sreelakshmi ramesh wrote:
Do u mean to say that all the force fields available in gromacs are default to be used only for LJ potential.


Yes.  That's why they all have their [defaults] directives set to use LJ.

-Justin

On Wed, Dec 22, 2010 at 9:32 AM, Justin A. Lemkul <jalem...@vt.edu <mailto:jalem...@vt.edu>> wrote:



    sreelakshmi ramesh wrote:

        Dear justin,
                        I am sorry the file is ffG43a1nb.itp.It
        <http://ffG43a1nb.itp.It> <http://ffG43a1nb.itp.It> was a typing
        mistake.


    The points I raised before still stand:

    1. You're not using 43A1, you're using ffgmx, according to that
    message from grompp.

    2. You can't make a simple change to any of the force fields
    included in Gromacs to magically convert them into using Buckingham
    potentials.  None of them were designed to do that.  You'll have to
    basically re-write the entirety of the ff*nb.itp file, and then
    validate that such a force field model is even valid, because none
    of them were parameterized to be.

    -Justin

        On Wed, Dec 22, 2010 at 9:26 AM, Justin A. Lemkul
        <jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>> wrote:



           Justin A. Lemkul wrote:



               sreelakshmi ramesh wrote:

                   I am using gromos force field fotr my work and This force
                   field's files come filled
                    with LJ  functions and now if i want to work with
                   buckingham potential i changed in default section of
        force
                   field ffG34a21.itp file but it gives me the follwing
        errors


                   ERROR 77 [file ffgmxnb.itp, line 144]:
                    Trying to add LJ (SR) while the default nonbond type is
                   Buck.ham (SR)


           I should also add that if you think you're using Gromos96
        (although
           from "ffG34a21.itp" it's not at all clear to me that you're using
           any legitimate form of it - 43A1? 43A2? something else?), you're
           not.  The "ffgmx" force field is a modified form of Gromos87
        that is
           antiquated and should not be used for new simulations, as
        described
           in detail in the manual.

           -Justin


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

           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> <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 <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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