tip3p   TIP3P   TIP 3-point, recommended
tip4p   TIP4P   TIP 4-point
tips3p  TIPS3P  CHARMM TIP 3-point with LJ on H's
tip5p   TIP5P   TIP 5-point (see http://redmine.gromacs.org/issues/1348 for issues)
spc     SPC     simple point charge
spce    SPC/E   extended simple point charge
