WCA potential


For WCA potential in lammps we have used
pair_style lj/cut 2.5

pair_modify shift yes
pair_coefficient 1 1 1.0 1.0 1.12246

Here i used pair_style with a cut off 2.5 and pair_modify command and after this used pair_coefficient command with a new cut off 1.12246 .Now question is that will the
cut off distance change from 2.5 to 1.12246 after using this command ? When we ran the simulation the results looked like it took the cut off as 2.5 and not 1.12246.

The reason I am asking is the following, in Binary WCA shifted potential there are three types of interaction potentials depending on the pair we choose (U_{11}, U_{12}, U_{22}}.
In these three potentials the cut off should also vary because the inter particle distances are different.
If we do not vary the cut off then for U_22 and U_12 (potentials) I will have a part even after the minimum value.
So if I use the following commands will it make sure that the cut off will be taken differently or will it just
consider 1.2246 as the cut off distance for all the pairs.

pair_style lj/cut 1.12246
pair_modify shift yes
pair_coefficient 1 1 1.0 1.0 1.12246
pair_coefficient 1 2 1.5 0.8 0.897968
pair_coefficient 2 2 0.5 0.88 0.9877648



When you specify a general cutoff in the pair_style, it gets used in all subordinate pair_coeff statements in which you do not specify a separate cutoff. If you provide a cutoff via “pair_coeff 1 1 sigma epsilon cutoff_s” you’ll use cutoff_s for 1-1 interactions but the pair_style cutoff for any other interactions.

Also, you should use the “pair_coeff” command instead of writing “pair_coefficient” everywhere.