[gmx-users] Fwd: Implementing GoIP parameters in OPLSAA

[ingram]

Dear GROMACS gremlins,

I am trying in vain to implement the GoIP parameters for a gold-peptide 
interface in the OPLSAA ff. I began with just one kind of Au atom and 
now I want to put in two.

When I execute gmx grompp -f em.mdp -c Au111.gro -p topol.top -o em.tpr

I get this error
Fatal error:
Something is wrong in the coordinate formatting of file Au111.gro. Note 
that gro is fixed format (see the manual)
For more information and tips for troubleshooting, please check the 
GROMACS

Here is my .gro file

New structure; 1Created by VESTA
     4
     1AU        AUI    1   0.000   0.000   0.240
     1AU        AUS    2   0.022   1.282   0.240
     1AU        AUI    3   0.045   2.564   0.240
     1AU        AUS    4   1.929   0.000   0.240
     0.00000   0.00000   0.00000

And my .top file:

; Include forcefield parameters
#include "./oplsaa_Au.ff/forcefield.itp"

[ moleculetype ]
; Name            nrexcl
Other               3

[ atoms ]
;   nr       type  resnr residue  atom   cgnr     charge       mass  
typeB    chargeB      massB
; residue   1 AU  rtp AU   q  0.0
     1      opls_966      1      AU    AUI   1       0.0       79      ; 
qtot 0
     2      opls_967      1      AU    AUS   2      -0.3       79      ; 
qtot 0
     3      opls_966      1      AU    AUI   3       0.0       79      ; 
qtot 0
     4      opls_967      1      AU    AUS   4      -0.3       79      ; 
qtot 0

;Include Position restraint file
#ifdef POSRES
#include "posre.itp"
#endif

[ system ]
;Name
New structure; 1Created by VESTA

[ molecules ]
;Compound        #mols
Other               1

And the ffnonbonded.itp:
  opls_966   AUI   79   196.96657     0.0         A    3.20000e-01  
6.50000e-01
  opls_967   AUS   79   196.96657    -0.3         A    0.00000e-01  
0.00000e-01
  opls_968   AUB1  79   196.96657     0.0         A    0.00000e-01  
0.00000e-01
  opls_969   AUB2  79   196.96657     0.3         A    0.00000e-01  
0.00000e-01

(there are extra Au atoms as I will eventually be adding more kinds)

I also changed the residuetype.dat file to include:
AUI     Ion
AUS     Ion


I can't see where I've gone wrong  as I read that grompp does not read 
the .rtp file or .atp. Also can you explain to me what is the difference 
between atom_type (eg opls_XXXX) and atom (eg AUI).

Thanks for your help