Union two regions problem


I would like to construct two boxes connected by a cylinder.

First I defined two regions as block and one region as cylinder, as follow:
region 1 block -14 14 -14 14 0.0 14 side in units box
region 2 cylinder z 0.0 0.0 10.0 -10.0 0.0 side in units box
region 3 block -14 14 -14 14 -28.0 -10.0 side in units box

Next I join this three regions through the union commad:
region 4 union 3 1 2 3 side in units box

And finally, I give an atribute to the walls of this region:
fix wall all wall/region 4 lj126 1.0 1.0 2.5

The atoms are initially inside one of the boxes. I am using the CHARMM
potential and the only interaction between the atoms are van der Waals.

When I run this simulation I receive the following error message:
“Particle on or inside surface of region used in fix wall/region”

I do not know if I am doing some mistake in my input. Anyone could help


Gustavo Brunetto

Applied Physics Department
Institute of Physics Gleb Wataghin - IFGW
State University of Campinas - UNICAMP
Campinas - SP - Brazil - CEP 13083-970
Caixa Postal 6165
Room 61
Fone +55 19 3521-5373
Fax +55 19 3521-5343
e-mails: gusbru@…527… / gustavobruneto@…24…

If you get this error immediately, then see the
2nd IMPORTANT NOTE on the fix wall/region doc
page. If you get this error after running a while
then it might be the 1st IMPORTANT NOTE
on that doc page. I assume you have read that
doc page carefully, and understand whether what
you are trying to do makes sense.