I am trying to simulate polymer systems using OPLS force field.
The system consists of Polyethylene chains and peroxide molecules on top of them.
I build the structure PE and peroxide parts separately and merge them using read data command twice.
Everything works fine. I minimize the structure without any problem. The system is a slab, periodic in x-y directions only. I defined a LJ wall at top and bottom of the structure using :
fix bottomwall all wall/lj93 zlo 5.0 2 2 5
variable linear equal ramp(170,105.0)
fix topwall all wall/lj93 zhi v_linear 2 2 5
The top wall moves down to 105A in 100000 steps to compress the system in order to set the correct density.To avoid close contacts I built the structure with low density at the beginning.
Still no problem here. Bottomwall is fixed.
I start data collection part, nvt simulation at 500K for 2000000 steps.
After 243398 steps I received this error:
ERROR on proc 2: Dihedral atoms 17112 17117 17118 17032 missing on proc 2 at step 243398 (../ntopo_dihedral_al
I searched this error, it says usually bad construction of structure like close contacts of atoms etc. However I do not think thats the case here because the simulation runs more than 300 000 steps before getting this error and also minimizes without any problem. Here is my neighbor settings:
neighbor 7.0 bin
neigh_modify every 2 delay 2 check yes
I increased the skin size to see it helps but no luck. Increased the neighborlist build frequency but still error persists.
Finally my force field parameters:
pair_style lj/cut/coul/cut 10.0 8.0
pair_modify mix geometric tail yes
special_bonds lj/coul 0.0 0.0 0.5
#force field parameters