Step 5 - Equilibrate the Box
To ensure that our silicon and oxygen atoms are well mixed and distributed we’re going to “cook” the box at a high temperature to start with.
Go to the
Bulk configuration tab
On the configuration viewer toolbar, click the button
Change the Temperature to 2000.0
Now we’ll run for 250 steps:
Simulation ⇨ Run For…
Set the number of steps to 250 and click
You can open the
NeutronSQ module in the RDF / Neutron S(Q) layer to monitor the structure, or the
Energy module in the Evolve (Basic Atomic) to check the energy as the simulation progresses. The total energy will be large and negative - of the order of –4×106. When finished, the F(Q) and G(r) should look a little like this:
Calculated structure factor (black line) of amorphous silica at high temperature (2000 K) compared to reference data at 298 K (red line)
Calculated total G(r) (black line) of amorphous silica at high temperature (2000 K) compared to Fourier transform of reference data at 298 K (red line)
We’ll now reset the temperature of the box to 298 K and run a second equilibration.
Go to the
On the configuration viewer toolbar, click the button
Change the Temperature to 298.0
Simulation ⇨ Run For…
Set the number of steps to 250 and click
Once finished, the structure should look a lot better:
Equilibrated structure factor (black line) of amorphous silica compared to reference data at 298 K (red line)
Equilibrated total G(r) (black line) of amorphous silica compared to Fourier transform of reference data at 298 K (red line)