Potential of Mean Force for Ca2+ at the Cleaved Mica−Water Interface

Monte Carlo simulations reveal that in the water coverage range of 0−28 H 2 O/Ca 2+, Ca 2+ is specifically adsorbed above tetrahedral substitutions of Si by Al at distances of 1.53−1.72 Å from the cleaved mica surface. A random distribution of Ca 2+ on mica is found to be strongly unfavorable as compared to the regular one. At the highest simulated water coverage, inner-sphere adsorption of Ca 2+ at 1.72 Å is more favorable by 121 kJ/mol than its outer-sphere adsorption at 3.99 Å. The activation energy for Ca 2+ desorption from the mica surface is calculated to be 144 kJ/mol, which is lower by ∼20 kJ/mol and higher by ∼60 kJ/mol than recently reported values for Mg 2+ and K + desorption, respectively.