Molecules change the shape in energy-minimization step

GROMACS version:4.5.5
GROMACS modification: No

Hi Gromacs users,

I want to keep the water shape in the energy-minimization step.
The HO bond length of Tip4p_ice water is 0.9572 A
but after the minimization, the bond length usually becomes ~0.97 A

I tried the Shake constraint in the energy-minimization step, but it shows that there are some errors, it can not work in the energy-minimization step.

I am not sure where the problem is. Does anyone have any suggestions?

Use SETTLE to constrain the water geometry. See any of the standard water topologies in GROMACS to make sure your topology has the right [settles] settings.