in. the. electronic. density,. a. computa-
tional.experiment.that.contained.a.rigid.layer.of.atoms,.but.no.vacuum.regions.was.
performed..In.addition.to.considering.the.free.liquid.surface,.molecular.dynamics.
has.been.used.to.consider.the.properties.of.liquid.sodium.interacting.with.a.ixed.
layer. of. sodium. atoms. [73].. In. this. case,. the. charge. density. is. continuous. at. the.
ixed.layer,.meaning.that.there.should.be.no.Friedel.oscillations,.though.the.motion.
of.the.liquid.atoms.is.restricted.by.the.presence.of.the.ixed.layer.of.sodium.atoms..
The. ixed. layer. of. atoms. does. not. represent. a. defect. for. the. electronic. system. in.
the. same. way. as. the. presence. of. a. surface. as. there. is. no. vacuum. region. and. no.
requirement.of.a.rapid.decrease.in.the.electronic.density..Simulations.were.made.
for.liquid.sodium.in.contact.with.a.ixed.layer.of.sodium.atoms.for.temperatures.
of. 400. and. 800.K.. The. density. proiles. for. simulations. performed. at. these. two.
temperatures. are. shown. in. Figure. 5.8.. At. both. of. these. simulation. temperatures,.
strong.layer.formation.in.the.liquid.part.is.shown.by.the.oscillations.in.the.density.
proiles;.the.layer.formation.is.much.stronger.than.for.the.free.surfaces,.suggesting.
a.strong.degree.of.geometrical.coninement.of.the.liquid.part.in.these.systems..It.is.
useful.to.note.that.there.are.no.undercoordinated.liquid.atoms.at.the.interface.with.
(a)
(b)
6.0
4.0
2.0
0.0
0
5
10
15
20
0
5
10
15
20
z (Å)
z (Å)
FIGURE 5.8  Density.proiles.for.simulations.of.liquid.sodium.in.contact.with.a.rigid.ixed.
layer.of.atoms.[73]:.(a). T .=.400.K.and.(b). T .=.800.K..The.black.curves.show.the.atomic.densi-
ties,. and. the. red. curves. show. the. electronic. densities.. (Adapted. from. Walker,. B.G.. et. al.,.
J. Chem. Phys .,.124,.174702,.2006;.Walker,.B.G..et.al.,. J. Phys. Condens. Matter ,.18,.L269,.
2006..With.permission.)
Search WWH ::




Custom Search