1 tip4p TIP4P TIP 4-point, recommended
2 tip3p TIP3P TIP 3-point
3 tip5p TIP5P TIP 5-point (see http://redmine.gromacs.org/issues/1348 for issues)
4 tip5pe TIP5P TIP 5-point improved for Ewald sums
5 spc SPC simple point charge
6 spce SPC/E extended simple point charge