Hi, The gro file format, just like the pdb format, is an ancient fixed format. Thus it supports only 3 decimals. Note that this has nothing to do with single or double precision (which have a range of rougly 10^7 and 10^16).
If pdb2gmx does not mess with your hydrogen and terminal atom coordinates (as some old versions did), you can use pdb2gmx -o conf.pdb for pdb coordinate output or -o conf.g96 for lots of decimals. All Gromacs programs can read pdb and g96 instead of gro files. Berk From: alanwil...@gmail.com Date: Wed, 28 Jul 2010 07:45:50 +0100 To: gmx-users@gromacs.org Subject: [gmx-users] Re: gromacs energies very different from other MD engine for the very same system and condition First of all, thanks a lot guys, in special Ilja and Chris. Indeed, Ilja's observation proved to be corrected, and as Chris suggested, using the pdb instead of the gro for grompp and the energies matched. However, I am still uneasy with the fact that pdb2gmx_d and mdrun_d is not generating a gro with at least 6 decimals instead of the usual 3. Many thanks, Alan On Tue, Jul 27, 2010 at 20:34, <gmx-users-requ...@gromacs.org> wrote: Alan: you should try Ilja's suggestion, it was a good one. The idea is that during pdb2gmx you may have obtained a .gro file that was rounded and then you may have used this .gro as input to grompp and so your run did not start with the exact same coordinates in gromacs and namd. A similar test would be to be sure that you run grompp with the same .pdb file that you used in namd, etc. (or perhaps you already did that?) Actually, from what you post below I think that you have your answer. Use the orig .pdb into grompp and things should be ok, probably even in single precision, although the output .gro will be rounded as you see. PS: let's keep a positive mood. Chris. -- Alan Wilter S. da Silva, D.Sc. - CCPN Research Associate Department of Biochemistry, University of Cambridge. 80 Tennis Court Road, Cambridge CB2 1GA, UK. >>http://www.bio.cam.ac.uk/~awd28<< -- 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/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/mailing_lists/users.php
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