[Chimera-users] coloumbic coloring when surface can't be calculated?

Hi, I have a structure (well, lots of structures) for which surface calculation fails in Chimera. I can rescue surface calculation using the ‘grid’ option (e.g. surf #0 grid 1), but then I can’t figure out how to apply coulombic coloring to that surface. I could use APBS, but PDB2PQR seems to choke on especially large/complicated structures. Is there any way around this? Would it be possible to export the coloumbic potential as a .dx file and use that for electrostatic surface coloring? Cheers Oli