AMBER Archive (2002)

Subject: divalent cations parameters

From: Apostoluk, Wlodzimierz K (Wlodek_at_pnl.gov)
Date: Mon Sep 30 2002 - 17:38:11 CDT

Hello,

Bill Ross and David Case pointed me to Amber FAQ web site regarding
conversion of parameters form Aqvist's paper to parm99 force field. Indeed,
there is an example regarding conversion of Ca2+ parameters. However values
reported there still do not match parm99 force field. First, calculated
value of R* is 1.3264 A, whereas in the parm99 file for Ca2+ there is 1.7131
A. Second, the epsilon value is also different, but in this case probably
due to assumption that epsilon values for SPC and TIP3P water models are the
same, at least the difference is not so big (when it is taken into
consideration the values are exactly the same).
This concerns also Mg2+ ion parameters, however difference between R* values
is lower then in case of Ca2+.
I was wondering if somebody could explain where the R* differences come
from?

Thanks in advance for the help,

Wlodek Apostoluk