To what extent of ion neutralization can multivalent ion distributions around RNA-like macroions be described by Poisson

To what extent of ion neutralization can multivalent ion distributions around RNA-like macroions be described by Poisson–Boltzmann theory?

Xiong Gui, Xi Kun, Zhang Xi^†, Tan Zhi-Jie^‡

(color online) Maximum deviation of as a function of reduced surface charge density σ_r ( due to ion binding to the RNA-like spherical macroions in (a)–(c) divalent and (d)–(f) trivalent salt solutions. The radii of the RNA-like spherical macroions are 10 Å, 20 Å, and 30 Å, respectively. The dashed lines denote the of 4%.