DFTB

References: Porezag1995, Seifert1996, Elstner1998, Zhechkov2005

Parameters needed to set up the DFTB methods [Edit on GitHub]

Subsections

Keywords

Keyword descriptions

DIAGONAL_DFTB3

Type: logical
Default: F
Lone keyword: T
Usage: DIAGONAL_DFTB3

Description: Use a diagonal version of the 3rd order energy correction (DFTB3)

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DISPERSION

Type: logical
Default: F
Lone keyword: T
Usage: DISPERSION

Description: Use dispersion correction

References: Zhechkov2005

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DO_EWALD

Type: logical
Default: F
Lone keyword: T
Usage: DO_EWALD

Description: Deprecated debug override for the DFTB Ewald treatment. By default the setting is inferred from SUBSYS/CELL/PERIODIC. If set to TRUE, the DFT/POISSON section must use a periodic Poisson solver.

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Warning

The keyword DO_EWALD is deprecated and may be removed in a future version.

Use SUBSYS/CELL/PERIODIC to select periodicity. DO_EWALD is retained only as a debug override for the DFTB Ewald path.

EPS_DISP

Type: real
Default: 1.00000000E-004
Usage: EPS_DISP

Description: Define accuracy of dispersion interaction

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HB_SR_GAMMA

Type: logical
Default: F
Lone keyword: T
Usage: HB_SR_GAMMA

Description: Uses a modified version for the GAMMA within the SCC-DFTB scheme, specifically tuned for hydrogen bonds.

References: Hu2007

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ORTHOGONAL_BASIS

Type: logical
Default: F
Usage: ORTHOGONAL_BASIS

Description: Assume orthogonal basis set

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SCC_MIXER

Type: enum
Default: AUTO
Usage: SCC_MIXER (AUTO|TBLITE|CP2K|NONE)

Description: Selects the SCC variable mixer for CP2K-internal DFTB calculations. AUTO keeps the existing CP2K density/SCF mixing path for DFTB. The SCC variables are the model populations and, where required by the selected method, atomic multipoles that feed the self-consistent xTB potential. TBLITE uses tblite’s modified Broyden mixer for those variables inside the CP2K SCF cycle. CP2K maps the variables onto CP2K’s charge-mixing infrastructure. When TBLITE is active, the native SCC convergence follows XTB/TBLITE/ACCURACY and the tblite-side SCC update limit follows TBLITE_MIXER/ITERATIONS. If SCC_MIXER is explicitly set to TBLITE, CP2K also sets DFT/SCF/MAX_SCF to TBLITE_MIXER/ITERATIONS. With SCC_MIXER AUTO or CP2K, MAX_SCF keeps its normal CP2K meaning. With QS/LS_SCF, explicit SCC_MIXER settings are reset to NONE internally and CP2K emits a warning; LS_SCF controls the density-matrix optimization. When CP2K is active, convergence follows the normal CP2K SCF controls, in particular DFT/SCF/EPS_SCF and DFT/SCF/MIXING. For GFN2/tblite, the CP2K mixer acts on the full SCC-variable set: shell charges plus atomic dipole and quadrupole variables. CP2K-internal GFN0-xTB has no SCC variables to mix, so AUTO and NONE are equivalent there and explicit CP2K or TBLITE mixer choices are reset to NONE. For CP2K-internal GFN1 and DFTB/DFTB3, the SCC variables are only charge or shell-charge like. The initial SCC variables are seeded from CP2K’s current density, so DFT/SCF/SCF_GUESS and DFT/WFN_RESTART_FILE_NAME define the starting point. NONE performs direct updates without mixing and is intended for debugging, since it can be unstable.

Valid values:

  • AUTO Default method-dependent choice.

  • TBLITE Use the tblite modified Broyden SCC mixer.

  • CP2K Use CP2K charge mixing for SCC variables.

  • NONE Do not mix SCC variables; for debugging.

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SELF_CONSISTENT

Type: logical
Default: T
Usage: SELF_CONSISTENT

Description: Use self-consistent method

References: Elstner1998

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