[gmx-users] Possible trjconv malfunction?

[Nathan Scott]

Hi all,

I am trying to use trjconv to extract .g96 files iteratively, then use my
own software for analysis, then delete the .g96 file, but I am running into
perplexing behavior. I did a bit of searching in the list archive but can
find no mention of this, so it could well be I am just doing something
wrong.

I have a continuation (the original simulation was run for 20 ns) of a
simulation that was run for 50,000 steps, dt=0.002 ps, with the xtc file
written every 1000 steps (2 ps). When I issue the following command
everything works fine and I get a .g96 file ad the header shows a time of
20000.

echo 0|trjconv_mpi -f stn_wt_a_fit_1.xtc -s stn_wt_a_1.tpr -b 20000 -e
20000 -o g96/stn_wt_a_1_0.g96 -novel

But when I try to extract the next file, which should be 2 ps later in the
simulation by using this command, I get an error:

echo 0|trjconv_mpi -f stn_wt_a_fit_1.xtc -s stn_wt_a_1.tpr -b 20002 -e
20000 -o g96/stn_wt_a_1_0.g96 -novel

WARNING no output, last frame read at t=20004

When I run with -b and -e set to 20004 I get a .g96 file with a time of
20004. I tried 20001, 20002, and 20003 just to see what happens, and I get
the same error referencing 20004 as the "last frame read."

trjconv seems to think that there are 4 ps between frames. Just to check
myself, I did a gmxdump of the .xtc file and the .edr file, and they both
show a frame at 20002 ps and a final frame of the trajectory at 20100,
exactly as I expected, .Also, when I use trjconv -sep to output all of the
individual frames of the trajectory in one shot, I get 51 files with
correct timings in the headers, 20000, 20002, 20004, etc up to 20100.

If anyone could shed light on this problem I would very much appreciate it.
This is Gromacs 4.6.5, by the way, being run on Trestles at the SDSC
through an XSEDE account. I am running into problems trying to extract all
of the structure files at once to the per-node scratch space so I thought
I'd give iterative extraction a try, since my analysis code runs in serial
anyway.

Thanks in advance for any help!

Best Wishes,
Nathan