Ligand relaxation in copper- and silver-atom-doped alkali halides

Through an analysis of the experimental isotropic superhyperfine constant $A_s$ of ${\mathrm{Cu}}^0$ and ${\mathrm{Ag}}^0$ in several alkali halides, it is clearly demonstrated that significant outward ligand relaxations are involved in these cases. This analysis requiring accurate values of the overlap integral $S_s$ allows one to estimate the true value of the impurity-ligand distance $R$. Such estimations point out that, for a given alkali chloride lattice, the ${\mathrm{Ag}}^0$-${\mathrm{Cl}}^{-}$ distance is about 0.10 Å larger than the ${\mathrm{Cu}}^0$-${\mathrm{Cl}}^{-}$ distance which is consistent with the higher size of ${\mathrm{Ag}}^0$. The present work proves reasonably that, though $\frac{(R-R_0)}{R_0}$ ($R_0$ corresponding to the host lattice) can be up to 27%, the values of $R$ follow those of $R_0$ through the series of alkali chlorides for both ${\mathrm{Cu}}^0$ and ${\mathrm{Ag}}^0$. This is also consistent with the reported analysis of the ${\left(\mathrm{A}\mathrm{g}{\mathrm{Cl}}_5\mathrm{B}\mathrm{r}\right)}^{6-}$ complex in KCl. Finally, the present work supports the idea that the ratio of the covalent contribution $\gamma p\sigma$ to the ligand $p\sigma$ admixture and the corresponding overlap contribution $S_{p\sigma }$ decreases when $R$ decreases in the ${\left(\mathrm{A}\mathrm{g}{\mathrm{Cl}}_6\right)}^{6-}$ complex.