

Tahmid,

Are you constraining the geometry of the water molecule (bond and angle)
with SHAKE?  With SPC, your hydrogens have no lennard-jones terms and
but they do have charge.  If you don't constrain these hydrogens they
can easily cause your calc. to blow up.

Mark

Mark A. Thompson                    
Sr. Research Scientist              email:  [email-masked]
Molecular Science Research Center   FAX  :  509-375-6631
Pacific Northwest Laboratory        voice:  509-375-6734
PO Box 999, Mail Stop K1-90
Richland, WA.  99352
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