I also found this usefull, but have a question on what one would consider the
standard. from eyeballing mostly the charges I get for .itp files from PRODRG
server fall into mullikin charges, but usually 3-4 dont or have no charge, but
I woundered if the ESP or AIM charges would be beter. From the web page
http://cccbdb.nist.gov/ which gives an overload of charge, angle etc tables and
how they were determined.
ESP Electrostatic potential. The electrical potential due to the nuclei and
electrons in the molecule, as experienced by a test charge.
AIM Atoms-in-molecules. An analysis method based upon the shape of the
total electron density; used to define bonds, atoms, etc. (5). Atomic charges
computed using this theory are often quite different from those from other
analyses (e.g., from Mulliken populations). Such charges are probably the most
justifiable theoretically, but meet some resistance because the values obtained
may be quite different from those from older theories (6).
In addition, how would AIM charges play out in Gromacs, especially with center
points in rings which are different from nuclear centers, but representative of
PI orbitals, etc...With some say dummy point lacking geometry (not that I would
ever do that, but I do often wounder about representation of PI interactions in
simulations, such as say a metal ion trapped between two benzene rings by PI)
And as an example, this is a partial table of a molecule--
Computed charges for C6H5NH2 (aniline)
HF/3-21G
Charge (e)
Number Element Mulliken chelpg AIM ESP
1 C 0.390 0.715
2 C -0.269 -0.486
3 C -0.211 -0.037
4 C -0.278 -0.316
5 C -0.211 -0.037
6 C -0.269 -0.486
7 N -0.984 -1.143
8 H 0.224 0.203
9 H 0.236 0.152
10 H 0.229 0.171
11 H 0.236 0.152
12 H 0.224 0.203
13 H 0.341 0.453
14 H 0.341 0.453
Basically, I woundered which would be more proper charge wise in constructing
small, or medium sized molecules.
Stephan Watkins
--Sorry its an answere with a question attached.
Today's Topics:
1. RE: Umbrella sampling of phosphate ion binding (Dallas Warren)
----------------------------------------------------------------------
Message: 1
Date: Thu, 09 Jun 2011 01:30:34 +0000
From: Dallas Warren <[email protected]>
Subject: RE: [gmx-users] Umbrella sampling of phosphate ion binding
To: Discussion list for GROMACS users <[email protected]>
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="us-ascii"
You have been provided there with the reference in which the parameters for the
molecule were derived.
Read it!
And determine yourself if it is applicable or not to what you are doing and the
forcefield you are using.
Catch ya,
Dr. Dallas Warren
Medicinal Chemistry and Drug Action
Monash Institute of Pharmaceutical Sciences, Monash University
381 Royal Parade, Parkville VIC 3010
[email protected]
+61 3 9903 9304
---------------------------------
When the only tool you own is a hammer, every problem begins to resemble a nail.
From: [email protected] [mailto:[email protected]] On
Behalf Of bharat gupta
Sent: Thursday, 9 June 2011 11:29 AM
To: [email protected]; Discussion list for GROMACS users
Subject: Re: [gmx-users] Umbrella sampling of phosphate ion binding
I found it in the /shared/top/ gmx.ff folder . Here's the file
;
; Force field based on GROMOS with new charges as described in
; D. van der Spoel, K.A. Feenstra, M.A. Hemminga and H.J.C. Berendsen:
; Molecular modeling of the RNA binding N-terminal part of cowpea chlorotic
; mottle virus coat protein in solution with phosphate ions
; Biophys. J. 71 pp. 2920-2932 (1996)
;
[ moleculetype ]
; name nrexcl
h2po4 4
[ atoms ]
; nr type resnr residu atom cgnr charge mass
; use charges from Janez Mavri
1 OA 1 PI O1 1 -0.777
2 OA 1 PI O2 1 -0.777
3 OM 1 PI O3 1 -0.943
4 OM 1 PI O4 1 -0.943
5 P 1 PI P 1 1.596
6 HO 1 PI H1 1 0.422
7 HO 1 PI H2 1 0.422
[ bonds ]
; ai aj funct c0 c1
5 1 1 1.637000e-01
5 2 1 1.637000e-01
5 3 1 1.478000e-01
5 4 1 1.478000e-01
6 1 1 0.943000e-01
7 2 1 0.943000e-01
[ angles ]
; ai aj ak funct c0 c1
2 5 1 1 1.015000e+02 400
3 5 1 1 1.059000e+02
4 5 1 1 1.082000e+02
3 5 2 1 1.059000e+02
4 5 2 1 1.082000e+02
4 5 3 1 1.248000e+02
6 1 5 1 1.082000e+02
7 2 5 1 1.082000e+02
[ dihedrals ]
; ai aj ak al funct
6 1 5 2 1
7 2 5 1 1
Can I use it or not ??
On Thu, Jun 9, 2011 at 10:26 AM, Justin A. Lemkul
<[email protected]<mailto:[email protected]>> wrote:
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