[lammps-users] neighbor list construction


I am trying to understand the neighbor list construction using a very
simple 3 atom system.
All atoms are of the same type and on the x-axis at x = -1, 0 , 1

The box is set as:
-10.0 10.0 xlo xhi
-10.0 10.0 ylo yhi
-10.0 10.0 zlo zhi

only energy terms are harmonic bond and LJ specified by :
Pair Coeffs
1 1000.0 5
Bond Coeffs
1 100.00 1.000

and the pair style is 'pair_style lj/cut 20'

Now, I wanted to eliminate interaction with images. So i tried using a
non-periodic box with the command 'boundary f f f' but it resulted in
zero neighbors and consequently (i think!) zero LJ energy. I was
expecting 2 neigbors for each atom since all fall within the LJ sigma
of 5. A periodic box gives 'Total # of neighbors = 18' in
the log file.

(units = real ; neighbor and neigh_modify are set to default)

Basically, I want to make sure that LJ interaction between the three
particles is direct i.e. just two terms per particle.

Any suggestions ? pointers to relevant bits of the code will also be helpful.


The neighbor count LAMMPS prints out includes interactions
with ghost atoms. If you don't want ghost atoms for
this problem than choose a cutoff shorter than the box length.
20 is extremely long for LJ.