[gmx-users] OPLSAA + NAC-ACE

[Anton Feenstra]

Pawan Babel wrote:

> Hi all
> I am using OPLSAA forcefield with explicit water model on gromacs 3.2.1
> with NAC & ACE terminal as capping my peptide chain.
> 
> During pdb2gmx i am getting following error :
> Fatal error: Atom CH3 in residue NAC 15 not found in rtp entry with 6 atoms
>              while sorting atom
[...]

Entries in the .hdb should be atom *names*, it seems that by mistake
the atom *types* were entered. The CH3 probably should be CA, and you
should check the others as well.

> Default entry in ffoplsaa.hdb for ACE and NAC in gromacs 3.2.1 are :
> NAC     2
>         1       1       N       -C      CH3
>         3       4       CH3     N       -C
> 
> ACE     1
>         3       4       CH3     C       O
> =========================================
> and default entry in ffoplsaa.itp for ACE and NAC are:
> [ ACE ]
>  [ atoms ]
>     CA    opls_135   -0.180     1
>   HH31    opls_140    0.060     1
>   HH32    opls_140    0.060     1
>   HH33    opls_140    0.060     1
>      C    opls_235    0.500     2
>      O    opls_236   -0.500     2
[...]

-- 
Groetjes,

Anton
  _____________ _______________________________________________________
|             |                                                       |
|  _   _  ___,| K. Anton Feenstra                                     |
| / \ / \'| | | Dept. of Pharmacochem. - Vrije Universiteit Amsterdam |
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