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

From: Andreas Goetz <agoetz.sdsc.edu>
Date: Fri, 4 Oct 2013 19:20:35 -0700

There is some reasoning for charge scaling with successful applications. See for example

Leontyev, Stuchebrukhov, PCCP 13 (2011) 2613.
Vazdar, Jungwirth, Mason, JPCB 117 (2013) 1844.

Jungwirth applies (apparently with success) what Leontyev and Stuchebrukhov suggested: scaling ion charges by 0.75 to account for dielectric screening in bulk (water).

All the best,
Andy

--
Dr. Andreas W. Goetz
Assistant Project Scientist
San Diego Supercomputer Center
Tel  : +1-858-822-4771
Email: agoetz.sdsc.edu
Web  : www.awgoetz.de
On Oct 4, 2013, at 5:38 AM, Jason Swails wrote:
> On Fri, Oct 4, 2013 at 8:07 AM, FyD <fyd.q4md-forcefieldtools.org> wrote:
> 
>> Dear George,
>> 
>> You might be interested in using R.E.D. Server at
>> http://q4md-forcefieldtools.org/REDS/ 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
> 
> -- 
> Jason M. Swails
> BioMaPS,
> Rutgers University
> Postdoctoral Researcher
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Received on Fri Oct 04 2013 - 19:30:03 PDT