[gmx-users] reaction field kappa and ionic strength

[David van der Spoel]

Daniela S. Mueller wrote:
> dear all,
> 
> there are errors in the code regarding 1) the equation for kappa, which 
> is used for the reaction field method; and 2) in the calculation of the 
> ionic strength.
> 
> 1) in rf_util.c kappa is calculated as
> *kappa  = sqrt(2*I/(EPSILON0*eps_rf*BOLTZ*Temp));
> 
> but the factor 2 in the square root is only correct if the sum in the 
> ionic strength I is actually divided by 2, which it isn't. so the factor 
> 2 should be omitted.
> 
> 2) in force.c the ionic strength is (among others) calculated by summing 
> the absolute values instead of the squares of the charges.
> zsq += fabs(q);
> this is only correct for monovalent charge groups.
> 
> @developers: these errors have been remarked previously on the mailing 
> list. as it is not mentioned in the bugzilla, i thought i can bring it 
> up again... can you correct this in the code for the next version please?
> 
> thanks.
> 
> best regards,
> daniela
> 
I vaguely recall something like that, probably before bugzilla even. But 
  could you please submit a bugzilla? Otherwise we might well forget it 
again...

-- 
David.
________________________________________________________________________
David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se
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