Dear all,

I was wondering whether someone could possibly clarify the situation with setting a cutoff for lj potential as follows:

pair_style lj/cut 1.4

pair_modify shift yes

# pair_coeff for lj/cut, specify 4:

# * atom type interacting with

# * atom type

# * epsilon (energy units)

# * sigma (distance units)

pair_coeff 1 1 1.0 1.0

Do I understand correctly that in this situation, we set the cutoff at 1.4 and after that potential energy does not change as a function of r(sigma) and stays as it was at the cutoff? Or in a different possible scenario, as soon as the curve reaches the 1.4 cutoff, does it go down to the value specified by the well depth (epsilon)?

Thank you very much for any input in advance.

With best wishes,

Anna

Dear all,

I was wondering whether someone could possibly clarify the situation

with setting a cutoff for lj potential as follows:

pair_style lj/cut 1.4

pair_modify shift yes

# pair_coeff for lj/cut, specify 4:

# * atom type interacting with

# * atom type

# * epsilon (energy units)

# * sigma (distance units)

pair_coeff 1 1 1.0 1.0

Do I understand correctly that in this situation, we set the cutoff at

1.4 and after that potential energy does not change as a function of

r(sigma) and stays as it was at the cutoff? Or in a different possible

scenario, as soon as the curve reaches the 1.4 cutoff, does it go down

to the value specified by the well depth (epsilon)?

neither.

with pair_modify shift yes. the potential energy at the cutoff is being

computed and then *always* subtracted from the potential energy,

i.e. the entire potential curve is shifted so that the potential is 0.0

at the cutoff radius.

it is easy to see this from looking at the pair_lj_cut.cpp source file.

axel.