Actually I solved the problem, I did a mistake in the bond conversion. Actually I found the right formula:
k_gromacs = k_charmm**418.4**2 rising form the conversion from angstrom to nanometer.... ---------- Messaggio inoltrato ---------- Da: francesco oteri <francesco.ot...@gmail.com> Date: 08 marzo 2012 10:49 Oggetto: charm to gromacs A: Discussion list for GROMACS users <gmx-users@gromacs.org> Dear gromacs users, I am trying to convert a charmm style parameter file into gromacs. So I al trying to understand how converting the force constants from CHARMM to gromacs. Using the CHARMM27 force field as a reference, I've noticed that to convert the bond constant the following formula is supposed to be used: k_gromacs = k_charmm**4184**2 In fact if I try to convert the following line from par_all27_prot_lipid.prm charmm file: CEL1 CEL1 440.000 1.340 ! butene, yin,adm jr., 12/95 I obtain the right result ( 440.000*4184*2. = 368192.0) charmm27/ffbonded.itp CEL1 CEL1 1 0.134 368192.0 But to convert the angle constants I've to use the following formula: k_gromacs = k_charmm**4.184**2. how demostrated by the conversion of the following line: par_all27_prot_lipid.prm CEL1 CEL1 CTL2 48.00 123.50 ! from 2-butene, yin,adm jr., 12/95 into charmm27/ffbonded.itp CEL1 CEL1 CTL2 5 123.50 401.664 0.0 0.0 My question is: Why in the former case I need the constant 4184 while in the latter the constant 4.184 is supposed to be used? Am I miss something? -- Cordiali saluti, Dr.Oteri Francesco
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