Coherent tunneling in Cu2+- and Ag2+-doped MgO and CaO:Cu2+ explored through ab initio calculations -: art. no. 155107

The observation of coherent tunnelling in Cu2+- and Ag2+-doped MgO and CaO:Cu2+ was a crucial discovery in the realm of the Jahn-Teller (JT) effect. The main reasons favoring this dynamic behavior are now clarified through ab initio calculations on Cu2+- and Ag2+-doped cubic oxides. Small JT distortions and an unexpected low anharmonicity of the e(g) JT mode are behind energy barriers smaller than 25 cm(-1) derived through CASPT2 calculations for Cu2+- and Ag2+-doped MgO and CaO:Cu2+. The low anharmonicity is shown to come from a strong vibrational coupling of MO610- units (M=Cu,Ag) to the host lattice. The average distance between the d(9) impurity and ligands is found to vary significantly on passing from MgO to SrO following to a good extent the lattice parameter.