Question: VMD : Lammps-data I/O

Dear Lammps members,

I would like select a particular frame within VMD and write the data to a file.

The file I am reading into VMD is from lammps output of “custom” format

" id type mass x y z vx vy vz" — outputing position and velocity of atoms

Dear Lammps members,

I would like select a particular frame within VMD and write the data to a
file.

why on earth do you address a VMD question to the lammps-users forum?
your chances to get a reasonable answer are massively smaller (what
are the chances that there are any VMD experts here compared to the
VMD-l mailing list?).

The file I am reading into VMD is from lammps output of "custom" format
" id type mass x y z vx vy vz" --- outputing position and velocity of
atoms

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1.
I am able to select a frame inside VMD by deleting the rest of the frames.
Is there a better way to do select a frame ?

yes. you just select the frame you want to write out. you can select
it right from the save dialog and also from the script interface. it
is all explained in the user's guide. that what user's guides are for.

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2.
Then I used "topo writelammpsdata ..." command to write out the data in that
chosen frame.

However, only the "x y z " position data is written out, but the "vx vy vz"
velocity data
in the lammps file is not written.

yes. that is correct and intentional.

Is there a way write out both position and velocity data out to file ?

why go the complicated route via VMD? you can just use LAMMPS and
read_dump and write_data commands.

axel.