[gmx-users] SPC Water Bond Lengths

[David Ackerman]

Hello,

I had a question regarding SPC water. I know that SPC water is rigid with
constrained bond lengths. However, I have noticed in my simulations that
the OH bond lengths and H-H distances can vary somewhat significantly. For
instance, I have run simulations containing ~140000 SPC waters, and the
average OH bond length is around ~0.79 Angstroms, with a max of 1 and a
minimum of nearly 0. Also, dppc128.pdb from
http://people.ucalgary.ca/~tieleman/download.html, which utilized SPC
waters, also has an average OH bond length of ~0.79 Angstroms. In both
cases, I see a distribution in bond lengths that is very high near 1
Angstrom, and dies off as it approaches 0.

I was wondering if this is expected. Assuming the water is rigid, should
the bond lengths remain more fixed than what I am seeing?

I apologize if this is an ignorant question, but aside from seeing that SPC
water is supposed to be rigid, I have seen no mention of bond length
distributions.

Thank you for your time,
David