More Technical Settings¶

There are of course many other settings influencing the precision and performance. Usually the user does not need to care about them.

Linear Scaling¶

Tails
Bas float
End

Tails
Type: Block Ignore function tails.
Bas
Type: Float 1e-06 Cut off the basis functions when smaller than the specified threshold.

Dependency¶

Dependency
Basis float
Core float
CoreValence float
Fit float
End

Dependency
Type: Block Criteria for linear dependency of the basis and fit set
Basis
Type: Float 1e-08 Criteria for linear dependency of the basis: smallest eigenvalue of the overlap matrix of normalized Bloch functions.
Core
Type: Float 0.98 The program verifies that the frozen core approximation is reasonable, by checking the smallest value of the overlap matrix of the core (Bloch) orbitals against this criterion.
CoreValence
Type: Float 1e-05 Criterion for dependency of the core functions on the valence basis. The maximum overlap between any two normalized functions in the two respective function spaces should not exceed 1.0-corevalence
Fit
Type: Float 5e-06 Criterion for dependency of the total set of fit functions. The value monitored is the smallest eigenvalue of the overlap matrix of normalized Bloch sums of symmetrized fit functions.

Screening¶

Band performs many lattice summations which are in practice truncated. The two prime examples are the construction of the Bloch basis and the calculation of the solvation potential. The precision of the lattice summations is controlled by the Screening key

Screening
CutOff float
DMadel float
NoDirectionalScreening [True | False]
RCelx float
RMadel float
End

Screening
Type: Block For the periodic solvation potential and for the old (not default anymore) fitting method, BAND performs lattice summations which are in practice truncated. The precision of the lattice summations is controlled by the options in this block.
CutOff
Type: Float Criterion for negligibility of tails in the construction of Bloch sums. Default depends on Accuracy.
DMadel
Type: Float One of the parameters that define the screening of Coulomb-potentials in lattice sums. Depends by default on Accuracy, rmadel, and rcelx. One should consult the literature for more information
NoDirectionalScreening
Type: Bool Real space lattice sums of slowly (or non-) convergent terms, such as the Coulomb potential, are computed by a screening technique. In previous releases, the screening was applied to all (long-range) Coulomb expressions. Screening is only applied in the periodicity directions. This key restores the original situation: screening in all directions
RCelx
Type: Float Max. distance of lattice site from which tails of atomic functions will be taken into account for the Bloch sums. Default depends on Accuracy.
RMadel
Type: Float One of the parameters that define screening of the Coulomb potentials in lattice summations. Depends by default on Accuracy, dmadel, rcelx. One should consult the literature for more information.

Direct (on the fly) calculation of basis and fit¶

BAND usually calculates basis functions and theirs derivatives on the fly. However, for small bulk systems it can be faster to write the information to disk. Then one can set the DirectBas key to false. (Default = true)

Programmer
DirectBas bool
End


Block size¶

CPVector integer

CPVector
Type: Integer 128 The code is vectorized and this key can be used to set the vector length
KGrpX integer

KGrpX
Type: Integer 5 Absolute upper bound on the number of k-points processed together. This only affects the computational performance.