vinothkumar mohanakrishnan wrote:
Dear Justin

what corrections i should make to ffoplsaan.itp to make it correct. what i should give instead of CAB and CLAA?.


You must use atom types, not names. Unfortunately, you've chosen to use atom names, which are also types, which makes all of this quite confusing if you're not sure what you're doing.

You defined two new atom types - opls_966 (CAB) and opls_967 (CLAA), which are the only indicators you are allowed to use if introducing new types. Thus, references to atom names (CAC, CLAD) will generate fatal errors.

i copied the .rtp .atp .itp files from usr/local/gromacs/share/gromacs/top to my working directory and added these parameters to the corresponding files. what you mean is should i need to add these parameters to the source directory ( usr/local/gromacs/share/gromacs/top)?


Your topology needs to be consistent with whatever files need to be included. By default, Gromacs checks the working directory first, but if you've moved to a new (sub)directory to carry out further steps, the grompp will not find your modified files, but will instead locate only the default force field files in $GMXLIB. Either keep all your work in one directory (which can get messy), or make use of the "include" keyword in the .mdp file. Any directory specified there will be searched after the working directory, but before $GMXLIB.

-Justin

Regards
Vinoth

On Mon, Oct 18, 2010 at 5:27 PM, Justin A. Lemkul <jalem...@vt.edu <mailto:jalem...@vt.edu>> wrote:



    vinothkumar mohanakrishnan wrote:

        Hi all

        i added new atomtype for dichloroethane (DCE) and added the
        corresponding parameters in the .rtp, .atp, .bon.itp, .nb.itp
        respectively. given below are my additions to the corresponding
        files respectively.

        *ffoplsaa.rtp*

        [ DCE ]
         [ atoms ]
         CLAA opls_967 -0.2270  1
         CAB  opls_966  0.2270  1
         CAC  opls_966  0.2270  2
         CLAD opls_967 -0.2270  2

        [ bonds ]
         CLAA    CAB
         CAB    CAC
         CAC    CLAD

        [ angles ]
         CLAA    CAB    CAC
         CAB    CAC    CLAD

        [ dihedrals ]
         CLAA    CAB    CAC    CLAD

        *ffoplsaa.atp*

         opls_966   14.02700  ; CH2 for DCE
         opls_967   35.45300  ; CL for DCE

        *ffoplsaabon.itp*

        [bondtypes]
        CLAA  CAB     1    0.17870   194137.6   ; CL-CH2 for DCE
        CAB   CAC     1    0.15300   259408.0   ; CH2-CH2 for DCE
        CAC   CLAD    1    0.17870   194137.6   ; CL-CH2 for DCE

        [angletypes]
        CLAA  CAB   CAC       1   108.200    368.192   ; C-C-CL for DCE
        CAB   CAC   CLAD      1   108.200    368.192   ; C-C-CL for DCE

        [dihedraltypes]
CLAA CAB CAC CLAD 3 20.76096 -0.4184 27.011904 0.00000 0.00000 0.00000 ; for DCE


    You shouldn't be using atom names in the [*types] directives.  What
    you should be using are the interpolated types from ffoplsaanb.itp,
    thus you have only utilized opls_966 (CAB) and opls_967 (CLAA).

        *ffoplsaanb.itp*


        opls_966   CAB    6    14.02700    0.227       A    3.98000e-01
         4.76976e-01 ; CH2 of DCE
        opls_967   CLAA   17   35.45300   -0.227       A    3.16000e-01
         0.20920e+01 ; Cl of DCE

        *dce.pdb*

        HETATM    1 CLAA DCE     1       6.300  -2.280   1.360  1.00
        20.00            CL
        HETATM    2  CAB DCE     1       5.060  -3.540   1.500  1.00
        20.00             C
        HETATM    3  CAC DCE     1       4.320  -3.740   0.170  1.00
        20.00             C
        HETATM    4 CLAD DCE     1       3.270  -2.350  -0.210  1.00
        20.00            CL

        After adding all this, when i run grompp i get the error as
        *fatal error Unknown bond_atomtype CLAA*. can any one tell me
        why this happens?.


    Have you been sure to #include the correct (modified) force field
    files?  That is, if you made a local copy and adjusted them, these
    won't be the files that pdb2gmx will #include by default.

    -Justin

        Regards
        Vinoth


-- ========================================

    Justin A. Lemkul
    Ph.D. Candidate
    ICTAS Doctoral Scholar
    MILES-IGERT Trainee
    Department of Biochemistry
    Virginia Tech
    Blacksburg, VA
    jalemkul[at]vt.edu <http://vt.edu> | (540) 231-9080
    http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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--
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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