## atomic charge

https://doi.org/10.1351/goldbook.AT06994
The charge attributed to an atom $$A$$ within a molecule defined as $$\zeta =Z_{\text{A}}- q_{\text{A}}$$, where $$Z_{\text{A}}$$ is the @A00499@ of $$A$$ and $$q_{\text{A}}$$ is the @E01986@ assigned to $$A$$. The method of calculation of $$q_{\text{A}}$$ depends on the choice of the scheme of partitioning @E01986@. In the framework of the Mulliken population analysis $$q_{\text{A}}$$ is associated with the so-called gross atomic population: $$q_{\text{A}}=\sum q_{\mu}$$, where $$q_{\mu }$$ is a gross population for an orbital $$\mu$$ in the @BT06999@ employed defined according $q_{\mu } = P_{\mu \mu }+\sum _{\begin{array}{c} \nu \neq \mu \end{array}}P_{\mu \nu }\ S_{\mu \nu }$ to where $$P_{\mu \nu }$$ and $$S_{\mu \nu }$$ are the elements of density matrix and overlap matrix, respectively (see @O04357@). In the Hückel @M03996@ theory (where $$S_{\mu \nu } = \delta _{\mu \nu }$$), $$q_{\mu } = n_{\mu }\ P_{\mu \mu }$$, where $$n_{\mu}$$ is the number of electrons in the MO$$\mu$$.
Source:
PAC, 1999, 71, 1919. (Glossary of terms used in theoretical organic chemistry) on page 1924 [Terms] [Paper]