YO:Eu and the Mössbauer isomer shift coefficient of Eu compounds fromsimulations.

We report on a full potential density functional theory characterization of YOupon Eu doping on the two inequivalent crystallographic sites 24and 8. We analyze local structural relaxation, electronic properties and the relative stability of the two sites. The simulations are used to extract the contact charge density at the Eu nucleus. Then we construct the experimental isomer shift (IS) versus contact charge density calibration curve, by considering an ample set of Eu compounds: EuF, EuO, EuF, EuS, EuSe, EuTe, EuPdand the Eu metal. The, expected, linear dependence has a slope of= 0.054 mm sÅ, which corresponds to nuclear expansion parameter Δ/= 6.0 × 10.allows to obtain an unbiased and accurate estimation of the IS for any Eu compound. We test this approach on two mixed-valence compounds EuSand EuSiN, and use it to predict the YO:Eu IS with the result +1.04 mm sat the 24site and +1.00 mm sat the 8site.