reaction field kappa and ionic strength
errors in the code regarding
1) *kappa in rf_util.c, which is used for the reaction field method; and
2) calculation of ionic strength.
1) in rf_util.c line 180, *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 in *kappa^2 should be omitted, or the ionic strength should be
divided by 2.
2) in force.c line 880, the ionic strength is calculated by summing the absolute
values of the charges, but should be the squares of the charges.
zsq += fabs(q);
this is only correct for monovalent charge groups.
#1 Updated by Berk Hess over 13 years ago
I have fixed these bugs nearly a year ago,
but since then we have not (yet) released an update to 3.3.1.
Note that these errors only occur with generalized reaction field,
not plain reaction field.
We were considering removing GRF, since if electrostatics
are important, one should anyhow use PME.
Thanks for reporting these bugs,