how to calculate crystal field stabilisation energy?

It is a simple matter to calculate this stabilisation since all that is needed is the electron configuration.

For an octahedral complex, an electron in the more stable t_2gsubset is treated as contributing-2/5?whereas an electron in the higher energy e_gsubset contributes to a destabilisation of+3/5?.

The final answer is then expressed as a multiple of the crystal field splitting parameter ? (Delta).

Based on this, the Crystal Field Stabilisation Energies for d⁰to d¹⁰configurations can then be used to calculate the Octahedral Site Preference Energies, which is defined as:OSPE = CFSE (oct) - CFSE (tet)