Hückel orbital charge density
= Hückel orbital charge density
{c}
{title2=$n_i=\sum_k f_k|c_{ik}|^2$}
In an orthonormal <Hückel method> basis, an occupied <molecular orbital> with occupancy $f_k$ contributes $f_k|c_{ik}|^2$ electrons to site $i$. Adding one electron to a fixed orbital changes the site population by $|c_i|^2$. A coefficient sign indicates orbital phase, not charge sign. A net atomic charge also needs a reference population and treatment of the electrons outside the model.