Hello, I wish to compute rdf of Na+ ions around protein surface. I use the command: g_rdf -f traj.xtc -n index.ndx -o rdf_prot_Na_res_com.xvg -b 40000 -s md.tpr -surf mol -rdf res_com -bin 0.01
Since when -surf option is used, g_rdf does not normalize the rdf, I am curious what does actually g_rdf reports in the output .xvg file? If we refer to the Eq. (8.3) of gromacs_manual.pdf, which of the following value gets reported in the output file: 1) \sum_{1,N_B} (\delta(r_{i,j}-r)) 2) \sum_{1,N_B} (\delta(r_{i,j}-r)) / (4*pi*r^2) 3) \sum_{1,N_B} (\delta(r_{i,j}-r)) / (4*pi*r^2) / N_A My hunch is that g_rdf -surf reports value calculated by Eq. 1 since computing the term (4*pi*r^2) for an irregular surface is very complex. Please advise ? My second question is regarding the value of r_max. In the manual, it's reported: Usually the value of rmax is half of the box length. When I compute rdf using g_rdf -surf option, the value of maximum r is indeed half the box length. However, I think the value of r_max, when -surf is used, should be considerably less than the (box length)/2. If I am right, in this case, r is the distance from the surface of the protein and not from the center of the protein. Hence, r_max should be around the length of solvent padding from protein surface. Thanks, Neeraj -- View this message in context: http://gromacs.5086.n6.nabble.com/g-rdf-surf-rdf-res-com-details-needed-tp4908525p4908525.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 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