VMD-L Mailing List
From: Axel Kohlmeyer (akohlmey_at_gmail.com)
Date: Thu Feb 04 2010 - 05:11:59 CST
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On Wed, Feb 3, 2010 at 12:21 PM, Jelle van Sijl <j.vansijl_at_gmail.com> wrote:
> Dear All,
dear jelle,
> I would like to compute the molecular dipole moment for a given
> selection of atoms. The IONS+CENTERS.xyz file contains 4 Wannier centers
> per H2O molecule identified by atom name "X".
please keep in mind that the vast majority of people here still
don't have a clue what you are after with the kind of information
that you provide. i assume that you are asking about a file generated
by a CPMD calculation.
> I've searched the vmd list archive and so far came up with creating a
> user field selection of WFC values:
i don't quite understand what this would supposed to be doing.
> package require pbctools
> set mol [mol new {GEOM.xyz} waitfor all]
> mol addfile {IONS+CENTERS.xyz} waitfor all
where is the GEOM.xyz file coming from? it should not
be needed, since the IONS+CENTERS.xyz file is effectively
self-contained.
> set mol [molinfo top]
> pbc set {12.50 12.50 12.50} -all
>
> set xsel [atomselect $mol "name X"]
> set nf [expr [molinfo $mol get numframes] - 1 ]
> set nx [$xsel num]
> set fp [open "WANNIER_CENTER" "r"]
why do you read the WANNIER_CENTER file if you
have already read in the IONS+CENTERS.xyz which
contains the positions of the wannier centers and the
spread contained in add the WANNIER_CENTERS file
is irrelevant for the calculation of the dipole moment.
> for {set f 0} {$f < $nf} {incr f} {
> set ul {}
> for {set i 0} {$i < $nx} {incr i} {
> gets $fp line
> lappend ul [lindex $line 1 2 3 4]
this line doesn't make any sense at all. its result will
be empty. check the tcl documentation of the lindex command.
> }
> $xsel frame $f
> $xsel set user $ul
> }
> close $fp
>
>
> which gives the following error message:
> atomsel: set: bad data in 0th element
no surprise about this error. see my comment above.
> How can I select the right WFC's given a selection of atoms?
there is no generic answer to this question. in some cases, you
simply cannot (e.g., when you have a non-polar bond, where two
atoms share the wannier centers). if your atom selection contains
a full molecule, the wannier centers should be closer to the non-wannier
center position than a typical bond to a hydrogen, so a selection of
"name X and within 1.0 of (within 1.1 of index 0)" should select the
wannier centers that belong to the first water molecule (assuming the
elements in the IONS+CENTERS.xyz are ordered as O O H H H H).
> Once I have the WFC's in a selection, how can I use vmd to combine these
> with the ion positions such that I get the average dipole moment per
> H2O?
this is actually not really a VMD question, and you can answer
it easily for yourself if you answer the following questions.
what does a wannier center stand for? and how do you compute
a molecular dipole moment from a classical charge distribution?
then just have a look at the VMD documentation.
cheers,
axel.
> Thanks in advance & kind regards,
> Jelle van Sijl
>
>
>
>
> --
> Jelle van Sijl, MSc.
> PhD student, Department of Petrology
> Faculty of Earth and Life Sciences (FALW)
> VU University Amsterdam, De Boelelaan 1085
> 1081 HV Amsterdam, The Netherlands
> Phone +31 (0)20 5983725
> http://www.falw.vu.nl/petrology
>
>
>
-- Dr. Axel Kohlmeyer akohlmey_at_gmail.com Institute for Computational Molecular Science College of Science and Technology Temple University, Philadelphia PA, USA.
- Next message: Joshua Anderson: "Re: Trouble building VMD 1.8.7 on Mac OS X"
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- In reply to: Jelle van Sijl: "molecular dipole moment"
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