Glass Materials

This section provides a few example of control parameters and simulation procedures for a number of system materials. It can be used as a guidance for your system model.

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Example 1: Rare-earth (La, Y, Lu, Sc) aluminosilicate

Reference: K. Okhotnikov, B. Stevensson and M. Edén, Phys. Chem. Chem. Phys. 15, 15041 (2013)

Model size: 35Å x 35Å x 35Å, ~3300 atoms.

Procedures: Run at a high temperature to melt the system. Then, quenched (lower) it to a desired temperature:

  1. Melt to equilibrate the structure at 3500 K for 100 ps
  2. Stepwise decrease temperature every 10 ps at a rate of 10 K ps -1 to 300 K
  3. Run for 200 ps at 300 K and simulation extracted for analysis for the last 150 ps.

Repeat the procedures 12 times, each starts with a different initial configurations to obtain average results.

DL_FIELD FF scheme: inorganic_glass.

Example 1 DL_POLY CONTROL file:

integrator velocity
ensemble nvt berendsen 1.0 
temperature 300 kelvin
timestep 0.002 pico-seconds
steps 10000 steps (arbitrary)
trajectory 0 20 0 (arbitrary, write out every 20 steps)
# restart

rcut     12.0 Angstrom
rvdw     8.0 Angstrom
ewald precision 1.0e-6

finish

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Example 2: Silicate glasses

Reference: A. Tilocca, N.H. de Leeuw, and A.N. Cormack, Phys. Rev. B 73, 104209 (2006)

Model: Use of core-shell model (adiabatic) with small mass assigned to shell parts. Use smaller timestep than usual, to correctly keep track of the shell with a much faster motion due to small mass.

Protocols: Run at a high temperature to melt the system, and then quenched (lower) it to a desired temperature. Investigate ion migration in glass structure.

Example 2 DL_POLY CONTROL file:

integrator velocity
ensemble nvt berendsen 1.0 (value not disclosed)
temperature 300 kelvin
timestep 0.0002 pico-seconds (0.2 fs)
steps 10000 steps (arbitrary)
# restart

rcut     12.0 Angstrom
rvdw     8.0 Angstrom
ewald precision 1.0e-6 (value not disclosed)
finish

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Example 3: Oxide glasses

Reference: B.W.M. Thomas, R.N. Mead and G. Mountjoy, J. Phys.: Condens. Matter 18 4697 (2006)

Model: 23.7Å x 23.7Å x 23.7Å, 1000 atoms.

Protocols: Run at a high temperature to melt the system, and then quenched (lower) it to a desired temperature. Investigate ion migration in glass structure.

  1. At 6000K for 40,000 MD steps.
  2. Change to 4000 K for 40,000 MD steps.
  3. Change to 2000 K for 40,000 MD steps.
  4. Quench from 2000 K to 300 K over 85,000 steps. (10 13 K s -1)
  5. Sample structure at 300 K for 40,000 steps (without further equilibration), sampled every 200 steps.

Use Berendsen temperature bath to maintain temperature at NVT for all stages.

Example 3 DL_POLY CONTROL file:

integrator velocity
ensemble nvt berendsen 2.0 
temperature 300 kelvin
timestep 0.002 pico-seconds (2 fs)
steps 10000 steps (arbitrary)
trajectory 0 200 0 (write out every 200 steps)
# restart

rcut     10.0 Angstrom (assume)
rvdw     10.0 Angstrom
ewald precision 1.0e-5

finish

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Example 4 Silica Yttrium Aluminosilicate glass

Reference: J. Du, J. Am. Ceram. Soc. 92, 87 (2009)

System size: about 2900 atoms

Protocols: Run at a high temperature to melt the system, and then quenched (lower) it to a desired temperature.

  1. Run NVT ensemble at 6000 K to randomise the structure for 80 ps.
  2. Run NVE ensemble at 6000 K for a further 80 ps.
  3. Temperature is changed (lowered) to 4000 K and run for 80 ps at NVT.
  4. Run NVE ensemble at 4000 K for a further 80 ps.
  5. Temperature linearly scaled down to 300 K at the rate 10 K/ps.
  6. Run NVT at 300 K for 80 ps.
  7. Run NVE at 300 K for a further 80 ps. Collect data for analysis for the final 40 ps.

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