= Tetrahedral crystal field splitting
{title2=$\Delta_t$}
In the ideal tetrahedral point-charge model, the five metal <d orbitals> split into a lower twofold $e$ set and an upper threefold $t_2$ set. Relative to their weighted barycentre their energies are $-3\Delta_t/5$ and $+2\Delta_t/5$, where $\Delta_t>0$ is the separation. For occupancies $e^{n_e}t_2^{n_t}$, the <crystal field stabilization energy> is $(-0.6n_e+0.4n_t)\Delta_t$. Under weak-field high-spin filling it is $-0.6\Delta_t$, $-1.2\Delta_t$, $-0.8\Delta_t$ and zero for $d^6,d^7,d^8,d^{10}$ respectively. Shorter metal–ligand distances generally increase the splitting, so orbital filling can superimpose nonmonotonic bond-length changes on an ionic-size trend. The model alone does not determine an absolute <bond length>.
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