Local distortions with the substitution of Se for Te in FeSe$_{0.5}$Te$_{0.5}$

The isovalent substitution of Te for Se in the superconductor FeSe$_{1-x}$Te$_{x}$ increases T$_{c}$ in comparison to $\alpha$-FeSe but, on average, decreases the chalcogen-Fe bond angle. However, we find that the local symmetry is lower than the one presumed on average, \textit{P4/nmm}, because the Se and Te ions do not share the same site, and have two distinct textit{z}-coordinates exhibiting two types of bond angles and bond lengths with Fe. Simultaneously, ab-initio calculations based on spin density function theory yielded an optimized structure with distinct \textit{z} -coordinates for Se and Te, in agreement with the experiment.