Electric double-layer structure in primitive model electrolytes: comparing molecular dynamics with local-density approximations.
We evaluate the accuracy of local-density approximations (LDAs) using explicit molecular dynamics simulations of binary electrolytes comprised of equisized ions in an implicit solvent. The Bikerman LDA, which considers ions to occupy a lattice, poorly captures excluded volume interactions between primitive model ions. Instead, LDAs based on the Carnahan-Starling (CS) hard-sphere equation of state capture simulated values of ideal and excess chemical potential profiles extremely well, as well as the relationship between surface charge density and electrostatic potential. Excellent agreement between the EDL capacitances predicted by CS-LDAs and computed in molecular simulations is found even in systems where ion correlations drive strong density and free charge oscillations within the EDL, despite the inability of LDAs to capture the oscillations in the detailed EDL profiles.
†Department of Chemical Engineering, University of California-Santa Barbara, Santa Barbara, California 93106, United States.|‡Lawrence Livermore National Laboratory, Livermore, California 94551, United States.
Brian
B
Giera
§Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
Neil
N
Henson
§Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
Edward M
EM
Kober
†Department of Chemical Engineering, University of California-Santa Barbara, Santa Barbara, California 93106, United States.
M Scott
MS
Shell
†Department of Chemical Engineering, University of California-Santa Barbara, Santa Barbara, California 93106, United States.
Todd M
TM
Squires