Dear lammps users,
I want to use the Morse bond parameters to describe the separation of the linked atoms when both the atoms are under big tensile force using the CVFF force field. And, as far as my know, The the energy Function of atom bond in CVFF force field is Morse type, which need three parameters(http://lammps.sandia.gov/doc/bond_morse.html)) to specify. However, I can’t obtain the three Morse bond parameters using the msi2lmp tool to translate the MS model to LAMMPS data file, and the number of the obtained bond parameters in the data file is two, indicating the bond style is harmonic, not Morse bond. So, my question is how I can get the three Morse bond parameters, and how the other lammps users get the information of Morse bond parameters.
Besides, I have another problem. In the CVFF force field, the function term of vdW is ξ[(σ/r)^12-2(σ/r)^6], but I couldn’t find the Pair_style with the function term. The function term I’m using is 4ξ[(σ/r)^12-(σ/r)^6] with the pair_style lj/cut, and the improper function induce the lattice parameters expand bigger than the real, And my second question is how the lammps users usually deal with the problem of missing the proper potential function.
Thanks a lot.
Best wishes
D. Chai
Dear lammps users,
I want to use the Morse bond parameters to describe the separation of
the linked atoms when both the atoms are under big tensile force using the
CVFF force field. And, as far as my know, The the energy Function of atom
bond in CVFF force field is Morse type, which need three
CVFF offers both options, harmonic or morse.
parameters(http://lammps.sandia.gov/doc/bond_morse.html) to specify.
However, I can't obtain the three Morse bond parameters using the msi2lmp
tool to translate the MS model to LAMMPS data file, and the number of the
the authors of msi2lmp chose to output harmonic bond parameters rather
than mores.
obtained bond parameters in the data file is two, indicating the bond style
is harmonic, not Morse bond. So, my question is how I can get the three
Morse bond parameters, and how the other lammps users get the information of
Morse bond parameters.
you have to either look them up in the force field parameter file or
modify msi2lmp to output morse parameters instead of harmonic.
Besides, I have another problem. In the CVFF force field, the function
term of vdW is ξ[(σ/r)^12-2(σ/r)^6], but I couldn't find the Pair_style with
the function term. The function term I'm using is 4ξ[(σ/r)^12-(σ/r)^6] with
the pair_style lj/cut, and the improper function induce the lattice
those two functional forms are the same! they just have different
conventions of how sigma is defined (minimum of potential vs.
potential = zero). msi2lmp outputs those parameters correctly.
parameters expand bigger than the real,
that is most certainly a misinterpretation of your results.
And my second question is how the
lammps users usually deal with the problem of missing the proper potential
function.
every force field has a "recipe" for how parameters are derived. this
is described in detail in the publication(s) of the definition of the
force field and its parameter sets. force field parameterization is a
bit of a black art and requires practice and a good understanding of
the process and MD in general.
axel.