Justin, Thanks for your response. The membranes I've already run are made of POPC and cholesterol, so the sphingomyelin membrane is my next simulation but I haven't managed to find a proper forcefield for it. Would you know where to find this? Ramon
-----Original Message----- From: Justin A. Lemkul <jalem...@vt.edu> Reply-to: "jalem...@vt.edu" <jalem...@vt.edu>, Discussion list for GROMACS users <gmx-users@gromacs.org> To: Discussion list for GROMACS users <gmx-users@gromacs.org> Subject: Re: [gmx-users] g_density CHARMM Date: Tue, 11 Jan 2011 19:45:58 +0100 Ramon Guixà wrote: > > Dear all, > > I am just a newbie to Gromacs so sorry for being naive with my questions... > > I would like to yield electron density profiles out of different > trajectories of membranes simulated with NAMD and last CHARMM forcefield > (all_36_lipid_cholesterol). I first tried to use pdb2gmx in order to > generate a GROMACS topology file that I could use for generating the > .tpr file needed for g_density. Well, I did not manage but is this the > proper way though? Not likely. pdb2gmx is useful for creating topologies of macromolecules built of repeating units (i.e. proteins and polymers). For lipid bilayers, it is far more common to construct the topology as a set of #include statements, i.e.: #include (forcefield) #include "first_lipid_type.itp" #include "next_lipid_type.itp" etc. > Also, so far all my trajectories are .dcd files; does the g_density > function needs a .pdb file per frame? Otherwise, is it possible to > directly convert .dcd files into the gromacs .xtc ones? > Newer versions of Gromacs (>4.5) can read any file format that VMD can read, so conversion is not necessary, provided you have the VMD libraries installed. > On another note, would anyone know where could I get proper topology and > parameter files of sphingomyelin? > If you already ran the simulations, do you not already have this? With the information in Chapter 5 of the manual, you should be able to convert your topologies from whatever format you have it in into the one required by Gromacs. -Justin > Many thanks in advance! > > Ramon > -- ======================================== Justin A. Lemkul Ph.D. Candidate ICTAS Doctoral Scholar MILES-IGERT Trainee Department of Biochemistry Virginia Tech Blacksburg, VA jalemkul[at]vt.edu | (540) 231-9080 http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin ========================================
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