Theoretical prediction of local distortion in an ErO6 cluster: Stabilization of a C4v structure by a rack and pinion effect

As a possible atomic coordination of erbium dopants surrounded by oxygen, a molecular orbital calculation of an ErO6 cluster can predict a C4v pseudo-octahedral structure with Er distortion of ∼0.1 Å from the octahedral center. It was found that bond alternation by a “rack and pinion effect” can minimize the electron transfer from O2− to Er3+ at this distortion range, resulting in stable ionic bonding; the rotation of an O 2p orbital due to Er 5d translation, similar to rack and pinion motion, forms a new O 2p–Er 5d bond, while a dipole moment induced by symmetrical degradation makes an O 2p–Er 6s bond unstable.