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Neutral atoms in ionic lattices: Stability and ground state properties of KCl:Ag(0)

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The equilibrium geometry of Ag0 centers formed at cation sites in KCl has been investigated by means of
total-energy calculations carried out on clusters of different sizes. Two distinct methods have been employed:
First, an ab initio wave-function based method on embedded clusters and second, density-functional theory
~DFT! methods on clusters in vacuo involving up to 117 atoms. In the ab initio calculations the obtained
equilibrium Ag0
-Cl2 distance Re is 3.70 Å, implying a large outward relaxation of 18%, along with 7%
relaxation for the distance between Ag0 and the first K1 ions in ^100& directions. A very similar result is
reached through DFT with a 39-atom cluster. Both approaches lead to a rather shallow minimum of the
total-energy surface, the associated force constant of the A1g mode is several times smaller than that found for
other impurities in halides. These conclusions are shown to be compatible with available experimental results.
The shallow minimum is not clearly seen in DFT calculations with larger clusters. The unpaired electron
density on silver and Cl ligands has been calculated as function of the metal-ligand distance and has been
compared with values derived from electron-paramagnetic resonance data. The DFT calculations for all cluster
sizes indicate that the experimental hyperfine and superhyperfine constants are compatible when Re is close to
3.70 Å. The important relation between the electronic stability of a neutral atom inside an ionic lattice and the
local relaxation is established through a simple electrostatic model. As most remarkable features it is shown
that ~i! the cationic Ag0 center is not likely to be formed inside AgCl, ~ii! in the Ag0 center encountered in
SrCl2, the silver atom is probably located at an anion site, and ~iii! the properties of a center-like KCl:Ag0
would experience significant changes under hydrostatic pressures of the order of 6 GPa.

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Reproducció digital del document publicat en format paper, proporcionada per PROLA i http://dx.doi.org/10.1103/PhysRevB.62.13356

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Articles publicats en revistes (Ciència dels Materials i Química Física)

# metadata.dc.title[].value
Neutral atoms in ionic lattices: Stability and ground state properties of KCl:Ag(0)