question about improper coefficient

Hi
We have been trying to use Lammps to do the simulation. The structure we use is polymer with nanotube. We have some doubt in the parameters. As for the improper turn, we use umbrella, for which the formula is image.png
Here we use the real units, and the unit for K(energy) is Kcal/mol. However, when we go to check the parameters in Mayo’s paper, we find that the K=40(Kcal/mol)/rad^2. As the unit of K is different from the paper and what we have here, we wonder if there is any way to convert the K in the paper to fit the formula we have here?
Plus, as for the harmonic improper style, how can we get the value of the parameter K and X0?

Hi
We have been trying to use Lammps to do the simulation. The structure we use is polymer with nanotube. We have some doubt in the parameters. As for the improper turn, we use umbrella, for which the formula is image.png
Here we use the real units, and the unit for K(energy) is Kcal/mol. However, when we go to check the parameters in Mayo’s paper, we find that the K=40(Kcal/mol)/rad^2. As the unit of K is different from the paper and what we have here, we wonder if there is any way to convert the K in the paper to fit the formula we have here?
Plus, as for the harmonic improper style, how can we get the value of the parameter K and X0?

i don’t understand your question. what style of improper was used in your reference paper?
you have to use the same style in LAMMPS. perhaps it is named differently. the parameter
of K is specific to the style.

axel.

See the improper harmonic command in LAMMPS. It is K chi^2 which
is K multiplied directly times an angle, so that K is units of energy/radian^2.

But in the formula you list the cos() terms are unitless so K has
to have units of just energy.

Steve

image.png