[gmx-users] problem in umbrella sampling

[Rajneet kaur Saini]

Dear Users,
hi.. i am following justin umbrella sampling tutorial.i dont understand the procedure for umbrella sampling after this command:
To extract the frames from your trajectory (traj.xtc), use trjconv (save the whole system, group 0, when prompted):trjconv -s pull.tpr -f traj.xtc -o conf.gro -sep
A series of coordinate files (conf0.gro, conf1.gro, etc) will be produced, corresponding to each of the frames saved in the continuous pulling simulation. To iteratively call g_dist on all of these (501!) frames that were generated, I have written a Perl script that takes care of this task. It will print a file called "summary_distances.dat" that contains this information. The script can be found here. We will need to make use of the index file again, as well as a text file called "groups.txt," which will be used to select our analysis groups non-interactively. The contents of groups.txt should be:19
20
The groups.txt file can be created with a plain text editor. Once you have this file, change the .txt file extension of distances.txt (linked above) to .pl and execute the script:perl distances.pl
Look at the contents of summary.dat to see the progression of COM distance between chain A and chain B over time. Make note of the configurations to be used for umbrella sampling, based on the desired spacing. That is, if you want 0.2-nm spacing, you might find the following lines in summary.dat:50     0.600
...
100    0.800
You would then use conf50.gro and conf100.gro as the starting configurations of two adjacent umbrella sampling windows. Make note of all the configurations you wish to use before continuing. For the purposes of this tutorial, identifying configurations with 0.2-nm spacing will suffice, although in the original work a different (more detailed) spacing was used.I am using Gromacs 5.0.5
Could anybody please explain me?????RegardsR.K