Dear gromacs users, <div>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.</div><div>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:</div>
<div><br></div><div>k_gromacs = k_charmm*<b>4184</b>*2</div><div>In fact if I try to convert the following line from par_all27_prot_lipid.prm charmm file:</div><div>CEL1 CEL1 440.000 1.340 ! butene, yin,adm jr., 12/95<br clear="all">
<div><br></div><div>I obtain the right result ( 440.000*4184*2. = 368192.0)</div><div>charmm27/ffbonded.itp CEL1 CEL1 1 0.134 368192.0 </div><div><br></div><div><br></div><div>But to convert the angle constants I've to use the following formula:</div>
<div><br></div><div>k_gromacs = k_charmm*<b>4.184</b>*2.</div><div><br></div><div>how demostrated by the conversion of the following line:</div><div><div><div><br></div><div>par_all27_prot_lipid.prm CEL1 CEL1 CTL2 48.00 123.50 ! from 2-butene, yin,adm jr., 12/95</div>
</div><div><br></div><div>into</div><div><br></div><div>charmm27/ffbonded.itp CEL1 CEL1 CTL2 5 123.50 401.664 0.0 0.0</div></div><div><br></div><div><br></div><div><br></div><div>My question is: </div>
<div><br></div><div>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?</div><br>
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