The following figure is the electron localization function (ELF) for monolayer LaBr$_2$.
The ELF is calculated to reflect the bonding character in SL LaBr$_2$. As shown in the figure, ELF shows two localization areas: one is located around La (brown color) and the other around Br (grey color) atoms. Almost no electron is localized between La and Br atoms, suggesting the typical ionic bonding, with La atoms donating electrons to Br atoms.
However, this bond character can be understood from the charge density plot. So what's the difference between charge density and the electron localization function (ELF)? What else can we read from the ELF plot?