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I need to calculate the dipole correlation function for the changes in the dipole along
What do you need that for?
the OH bond and for it I need the instantaneous dipole along the OH bond. Can it
be done, as the SHAKE algorithm keeps the constraints and thereby makes SPC water rigid.
If you cannot answer this question by yourself by now, you should not be doing computer simulations. A simulation software will never do the thinking for you and it looks to me that this is where have not spent enough time on.
Will working with morse type potential be useful? Is there any provision to use flexible SPC
Doing guessing is a bad way to do research, especially in a field where a lot of research has already been done an a large amount of published literature already exists. I suggest some time on that an try to find out, whether a classical MD simulation can even give a useful answer to your questions. A lot of things are possible to simulate with lammps, but not all of them will result in meaningful data.