vinothkumar mohanakrishnan wrote:
Hi Justin

Thank you for your suggestion. I am doing equilibration of DCE (108 molecules) alone in a box and there is no water molecule inside the box. cant i use -DFLEXIBLE for DCE?. by the way i will try your suggestion about xmgrace.


In that case, -DFLEXBILE will have no effect. The bigger concern then is the potential stability issues of not using constraints and using a 2-fs timestep. It might be fine, but keep it in mind if you run into problems.

-Justin

Regards
Vinoth

On Thu, Oct 21, 2010 at 5:25 PM, Justin A. Lemkul <jalem...@vt.edu <mailto:jalem...@vt.edu>> wrote:



    vinothkumar mohanakrishnan wrote:

        Hi Justin

        Below is my nvt.mdp (nvt equilibration) file.i think probably
        you can have look at it and its not such big.

        define          =                 -DFLEXIBLE


    You should never run MD with flexible water.  All the water models
    included in Gromacs are meant to be rigid.  -DFLEXIBLE should only
    be used during EM.


integrator = md nsteps = 50000 dt = 0.002 nstxout = 100 nstvout = 100 nstenergy = 100 nstlog = 100 constraint_algorithm = shake constraints = none

    If you're not using constraints, then a 2-fs timestep might be too
    large.  If you encounter any later instability, this is likely the
    cause.


unconstrained_start = yes shake_tol = 0.0001 morse = no ns_type = grid nstlist = 5 rlist = 1.0 coulombtype = PME rcoulomb = 1.0 vdwtype = Cut-off rvdw = 1.0 pme_order = 4 fourierspacing = 0.16 pbc = xyz tcoupl = V-rescale tc-grps = system tau_t = 0.1 ref_t = 300 DispCorr = Ener gen_vel = yes gen_temp = 300 gen_seed = 173529 regarding the plot i too know that one should use Xmgrace to
        plot. In the pressure Vs time(lysozyme tutorial) you have got
        two graphs. i to got the pressure Vs time (black line graph) my
        question is how to get the running average ( red line) and
        plot?. does i need any command to get the running average?. any
        help is highly appreciated.


    Data -> Transformations -> Running averages

    -Justin

        Regards
        Vinoth


        On Thu, Oct 21, 2010 at 4:56 PM, Justin A. Lemkul
        <jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>> wrote:



           vinothkumar mohanakrishnan wrote:

               Hi justin

               I found what went wrong and i corrected my mdp file.now the
               system equilibrated to the desired temperature 300 K (plus r
               minus 30 K) is this ok?


           This is impossible to assess without seeing your .mdp
        settings.  A
           fluctuation of 10% is probably fine.


               Apart from that i want to know how you plot the average
        running
               pressure and density in your tutorial for lyzosyme
        (redline). i
               just  want to do that for DCE. any help is highly
        appreciated.


           Xmgrace.

           -Justin

               Regards
               Vinoth


               On Wed, Oct 20, 2010 at 5:33 PM, Justin A. Lemkul
               <jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>
               <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>>> wrote:



                  vinothkumar mohanakrishnan wrote:

                      Hi Justin

                      I corrected the mistake what you said and i am
        able to run
                      energy minimisation and equilibration. but when i
        view my
               em.gro
                      and equilibration.gro in VMD it seems to me that
        the bonds
                      between the atoms are broken in molecules.I used
        g_energy to
                      check weather the system has


                  VMD tries to guess where bonds should be, but does not
        always
               do a
                  good job. Your topology defines bonds.  These are the
        only bonds
                  that there will be.  None can be broken or formed in
        standard MD.


                      equilibrated to the required temperature (300K) i
        found
               that the
                      variation in the temperature was 100K (plus r
        minus) . i
               am not
                      able find out what went wrong. any help is highly
               appreciated.


                  Without seeing your .mdp file, there's no way to know.
         The
                  fluctuation does seem too high, though, unless your system
               really is
                  just that unstable.  Are other properties converged -
        potential
                  energy, density, etc?  What type of ensemble are you
        using?

                  -Justin

                      Regards
                      Vinoth


                      On Mon, Oct 18, 2010 at 6:09 PM, Justin A. Lemkul
                      <jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>
               <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>>
                      <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>
               <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>>>> wrote:



                         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>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>
               <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>>
                      <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>
               <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>>>
                             <mailto:jalem...@vt.edu
        <mailto:jalem...@vt.edu> <mailto:jalem...@vt.edu
        <mailto:jalem...@vt.edu>>
               <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>>
                      <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>>
               <mailto:jalem...@vt.edu <mailto:jalem...@vt.edu>
        <mailto: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>
        <http://vt.edu>
               <http://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
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                         ICTAS Doctoral Scholar
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                         Department of Biochemistry
                         Virginia Tech
                         Blacksburg, VA
                         jalemkul[at]vt.edu <http://vt.edu>
        <http://vt.edu> <http://vt.edu>
               <http://vt.edu> | (540)
                      231-9080
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jalemkul[at]vt.edu | (540) 231-9080
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