Re: [AMBER] About the Mg charge in AMBER FF

From: Jason Swails <>
Date: Fri, 4 Oct 2013 08:38:02 -0400

On Fri, Oct 4, 2013 at 8:07 AM, FyD <> wrote:

> Dear George,
> You might be interested in using R.E.D. Server at
> to derive atomic charges from
> molecular electrostatic potential(s), and let the charge fitting step
> decide what is the charge value for such a central Magnesium atom.

I think he was talking about magnesium ions free in solution. For free
ions, only a +2 charge makes sense. An alternative is to create a residue
with Mg complex to its surroundings, in which case some of Mg's polarizing
effects can be incorporated into the charge derivation of the entire
residue (this is where R.E.D. would be helpful).

Divalent metal ions are difficult (impossible?) to describe 'correctly' in
classical, fixed-charge force fields, and it is an area of active research.

All the best,

Jason M. Swails
Rutgers University
Postdoctoral Researcher
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Received on Fri Oct 04 2013 - 06:00:24 PDT
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