The Hartree-Fock exchange matrix is calculated through a procedure known as Resolution of the Identity (RI). The implementation of the RI scheme in BAND is loosely based on work by Ren et al. . For more information on hybrid functionals in BAND, see the XC section.
Technical aspects of the RI scheme can be tweaked in the
RIHartreeFock Quality [VeryBasic | Basic | Normal | Good | VeryGood | Excellent] FitSetQuality [VeryBasic | Basic | Normal | Good | VeryGood | Excellent] DependencyThreshold float AtomDepQuality # Non-standard block. See details. ... End End
Type: Block Description: The Hartree-Fock exchange matrix is calculated through a procedure known as Resolution of the Identity (RI). Here you can tweak various parameters of the procedure.
Type: Multiple Choice Default value: Normal Options: [VeryBasic, Basic, Normal, Good, VeryGood, Excellent] Description: Accuracy of numerical integration and thresholds of the RI procedure.
Type: Multiple Choice Default value: Normal Options: [VeryBasic, Basic, Normal, Good, VeryGood, Excellent] Description: The auxiliary fit set employed in the RI scheme. This is an important aspect of the procedure, significantly affecting both accuracy and computation time. For SZ and DZ basis set a ‘basic’ FitSetQuality will suffice. For ‘DZP’ and ‘TZP’ a normal quality is recommended. For larger basis set, use either ‘normal’ or better FitSetQuality.
Type: Float Default value: 0.001 Description: To improve numerical stability, almost linearly-dependent combination of basis functions are removed from the Hartree-Fock exchange matrix. If the SCF does not converge or you obtain unphysically large bond energy in an Hybrid calculation, you might try setting the DependencyThreshold to a larger value (e.g. 3.0E-3).
Type: Non-standard block Description: One can define a different fit-set quality for each atom. The syntax for this free block is ‘iAtom quality’, where iAtom is the index of the atom in input order.
For efficiency and numerical stability reasons, it is advisable to include:
SoftConfinement Quality Basic End
See the Confinement of basis functions section for more info.
Notes: for periodic systems it is only possible to use short-range hybrid functionals (e.g. HSE06) and all-electron basis sets.