VMD-L Mailing List

From: Stefan Doerr (stefdoerr_at_gmail.com)
Date: Thu Apr 02 2015 - 07:08:33 CDT

Right, but I don't think this covers my problem. If you look at the water
box atoms in the PDB
(which is by the way the exact water box VMD uses for solvating) a unique
resid is correctly assigned to the 3 atoms of each
water molecule. The segid is also correctly assigned to only the water box.
Hence the segid and resid combination in the selection is unique.

In that case using "segid WT5 and same residue" should be equivalent to
"segid WT5 and same resid".
We are not talking about the absolute values of resid or residue but about
the "same" resid or residue inside a segment.

On Thu, Apr 2, 2015 at 1:54 PM, Axel Kohlmeyer <akohlmey_at_gmail.com> wrote:

> On Thu, Apr 2, 2015 at 4:41 AM, Stefan Doerr <stefdoerr_at_gmail.com> wrote:
> > Hello,
> > I wanted to point out what looks like an atomselect bug to me.
> >
> > I have a lipid membrane system with a protein and I added a water box on
> it
> > which clashes with the membrane and protein.
> >
> > I am trying to select all water atoms that clash with non-water atoms to
> > remove them.
> > Given the following two selections I would expect identical results (as
> long
> > as the water molecules have correct resid's in the PDB which they indeed
> > have):
> >
> > segid WT5 and same residue as (within 2.4 of not segid WT5)
> > segid WT5 and same resid as (within 2.4 of not segid WT5)
> >
> > I made a imgur album with some explanatory pictures
> > http://imgur.com/a/RfPMq
> >
> > The first selection seems to works fine (see album: red balls). If you
> > change residue to resid it wrongly finds many more water molecules
> (yellow
> > balls). Although I actually have the impression that the first selection
> is
> > not totally correct either. I have seen it remove only pieces of a water
> > molecule and not all of it.
> >
> > I don't see a reason why resid should not work in this selection exactly
> > like residue.
>
> residue is a number designated by VMD and guaranteed to be unique,
> resid is just a label imported from the PDB file and can repeat. as
> far as i remember, the PDB standard only requires it to be unique
> within a segment.
>
> however, since residue is still dependent on a correct assignment of
> residue labels, i.e. resids to molecules, the safest way to select
> whole molecules is to use "same fragment as". fragment is also a
> property computed by VMD and assigns a unique id to each
> group/fragment of connected atoms, which coincides with molecules in
> classical force fields (that is assuming that you have correct bond
> information imported from a .psf file or similar).
>
> axel.
>
>
> >
> > Here is the PDB file if you want to test it. I tested it with 1.9.1 and
> > 1.9.2 VMD:
> > https://www.dropbox.com/s/o117eo5lpxmsp9e/onlyWT5andrest.pdb?dl=0
>
>
>
> --
> Dr. Axel Kohlmeyer akohlmey_at_gmail.com http://goo.gl/1wk0
> College of Science & Technology, Temple University, Philadelphia PA, USA
> International Centre for Theoretical Physics, Trieste. Italy.
>