[gmx-users] Problems about sigma & epsilon to C6 & C12 LJ-parameters conversion

[james zhang]

Hi,

I am trying to do some simulation of chloroform system and I need convert
sigma & epsilon to C6 & C12 LJ-parameters.

I use C6=4*epsilon*sigma^6 and C12=4*epsilon*sigma^12 formula.
This is my result

[ atomtypes ]
;type    mass    charge       ptype          sigma      epsilon
 CH      12.01100   0.420       A        3.80000e-01  3.26944e-01
 CLCL3   35.45300  -0.140       A        3.47000e-01  1.25604e+00

[ atomtypes ]
;name  at.num      mass        charge   ptype       c6           c12
   CH    6      13.01100       0.000       A   0.39376E-02   0.11856E-06
  CL3   17      35.45300       0.000       A   0.87710E-02   0.15300E-06


The sigma and epsilon LJ-parameters is very good to discribe chloroform box
in the molecular topology of user contributions.
http://www.gromacs.org/component/option,com_docman/task,cat_view/gid,36/dir,DESC/order,name/limit,5/limitstart,10/
But when I use C6&C12 LJ-parameters I can not get equilibrium and the
moleculars sticked together.

Thanks in advance.

-- 
Sincerely yours,
James Jianzhang
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