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 QualityPerRegion Quality [VeryBasic | Basic | Normal | Good | VeryGood | Excellent] Region string 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] GUI name: RI Hartree-Fock 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: Block Recurring: True Description: Sets the fit-set quality for all atoms in a region. If specified, this overwrites the globally set quality.
Type: Multiple Choice Options: [VeryBasic, Basic, Normal, Good, VeryGood, Excellent] Description: This region’s quality of the auxiliary fit set employed in the RI scheme.
Type: String Description: The identifier of the region for which to set the quality.
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.
- In AMS2019.3 the fit set for
FitSetQuality Goodhas been improved.
|||X. Ren, P. Rinke, V. Blum, J. Wieferink, A. Tkatchenko, A. Sanfilippo, K. Reuter and M. Scheffler, Resolution-of-identity approach to Hartree–Fock, hybrid density functionals, RPA, MP2 and GW with numeric atom-centered orbital basis functions, New J. Phys. 14 053020.|