Structure of Liquid Metal Surfaces: A First Principles Perspective - Metallic Systems: A Quantum Chemist's Perspective - page 159

more.surprising.is.that.strong.Friedel.oscillations.were.seen.to.be.present.for. liquid .
surfaces..Though.the.atomic.arrangements.used.in.the.formation.of.liquid.surfaces.
differed. greatly,. the. response. in. the. valence. electron. density—displaying. Friedel.
oscillations—was.remarkably.uniform.
Atomistic.simulations.have.also.indicated.that.there.should.be.ordering. within .the.
planes.of.the.layers.formed.at.the.surfaces.of.liquid.metals..Early.simulations.indicated.
that.there.should.be.hexatic.ordering.within.the.plane.of.the.surface.for.supercooled.
Au.surfaces..The.ensemble.DFT/MD.simulations.on.sodium.that.have.been.discussed.
in.this.chapter.favor.a.predominantly.ivefold-coordinated.ordering,.interspersed.with.
signiicant.numbers.of.atoms.having.fewer.neighbors.(fourfold-coordinated).as.well.
as.more.neighbors.(sixfold-coordinated.ordering)..The.proportion.of.atoms.with.ive-.
and.sixfold.coordination.increases.as.the.temperature.decreases.(an.observation.that.
correlates.with.the.expected.reduction.in.disorder.at.lower.temperature)..The.pres-
ence.of.ivefold.ordering.may.connect.with.the.observation.of.ivefold.local.symme-
try.(due.to.icosahedral.fragments.of.liquid.atoms).at.the.interface.between.a.liquid.
metal.and.a.solid.substrate.[81]..From.the.experimental.point.of.view,.the.existence.
and.nature.of.any.order.within.the.surface.layers.is.as.yet.unresolved.
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