Dear Justin,
I have calculated upon the way you provided as follows : CHARMM Rmin/2 -> Gromacs sigma: multiply by 2 to get Rmin, convert to sigma by multiplying by 2^(-1/6), then multiply by 0.1 to convert A -> nm Sigma = 3.83 Rmin = (3.83 * 2) 7.66 * 2^(-1/6)*0.1 = 0.682428418 Epsilon: multiply the CHARMM value by 4.184 to convert kcal/mol to kJ/mol Epsilon 0.0262 x 4.184 = 0.1096208 Is that right conversion?, if so, I have used g_sigeps utility in gromacs for above mentioned sigma and epsion values and got entirely different values: g_sigeps -sig 3.83 -eps 0.0262 c6 = 3.30791e+02, c12 = 1.04411e+06 sigma = 3.83000, epsilon = 0.02620 Van der Waals minimum at 4.29903, V = -0.0262 Fit of Lennard Jones (12-6) to Buckingham: A = 4264.18, B = 2.79133, C = 330.791 Please advice if i am making any mistake ? On 5/31/14, 8:43 AM, ????? wrote: > Dear justin, > > Could tell me how do I convert those non-bonded values between CHARMM and > gromos431 ? > > I am unaware of this conversion. > Just for clarity, converting between CHARMM FF parameters to the Gromos FF will result in a junk simulation. Converting CHARMM units for use in Gromacs software (note the difference between Gromos and Gromacs!) is simple: CHARMM Rmin/2 -> Gromacs sigma: multiply by 2 to get Rmin, convert to sigma by multiplying by 2^(-1/6), then multiply by 0.1 to convert A -> nm Epsilon: multiply the CHARMM value by 4.184 to convert kcal/mol to kJ/mol -Justin -- Gromacs Users mailing list * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting! * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists * For (un)subscribe requests visit https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or send a mail to gmx-users-requ...@gromacs.org.