non-numeric box dimensions-simulation unstable_ fix rigid/npt

Dear all,

I am trying to simulate semi crystalline polymer using lammps. I have few crystalline regions with polymer chains perfectly ordered and amorphous regions in which the polymer chains are randomly oriented.

I am using all atom simulation. I want all the crystalline regions to be rigid (it has 2000 atoms).
Let us say there are 5 crystalline regions and all 5 regions should behave individually rigid and move around.

Now I have to maintain the pressure in the entire system. I am trying to use rigid/npt single to crystalline and npt to amorphous region.

fix 10 crystal11 rigid/npt single temp 1 1 100 iso 10 10 10
fix 11 crystal12 rigid/npt single temp 1 1 100 iso 10 10 10
fix 12 crystal13 rigid/npt single temp 1 1 100 iso 10 10 10
fix 14 crystal14 rigid/npt single temp 1 1 100 iso 10 10 10
fix 17 crystal15 rigid/npt single temp 1 1 100 iso 10 10 10
fix 1 amorphous npt temp 1 1 100 iso 10 10 10

timestep 0.5

When I start the simulation, I get an error, non-numeric box dimensions-simulation unstable.

I understand there is difficulty in computing pressure for the entire system. Can anyone suggest some idea ?

Am I doing the right way to maintain the pressure?

Dear all,

I am trying to simulate semi crystalline polymer using lammps. I have few
crystalline regions with polymer chains perfectly ordered and amorphous
regions in which the polymer chains are randomly oriented.

I am using all atom simulation. I want all the crystalline regions to be
rigid (it has 2000 atoms).
Let us say there are 5 crystalline regions and all 5 regions should behave
individually rigid and move around.

Now I have to maintain the pressure in the entire system. I am trying to
use rigid/npt single to crystalline and npt to amorphous region.

fix 10 crystal11 rigid/npt single temp 1 1 100 iso 10 10 10
fix 11 crystal12 rigid/npt single temp 1 1 100 iso 10 10 10
fix 12 crystal13 rigid/npt single temp 1 1 100 iso 10 10 10
fix 14 crystal14 rigid/npt single temp 1 1 100 iso 10 10 10
fix 17 crystal15 rigid/npt single temp 1 1 100 iso 10 10 10
fix 1 amorphous npt temp 1 1 100 iso 10 10 10

timestep 0.5

When I start the simulation, I get an error, non-numeric box
dimensions-simulation unstable.

I understand there is difficulty in computing pressure for the entire
system. Can anyone suggest some idea ?

Am I doing the right way to maintain the pressure?

‚Äčno. pressure is a global property and thus you can have only one fix that
modifies‚Äč the cell volume. you have several and they each corrupt the time
integration for the box size adjustments of each other. this and strategies
to deal with it are explained in the fix rigid documentation. it has many
"important note" sections; you should study them well.

totally unrelated, but since you already have groups, you will be better
off using a single fix rigid/nvt with the group option to define individual
rigid bodies. each fix rigid with single will require broadcast and
reduction operations to update the rigid body data, so you will negatively
affect performance with your setup.

axel.