suitable forcefield

Hi dears
Good afternoon
My thesis is on the adsorption of three organic aromatics(Benzene ,
Toluene and P-xylene)
Incliding the Intramolecular Potentials (Bond Stretching,Angle Bending and
the Dihedral Angle),
I found from an article the potential parameters for such aromatics , but
they used

to compute angle interactions between triplets of atoms
and
                  Vb = K1(θ - θᵒ)^2 - K2(θ - θ0)^3

to compute dihedral interactions between quadruplets of
atoms
                   V(ϕ) = K3[1 - cos3(ϕ - ϕ0)]

such formulas are not included exactly in LAMMPS manual but I think that
the "angle_style quartic" and "dihedral_style class2" included in LAMMPS
manual can plays the role by some modifications and neglecting some

would u please guide me??
thx a lot

Hi dears
Good afternoon
My thesis is on the adsorption of three organic aromatics(Benzene ,
Toluene and P-xylene)
Incliding the Intramolecular Potentials (Bond Stretching,Angle Bending and
the Dihedral Angle),
I found from an article the potential parameters for such aromatics , but
they used

to compute angle interactions between triplets of atoms
and
                  Vb = K1(θ - θᵒ)^2 - K2(θ - θ0)^3

to compute dihedral interactions between quadruplets of
atoms
                   V(ϕ) = K3[1 - cos3(ϕ - ϕ0)]

such formulas are not included exactly in LAMMPS manual but I think that
the "angle_style quartic" and "dihedral_style class2" included in LAMMPS
manual can plays the role by some modifications and neglecting some
>>>
would u please guide me??

this is more a question that needs to be directed at an adviser than a
mailing list. which functional forms LAMMPS provides, is documented in
the manual. since you have already researched it and apparently found
that you have found parameters of a CLASS2 force field, there is not
much else to advise on this side.
to make certain that it works correctly is your task and it is the
task of your adviser to oversee that you are doing that correctly.

axel.

to compute angle interactions between triplets of atoms
and
                  Vb = K1(θ - θᵒ)^2 - K2(θ - θ0)^3

to compute dihedral interactions between quadruplets of
atoms
                   V(ϕ) = K3[1 - cos3(ϕ - ϕ0)]

such formulas are not included exactly in LAMMPS manual but I think that
the "angle_style quartic" and "dihedral_style class2" included in LAMMPS
manual can plays the role by some modifications

angle_style quartic and dihedral_style class2 should work

But I recommend "dihedral_style fourier".

To use that style, you will need to compile LAMMPS with the USER-MISC
package enabled. (This means you must go to the "src" directory and
type "make yes-user-misc" into the shell before compiling LAMMPS. I
wish they would take dihedral fourier out of USER-MISC.)

(Details: I would recommend "dihedral_style fourier" over
"dihedral_style class2" (or perhaps dihedral_style charmm). Both
"fourier" and "charmm" both use a much simpler function (and I think
they are faster to compute as a result). (However I recommend
"fourier" because I think "dihedral_style charmm" restricts you to
using one of the "charmm" pair styles as well.))

You can also always use "angle_style table" and "dihedral_style
table", if later on you need a more complex force-field. They should
be fast.