Figure : Ion diffusion as a function of moisture index in secondary cell wall of woody plants. We calculate the diffusion of cations (Na + , K + and Cu 2+ ) and anion (Cl -). Overall, ion diffusion increases as the moisture index increases. For KCl and CuCl2 at 0.1 M initial concentration, diffusion coefficients were previously measured using time-lapse X-ray fluorescence microscopy (XFM) . Scatter circles and triangles with no face color represent the experimental data for the respective cation (K + and Cu 2+ ) and anion (Cl -). Atomic level molecular diffusion agrees within an order of magnitude with microscale scale diffusion measurements. Similar to observations reported in XFM experiments, we find in MD simulations that K + diffuses faster than Cu 2+ ions.