The crystalline structure of my silicon supercell becomes amorphous when I use NVT

Hello all,

I am performing a heating-quenching method to stabilize the temperature of my silicon supercell. I increase the temperature from 1K to 400K and then cool it down from 400K to 100K, which is my target final temperature. I conduct the heating and cooling in steps of approximately 30K using NVT. Between each step, I also use NVT at the same temperature to stabilize the system before proceeding to the next step. The problem is that after about 100ps the silicon becomes amorphous instead of maintaining its diamond structure.

I have also tried using NPT for this method, but I encounter the same issue. My goal is to ensure that the final velocities of the silicon atoms are representative of their actual movement, which is why I am employing this heating-quenching approach.

How can I achieve this objective without losing the crystallinity of silicon?

More details:

  • I am using the Tersoff potential.
  • The size of my system is 8x8x12 elementary cells of silicon (8 atoms per elementary cell). So 6144 atoms in total
  • I heat the system over 300 ps and cool it over 600 ps.
  • The timestep (dt) is 1 fs.
  • The temperature damping parameter (Tdamp) is 100*dt.
  • The first and last layers are composed of silicon atoms at 0K to ensure structural stability.
  • The second and second-to-last layers are maintained at 100K throughout the simulation using NVT. Used here to dissipate excess thermal energy

Please note that I don’t believe the problem arises from the frozen layers or the 100K layers; I encounter exactly the same issues even without them.

Solved : I only had to change the potential

The amorphization disappear using SW potential