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]