8.3. The Scaling section

The $scaling section supports finite-size scaling through different supercell sizes.

8.3.1. Finite-size scaling

Finite size scaling is supported with a special “scaling” subsection.

Defect positions will be automatically scaled.

  • For example, 0.25 0.0 0.0 in the original supercell would become 0.125 0.0 0.0 in a 2x1x1 cell.

Special notes:

  • The Ingredients section should include an “inducescaling” ingredient with a mast_run_method of run_scale

  • The Recipe section should include inducescaling_<S> and defect_<S> ingredients.

    • The “<S>” tags will correspond to the scaling sizes and labels.

For each scaling size, create a subsection with begin <labelname>.

Within the subsection, include keywords:

  • mast_size with a scaling matrix of integers [M, N, P] or [M1 M2 M3, N1 N2 N3, P1 P2 P3]
  • mast_kpoints with a Kpoint mesh in the form QxRxS, followed by a
  • Kpoint mesh type, M for Monkhorst-Pack and G for Gamma-point centered
  • (Optional) Kpoint mesh shift, in floats, e.g. 0.1 0.2 0.3
  • WILL OTHER KEYWORDS NOW WORK AS WELL, FOR OVERRIDING?

Example:

$scaling
begin 2xhigh
mast_size [2, 2, 2]
mast_kpoints 4x4x4 M
end
begin 4xhigh
mast_size [4, 4, 4]
mast_kpoints 2x2x2 M
end
$end

NEED TO VERIFY MADELUNG POTENTIAL CHANGES

In order to figure out which scaling sizes to use for finite-size scaling, MAST includes a Madelung potential utility.

This utility generates a distribution of cell sizes for best scaling, according to the method in:

Hine, N. D. M., Frensch, K., Foulkes, W. M. C. & Finnis, M. W. Supercell size scaling of density functional theory formation energies of charged defects. Physical Review B 79, 13, doi:10.1103/PhysRevB.79.024112 (2009).

Run this utility as follows in order to generate a cut-and-paste for the scaling section.

mast_finite_size_scaling_sizes perfDir defDir minDefDist maxNumAtoms numStructAsked
  • perfDir: perfect primordial (small) cell directory, which should already have run and include VASP CONTCAR, OSZICAR, etc. files.
  • defDir: defected primordial cell directory, which should already have run and include VASP CONTCAR, OSZICAR, etc. files.
  • minDefDist (default 3): minimum defect-defect distance between periodic images, in Angstroms.
  • maxNumAtoms (default 600): maximum number of atoms for supercell size evaluations
  • numStructAsked (default 5): number of structures to return in the distribution
  • Note that you will have to manually adjust the kpoint mesh in your cut-and-paste.