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[lammps-users] LJ parames
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[lammps-users] LJ parames

From: "284237308@...1204..." <284237308@...1204...>
Date: Thu, 3 Aug 2017 11:39:33 +0800

Hello guys
    I'm all new here so I have a little stupid question for sigma and epsilon for LJ pair coefficients. In some papers, I find that they only give the whole epsilon and sigma between the molecules. However, when I write pair coeff command in lammps, it should be the epsilon and sigma between two atom types. For example, for water, it should be like,
TIP3P-E water
pair_style      lj/cut/coul/long 13.0 
bond_style      harmonic
angle_style     harmonic
kspace_style    pppm 1.0e-5
pair_coeff      1 1 0.0 0.0         #H-H
pair_coeff      2 2 0.102 3.188     #O-O
pair_coeff      1 2 0.0 0.0         #O-H
bond_coeff      1 450 0.9572        #H-O
angle_coeff     1 55 104.52         #H-O-H
    But the parameters for CH4 is written like epsilon=0.2937, sigma=3.73. I think it supposed to be three sets of epsilon and sigma for C-C, H-H and C-H.
    So how should I write lammps pair coeff commands correctly for CH4 with only one set of epsilon and sigma?
    Thanks a lot. I'm trying my best to learn everything I can.