  Molecular dynamics (MD) simulations of ions (K$^+$, Na$^+$, Ca$^{2+}$ and
Cl$^-$) in aqueous solutions are investigated. Water is described using the
SPC/E model. A stochastic coarse-grained description for ion behaviour is
presented and parameterized using MD simulations. It is given as a system of
coupled stochastic and ordinary differential equations, describing the ion
position, velocity and acceleration. The stochastic coarse-grained model
provides an intermediate description between all-atom MD simulations and
Brownian dynamics (BD) models. It is used to develop a multiscale method which
uses all-atom MD simulations in parts of the computational domain and (less
detailed) BD simulations in the remainder of the domain.
