Unification of the point charge electrostatic model with the chemical shift model for lanthanide 5d states

The relationship between the chemical shift of the 5d-electron binding energy and the 5d-electron 10Dq crystal field splitting for Ce3+ and Eu2+ in octahedral, cubic and cuboctahedral configuration has been investigated. The traditional point charge electrostatic model (PCEM) largely underestimates the size of the 10Dq crystal field splitting, and it also does not correctly reproduce how 10Dq changes with lanthanide charge. In the recently proposed chemical shift model to determine the absolute 4f and 5d electron binding energies a screening charge of equal but opposite size than the lanthanide charge, that is located at a screening distance slightly larger than the radius of the lanthanide, was introduced to derive electron binding energies. Here we will demonstrate that when similar concepts are introduced for the PCEM, much better 10Dq values are obtained. We will further establish that trends in chemical shift with varying chemical environment, that are strongly related to the nephelauxetic effect, also appear in the value for 10Dq.