I would like to use the ACE implicit solvation model to simulate a protein on a quartz surface. I have chosen ACE because I am using the MC module which supports only ACE or EEF1.

I need to find the atom volumes for the quartz atoms and add them to the solvation parameter file "solvpar22.inp". I thought that this might be easy because the surface is planar and the distance between the Oxygen atoms exposed to the solvent is between 4.4 and 4.9 A. Thus I think that I can use the van der Waals radius for O and Si to calculate the atom volumes and obtain a first rough approximation. Is this a reasonable approach or am I far off?

I was going to use the standard VDW radii:

http://www.ccdc.cam.ac.uk/support/documentation/conquest/ConQuest/conquest.3.353.html

Any hint is appreciated. Thanks!