Hello, LAMMPS users,

I checked my simulation. It looked some atoms were overlapped. However, the vdw interaction looked fine. Therefore, I would like to explicitly check the vdw interaction between one pair of atoms. In my input script, I defined several variable. It seemed I can’t do calculation such as sub (I can output the coordinates of those two particles). Could you please help me find where I have a mistake. The relevant part of my script is as following:

group 1 id 265 305

variable stepi equal step

variable x1 equal x[265]

variable x2 equal x[305]

variable y1 equal y[265]

variable y2 equal y[305]

variable dx equal sub({x1}, {x2})

variable dy equal sub({y1}, {y2})

variable distance equal sqrt(add(mult(sub(x[305], x[265]), sub(x[305], x[265])), mult(sub(y[305], y[265]), sub(y[305], y[265]))))

variable LJ_pair equal evdwl

compute 2 1 variable LJ_pair

compute 3 1 variable distance

fix 4 1 print 100 “checkDistance {stepi} {x1} {x2} {y1} {y2} {distance} {dx} {dy}”

Thank you for help!

Dongsheng