SCF input documentation

Initialize parameters of self-consistent field iteration (SCF).

Used to initialize class qimpy.electrons.SCF.

YAML template:

n-iterations: 50           # Number of self-consistent field iterations / cycles.
energy-threshold: 1e-08    # Energy convergence threshold in Hartrees.
residual-threshold: 1e-07  # Residual-norm convergence threshold.
n-consecutive: 2           # Number of consecutive iterations each threshold must be satisfied.
n-history: 10              # History size for Pulay mixing.
mix-fraction: 0.5          # Fraction of new variable mixed into current variable.
mix-fraction-mag: 1.5      # Different mix_fraction for magnetization components.
q-kerker: 0.8              # Characteristic wavevector for Kerker mixing.
q-metric: 0.8              # Characteristic wavevector controlling Pulay metric.
q-kappa: null              # Long-range cutoff wavevector for grand-canonical SCF.
n-eig-steps: 2             # Number of inner eigenvalue iterations for each SCF cycle.
eig-threshold: 1e-08       # Convergence threshold on eigenvalues in Hartrees.
mix-density: yes           # Whether to mix density or potential.

Parameters:

n-iterations

Type: int, Default: 50

Number of self-consistent field iterations / cycles.

energy-threshold

Type: float, Default: 1e-08

Energy convergence threshold in Hartrees. Stop when energy difference between consecutive iterations falls below this threshold.

residual-threshold

Type: float, Default: 1e-07

Residual-norm convergence threshold. Stop when the norm of the residual i.e. difference in mixed variable (density / potential) between consecutive iterations falls below this threshold.

n-consecutive

Type: int, Default: 2

Number of consecutive iterations each threshold must be satisfied.

n-history

Type: int, Default: 10

History size for Pulay mixing. This sets the number of previous residuals and variables to use in the Pulay mixing algorithm. Larger history could improve convergence, while requiring more memory.

mix-fraction

Type: float, Default: 0.5

Fraction of new variable mixed into current variable. Lower values (< 0.5) can improve stability, while higher values (0.5 - 1) attempt more aggressive convergence.

mix-fraction-mag

Type: float, Default: 1.5

Different mix_fraction for magnetization components. More aggressive fractions (> 1) are typically required to converge the magnetization degrees of freedom, because they tend to contribute less to the overall energy of the system (compared to the overall electron density / potential).

q-kerker

Type: float, Default: 0.8

Characteristic wavevector for Kerker mixing.

q-metric

Type: float, Default: 0.8

Characteristic wavevector controlling Pulay metric.

q-kappa

Type: float or null, Default: null

Long-range cutoff wavevector for grand-canonical SCF. If unspecified, set based on Debye screening length.

n-eig-steps

Type: int, Default: 2

Number of inner eigenvalue iterations for each SCF cycle.

eig-threshold

Type: float, Default: 1e-08

Convergence threshold on eigenvalues in Hartrees. Stop when the maximum change in any eigenvalue between SCF cycles falls below this threshold.

mix-density

Type: bool, Default: yes

Whether to mix density or potential. Mix density if yes, and potential if no.