The excited states, 4T2g and 2Eg, of a Cr impurity in Al2O3 were treated by constraint density functional theory by imposing a density matrix constraint (constraint field) to control the electron occupation numbers of the d orbitals. The calculated excitation energies, directly calculated from the self-consistent total energies of the 4A2g ground states and the various excited states, correctly reproduce the experimental ordering. In addition, we find that there is no stationary solution for the excited 4T2g state corresponding to the crystal-field transition state in the usual Kohn-Sham equation, i.e., with no constraint field. By contrast, the excited 2Eg state of the spin-flip transition state is a (meta-) stable stationary solution, and may be responsible for the long radiative decay lifetime observed in experiments on ruby.
|Original language||English (US)|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - May 10 2013|
ASJC Scopus subject areas
- Condensed Matter Physics
- Electronic, Optical and Magnetic Materials