Hello,

I am trying to run an NPT simulation where the temperature is controlled using the Andersen thermostat algorithm and the pressure is controlled using the Parrinello barostat algorithm on a nylon66 crystal structure provided by materials studio (Structures\\polymers\\crystalline\\nylon-6-6-alpha.xsd).

When I import the file I first hydrate it since it appears to be missing some hydrogens. After that I make a supercell and apply the COMPASS force field to the crystal prior to submitting it to discover on the supercomputer.

The relevant portion of the script is below:

   dynamics \\
    time = 100000.00 \\
    boltzmann \\
    timestep = 1.00 \\
    initial_temperature = 300.00 \\
    ensemble = NPT \\
    temperature_control_method = andersen \\
    collision_ratio = 1.00 \\
    temperature = 300.00 \\
    press_choice = stress \\
    stress = {0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 } \\
    pressure_control_method = parrinello \\
    cell_mass = 20.0 \\
    deviation = 50000.00 \\

I get the error "Error: Dynamics: Energy difference between successive steps in dynamics is greater than the user defined variable DEVIATION, 50000.00"

I looked at decreasing the timestep of 0.10 and increased deviation to 100000000.00, and I get the same error.

When I looked at a different supercell, I could get it to run but the volume gets really big, such that the density is pretty much zero. Not sure what is wrong. I did this for other crystal structures and did not have this problem.

Thanks,

Tanya