Charge localization in multiply charged clusters and their electrical properties: some insights into electrospray droplets

The surface composition of charged Lennard-Jones clusters A(N) (n+), composed of N particles (55 ≤ N ≤ 1169) among which n are positively charged with charge q, thus having a net total charge Q = nq, is investigated by Monte Carlo with Parallel Tempering simulations. At finite temperature, the surface sites of these charged clusters are found to be preferentially occupied by charged particles carrying large charges, due to Coulombic repulsions, but the full occupancy of surface sites is rarely achieved for clusters below the stability limit defined in this work. Large clusters (N = 1169) follow the same trends, with a smaller propensity for positive particles to occupy the cluster surface at non-zero temperature. We show that these charged clusters rather behave as electrical spherical conductors for the smaller sizes (N ≤ 147) but as spheres uniformly charged in their volume for the larger sizes (N = 1169).