**Implicit solvation methods**

MD simulations with explicit solvent molecules are computationally expensive and important properties such as solvation free energies may often converge slowly. Other computational approaches in which the influence of the solvent is incorporated implicitly are needed (see Roux and Simonson, 1999). Those include continuum electrostatics based on the Poisson-Boltzmann (PB) equations (Nina et al., 1997), stochastic Brownian Dynamics (Im et al., 2000), and mean-field theories based on statistical mechanical integral equations.