[gmx-users] Charges in SW water model

[Andreas Kring]

Dear Professor Spoel.

I have a question concerning your article on the SW water model 
published in J. Phys. Chem. B, 105, 2618-2626 (2001). I guess the 
question is only indirectly related to GROMACS, but I'll post in on the 
mailing list since it may be of interest to other GROMACS users as well.

Equation (4) of the paper states that

k_nn = (q_s)^2/alpha_nn,

where nn is either xx, yy or zz. k is the spring constant, q_s is the 
charge and alpha is the polarizability. The first line in section 2.2 of 
the paper is "After determining the charges and spring constants 
corresponding to the polarizabilities...". It seems as if the are too 
many unknowns in the equation above, or do I miss something?

If I understand it correctly, the spring constants are determined from 
q_s and alpha. But how is the charge determined?

Hope you can help with this question.

Kind regards
Andreas

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Andreas Kring, Ph.D.-student
University of Copenhagen
Niels Bohr Institute
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DK-2100 Copenhagen
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