I am looking to the water adsorption from atmosphere by using Grand Canonical + MD (GCMD) within the GROMACS and Martini force field.
Till now I write a simple script which add a polarizable water molecule randomly and calculate the change in potential-energy. Then I used the accept/reject ratio for a micro state based on the exp (\mu -\Delta U) as explained in many references, e.g.
\mu = chemical potential which is considered as an ideal gas.
\Delta U = potential(N+1) - potential(N)
The problem is in my simulations /mu is always lower than \Delta U which means a very low chance for water adsorption. This is against hydrophilic nature of material.
Any idea or experience with GCMD in Martini?