Dear Justin, Thank you very much for your answer.
I specified each molecule individually in index file and I used trjconv -sep command to seperate the system each step (conf1.gro, conf2.gro, conf3.gro, conf4.gro). Then I used script that you suggested, it was as; groups=`grep "^\[" index.ndx | wc -l` for ((i=1; i<$groups; i++)); do echo $((i++)) $i | g_traj -s topol.tpr -f conf$i.gro -n index.ndx -ox coord.xvg -com; done and I obtained the center of mass of each molecule at each step in seperate files. For example; if the system has 5 molecules and the run has 4 steps, I obtain 20 seperate files. However, I want to collect the center of mass of all molecules at all steps in only a file as following example; step molecule index x y z 0 0 1.15126297 -0.83798647 0.58398923 0 1 0.68224833 0.74993176 1.84797615 0 2 2.97914942 0.11095256 2.61386881 0 3 4.65560905 -0.26363975 0.17970542 0 4 0.56267048 1.31953148 0.91372036 0 5 1.82333602 -1.24385819 1.63649468 1 0 1.15081591 -0.83159143 0.58321940 1 1 0.68357557 0.76482290 1.84911002 1 2 2.97913055 0.11320974 2.61105259 1 3 4.65727424 -0.26322810 0.17973330 1 4 0.56043944 1.32080373 0.90883115 1 5 1.82315477 -1.24656235 1.63910681 2 0 1.15238968 -0.82695173 0.58273344 2 1 0.68630303 0.77769022 1.85014673 2 2 2.97731032 0.11649037 2.61009124 2 3 4.65780877 -0.26399845 0.18205542 2 4 0.55785475 1.32480364 0.90410962 2 5 1.82237425 -1.25034522 1.64005468 3 0 1.15513001 -0.82180588 0.58414463 3 1 0.69432865 0.79014913 1.85176367 3 2 2.97255177 0.12185169 2.60981656 3 3 4.65625400 -0.26611685 0.18777379 3 4 0.55652912 1.33345131 0.89997690 3 5 1.82007758 -1.25560496 1.63930391 How can I do this by using shell script in gromacs? Sincerely yours, Akn. -- View this message in context: http://gromacs.5086.n6.nabble.com/mass-center-of-each-molecule-tp4999661p5000094.html Sent from the GROMACS Users Forum mailing list archive at Nabble.com. -- gmx-users mailing list gmx-users@gromacs.org http://lists.gromacs.org/mailman/listinfo/gmx-users * Only plain text messages are allowed! * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/Search before posting! * Please don't post (un)subscribe requests to the list. Use the www interface or send it to gmx-users-requ...@gromacs.org. * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists