[gmx-users] Nonbonded parameters

[Steven Neumann]

On Wed, Jun 12, 2013 at 12:45 PM, Mark Abraham <mark.j.abraham at gmail.com>wrote:

> grompp is just enumerating the possible combinations of parameters given
> your inputs. Whether any of those will be used in the simulation will
> depend on whether atoms of given types are close enough and not excluded.
>
> Mark


I understand...but why for 60 mer polypeptide there are 1830 nonbonded
interactions ?

>
>
> On Wed, Jun 12, 2013 at 12:40 PM, Steven Neumann <s.neumann08 at gmail.com
> >wrote:
>
> > I got it. However,
> >
> > I have 60  atoms in my chain all with given C6 and C12 with a combination
> > rule 1. When running grompp:
> >
> > Generated 1830 of the 1830 non-bonded parameter combinations
> > Generating 1-4 interactions: fudge = 1
> > Generated 1830 of the 1830 1-4 parameter combinations
> > Excluding 3 bonded neighbours molecule type 'Protein_chain_X'
> > Analysing residue names:
> > There are:     1    Protein residues
> > Analysing Protein...
> > Number of degrees of freedom in T-Coupling group rest is 118.00
> > This run will generate roughly 2 Mb of data
> >
> > when changing nrexcl in my topology to 0:
> >
> >
> > Generated 1830 of the 1830 non-bonded parameter combinations
> > Generating 1-4 interactions: fudge = 1
> > Generated 1830 of the 1830 1-4 parameter combinations
> > Excluding 0 bonded neighbours molecule type 'Protein_chain_X'
> > Analysing residue names:
> > There are:     1    Protein residues
> > Analysing Protein...
> > Number of degrees of freedom in T-Coupling group rest is 118.00
> > This run will generate roughly 2 Mb of data
> >
> > So if I exclude 1-3 interactions I have the same number of nonbonded
> > parameters as well as 1-4 interactions. Can someone explain me this
> please?
> >
> >
> >
> > On Wed, Jun 12, 2013 at 11:12 AM, Steven Neumann <s.neumann08 at gmail.com
> > >wrote:
> >
> > >
> > >
> > >
> > > On Wed, Jun 12, 2013 at 11:05 AM, Justin Lemkul <jalemkul at vt.edu>
> wrote:
> > >
> > >>
> > >>
> > >> On 6/12/13 6:00 AM, Steven Neumann wrote:
> > >>
> > >>> Thank you. That means that e.g. when two LJ atoms of a different type
> > >>> approaching each other the non bonded LJ potential energy is a sum of
> > two
> > >>> potentials of those atoms?
> > >>>
> > >>>
> > >> No, please refer to the Gromacs manual for discussion on "combination
> > >> rules" and how they fit into the Lennard-Jones equation.
> > >>
> > >> -Justin
> > >>
> > >
> > > I read it.
> > > I used combination rule 1 in which C=4epsSig^6 and A=4epsSig^12 - So
> that
> > > means that when you provide in [atomtypes] in ffnonbonded your C and A
> > > values each atom has a specific LJ potential shape. Right?
> > > So two of them approaching each other in my system will have have the
> sum
> > > of it.
> > >
> > > Steven
> > >
> > >
> > >
> > >>
> > >>
> > >>> On Wed, Jun 12, 2013 at 10:44 AM, Justin Lemkul <jalemkul at vt.edu>
> > wrote:
> > >>>
> > >>>
> > >>>>
> > >>>> On 6/12/13 5:30 AM, Steven Neumann wrote:
> > >>>>
> > >>>>  Dear Gmx Users,
> > >>>>>
> > >>>>> Please, correct me if I am wrong. In ffnonbonded.itp
> > >>>>>
> > >>>>> [ atomtypes ] - these are nonbonded parameters between atoms of the
> > >>>>> same
> > >>>>> type
> > >>>>>
> > >>>>>
> > >>>> No, these are the nonbonded parameters that are used when applying
> > >>>> combination rules between any atoms.
> > >>>>
> > >>>>
> > >>>>   [ nonbond_params ] these are nonbonded parameters between atoms of
> > >>>>
> > >>>>> different type
> > >>>>>
> > >>>>>
> > >>>> No, these override combination rules.
> > >>>>
> > >>>>
> > >>>>   [ pairtypes ] - 1-4 interactions
> > >>>>
> > >>>>>
> > >>>>> If that is correct why amber force filed has only [atomtypes]
> column?
> > >>>>> How
> > >>>>> nonbonded parameters are calculated between atoms of a different
> > type?
> > >>>>> The same with charmm - only [atomtypes ] and [pairtypes ] are
> > provided.
> > >>>>> Would you please explain?
> > >>>>>
> > >>>>>
> > >>>>>  Gromos force fields, for instance, have complex ways of generating
> > >>>> nonbonded interactions that are not always the same for a given
> > >>>> atomtype.
> > >>>>   Other force fields just use straight combination rules and thus
> > never
> > >>>> need
> > >>>> [nonbond_params].
> > >>>>
> > >>>> -Justin
> > >>>>
> > >>>> --
> > >>>> ==============================****==========
> > >>>>
> > >>>>
> > >>>> Justin A. Lemkul, Ph.D.
> > >>>> Research Scientist
> > >>>> Department of Biochemistry
> > >>>> Virginia Tech
> > >>>> Blacksburg, VA
> > >>>> jalemkul[at]vt.edu | (540) 231-9080
> > >>>> http://www.bevanlab.biochem.****vt.edu/Pages/Personal/justin<
> > http://vt.edu/Pages/Personal/justin>
> > >>>> <h**ttp://www.bevanlab.biochem.vt.**edu/Pages/Personal/justin<
> > http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin>
> > >>>> >
> > >>>>
> > >>>> ==============================****==========
> > >>>>
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> > >> --
> > >> ==============================**==========
> > >>
> > >> Justin A. Lemkul, Ph.D.
> > >> Research Scientist
> > >> Department of Biochemistry
> > >> Virginia Tech
> > >> Blacksburg, VA
> > >> jalemkul[at]vt.edu | (540) 231-9080
> > >> http://www.bevanlab.biochem.**vt.edu/Pages/Personal/justin<
> > http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin>
> > >>
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