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--- documentation:standard_operators:charge_quadrupole:start [2016/10/06 08:21] – created Maurits W. Haverkort
+++ documentation:standard_operators:charge_quadrupole:start [2025/11/20 03:29] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
+{{indexmenu_n>9}}
+====== Charge quadrupole operators (Q) ======
+###
+The quadrupole operator is a special case of the crystal-field operator. The operator is defined as:
+\begin{equation}
+Q_{ij} = 3r_ir_j/r^2 - \hat{r}\cdot\hat{r}\delta_{i,j}.
+\end{equation}
+Whereby we need to note that we here only take the angular part of a quadrupole. It's "strength", i.e. the expectation value of $r^2$ is omitted from our definition.
+###
+===== Table of contents =====
+{{indexmenu>.#1|msort nsort}}