Grand-canonical Monte-Carlo simulation of DNA condensation in equilibrium with a salt mixture containing 2:2 salt

The Grand canonical Monte Carlo simulation method is used to simulate DNA hexagonal condensate in the presence of a mixture of 1: 1, 2: 1, 2: 2 salts using the primitive ion model. Previous results show that DNA can be condensed by divalent counterions in restricted environment, such as inside viruses. In this work, we study the effects of divalent co-ions on condensation of DNA by divalent counterions. It is shown that divalent co-ions lead to weaker DNA condensation free energy and DNA de condensation at smaller counterions concentration.