How can I use the CLASS2 potential?

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1

Dear all,
I’m now calculating total energies and densities of some alkane
by lammps. And I wanna use the class2 potentials. But how can
I get the parameters for angle_style class2 command, bond_style
class2 command, dihedral_style class2 command and pair_style
lj/class2/coul/long command. Any one could tell me? Thank you so
much.
Regards,
Edw

2

Dear all,
I'm now calculating total energies and densities of some alkane
by lammps. And I wanna use the class2 potentials. But how can
I get the parameters for angle_style class2 command, bond_style
class2 command, dihedral_style class2 command and pair_style
lj/class2/coul/long command. Any one could tell me? Thank you so
much.

force field parameters are either in the published
literature or part if licensed simulation packages.

the procedure usually is opposite of what you are
trying to do. people usually look up a suitable parameter
set for the problem they are looking at and then
implement it using the available potential styles in
lammps or some other MD code.

there is not *the* set of parameters for a potential type.
for example, there easily over a hundred different parameter
sets for water molecules.

axel.

3

Dear Alex,

Thank you so much for your kind quick reply.
I know that the compass ff is not free. So I am
now thinking about using the pcff ff. I have used
the msi2lmp tool transfer the .car and .mdf file
the lammps data file. How could I know which
style of these parameters belong to? I don’t know
whether I know it correctly. Thanks.

The system contains 100 hexane moleculars.
Pair Coeffs
1 0.0540000000 4.0100000000
2 0.0540000000 4.0100000000
3 0.0200000000 2.9950000000
Bond Coeffs
1 1.5300 299.6700 -501.7700 679.8100
2 1.1010 345.0000 -691.8900 844.6000
3 1.1010 345.0000 -691.8900 844.6000
4 1.5300 299.6700 -501.7700 679.8100
Angle Coeffs
1 110.7700 41.4530 -10.6040 5.1290
2 107.6600 39.6410 -12.9210 -2.4318
3 110.7700 41.4530 -10.6040 5.1290
4 112.6700 39.5160 -7.4430 -9.5583
5 107.6600 39.6410 -12.9210 -2.4318
6 110.7700 41.4530 -10.6040 5.1290
7 112.6700 39.5160 -7.4430 -9.5583
Dihedral Coeffs
1 -0.1432 0 0 0 -0 0
2 0.0000 0 0 0 -0 0
3 0.0000 0 0 0 -0 0
4 0.0000 0 0 0 -0 0
5 -0.1432 0 0 0 -0 0
6 0.0000 0 0 0 -0 0
7 0.0000 0 0 0 -0 0
…

4

The msi2lmp tool creates ff coeffs for the class2
ff in LAMMPS. E.g. in the list below, the bond coeffs
are for bond_style class2.

Steve

5

Dear Steve,
I have compared the coeff param with manual.
Just you said, the bond coeffs et.al. are for
class2 ff. But I encounted another error after I
submitted it.
pair_style lj/class2 9.5
pair_modify tail yes
bond_style class2
angle_style class2
dihedral_style class2
improper_style class2
special_bonds lj/coul 0.0 0.0 1.0 dihedral yes

6

What's the error?

Steve