[gmx-users] K+ atom type and KCl crystals

[Marc Baaden]

Hi,

We had the same issue about K+ parameters. Currently we do use
the OPLSAA K+ with the Gromos forcefield. Find attached the included
file. But be aware that mixing forcefields is an insecure domain
(although ions are always an issue).

BTW, concerning K+ and in particular KCl, we have witnessed a number
of crystallization events of KCl crystals at physiological concentration
with Amber, but not with Gromacs so far.

Have other people also seen this ? I guess it's a K+ parameter problem.
Any tips or tricks ?

Cheers,
  Marc Baaden


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[ atomtypes ]
; full atom descriptions are available in ffoplsaa.atp
; name  bond_type    mass    charge   ptype          sigma      epsilon
 opls_408   K+     39.09830     1.000       A    4.93463e-01  1.37235e-03

[ moleculetype ]
; molname       nrexcl
K+              1

[ atoms ]
; id    at type         res nr  residu name     at name  cg nr  charge   mass
1       opls_408        1       K+              K        1      1        39.0983

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 Dr. Marc Baaden  - Institut de Biologie Physico-Chimique, Paris
 mailto:baaden at smplinux.de      -      http://www.marc-baaden.de
 FAX: +33 15841 5026  -  Tel: +33 15841 5176  ou  +33 609 843217