Hartree–Fock RI scheme¶
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 key block:
RIHartreeFock Quality [basic|normal|good|verygood] FitSetType [Mirko|ET6|ET7|ET8] DependencyThreshold 1.0E-3 End
- (Default: Normal) Set the numerical quality of some internal technical procedures, including numerical integration and linear scaling parameters.
- (Default: Mirko) The auxiliary fit set employed in the RI scheme. ET8 is a fairly large fit set, and can be used for assessing the accuracy of the RI procedure.
- (Default: 1.0E-3) To improve numerical stability, almost linearly-dependent combination of basis functions are removed from the Hartree-Fock exchange matrix. If you obtain unphysical large bond energy in an Hybrid calculation, you might try setting the
DependencyThresholdto a larger value (e.g. 3.0E-3).
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) in combination with all-electron basis sets.