AMBER Archive (2009)

Subject: Re: [AMBER] help with parameters for ions

From: rebeca (
Date: Tue Jun 02 2009 - 12:38:00 CDT

Hi,thanks for the suggestion, I will change to tip4
the complete script is this one:

$AMBERHOME/exe/xleap -s -f $AMBERHOME/dat/leap/cmd/leaprc.ff99
loadamberparams frcmod.ionsjc_tip3p
loadoff system.lib
addions mol Na+ 30 Cl- 30
saveamberparm mol ionized.crd

In system.lib I have a library for my system, which is a carbon nanotube
using the CA carbons included in Amber.

The topology generated is exactly the same than that generated
with the same comands except for the loadamberparams frcmod.ionsjc_tip3p

What am I doing wrong?


Hi Rebeca,

You need to show the complete script of leap. I suspect that your atom
types are different from the names in the new frcmod file.

If your concern is the crystallization of KCl, you'd better use TIP4PEW or
SPC/E water and their ions. The solubilities of TIP3P-compatible ions are
also low. We are going to publish the data soon.

On Tue, 2 Jun 2009 09:46:40 -0400, "David A. Case"
<> wrote:
> On Tue, Jun 02, 2009, rebeca wrote:
>> I am doing simulations using a KCl concentration 1M and I have problems
>> of
>> crystallization of ions in the simulations. I have seen in the
>> that this is normal with Amber parameters for ions.
>> I have found a paper
>> "Determination of Alkali and Monovalent Ion Parameters for Use in
>> Explicitly Solvated Biomolecular Simulations"
>> S Joung, Thomas E Cheatham, J. Phys. Chem. B, Vol. 112, No. 30. (1 July
>> 2008), pp. 9020-9041.
> Frcmod files for these parameters are in the frcmod_ionsjc_* files in
> $AMBERHOME/dat/leap/parm. You can use those directly, and also see how
> frcmod files were created, in case you want to use your own or other
> parameters.
> ...hope this helps...dac
> _______________________________________________
> AMBER mailing list

Rebeca García Fandiño
Molecular Modelling and Bioinformatics Group
Institut de Reçerca Biomèdica 
Parc Cientific de Barcelona
08028 Barcelona

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