NUMERICAL CONSIDERATIONS IN THE COMPUTATION OF THE ELECTROSTATIC FREE-ENERGY OF INTERACTION WITHIN THE POISSON-BOLTZMANN THEORY

We evaluate two different ways of calculating the contribution of the electrostatic stress to the free energy integral based on Sharp and Ho nig's method within the finite difference nonlinear Poisson-Boltzmann equation method with the University of Houston Brownian Dynamics progr am. We show that only one of these approaches gives consistent results in the limit of zero ionic concentration for interactions of the orde r of magnitude of the hydrogen bond. The results are compared with res ults from both the linear Poisson-Boltzmann equation and the Debye-Huc kel theory, for ion concentrations within the limits of validity of th ese approximate methods. We demonstrate this by application to DNA mol ecules. (C) 1997 Academic Press.