INT Section

The INT section controls integral computation: ERI screening, engine selection, symmetry, and grid settings.

Keywords

KeywordTypeDefaultDescription
Acc2Einteger12ERI screening threshold = 10⁻ᴺ
UltraFinebooleanfalseUse larger integration grid
Eriauto | md | sp | rysautoERI engine selection
NoSymmbooleanfalseDisable point-group symmetry
GridCoarse | Fine | UltraFineFineDFT integration grid (future)
Relativisticdk | zora | nonenoneRelativistic Hamiltonian (future)
FcModinteger0Freeze-core shell count (per atom)
Semiempiricalstring—Activate a semiempirical method

ERI Engine Selection

EngineEri valueBest forNotes
McMurchie–DavidsonmdAll systems (default)Universal, correct for all angular momenta
SP Fast Pathssp / spfastOrganic (H,C,N,O,F)10× ERI speedup for S/P shells only
Rys Quadraturerys / rysquadratureTransition metals, D/F+Rys-first with MD fallback
AutoautoGeneral useFast SP + Rys routing, MD fallback

The selected engine applies to all ERI computation paths: in-core integral build, direct SCF, analytical nuclear gradients, fully analytical Hessians, and semi-analytical (FD) Hessians.

Examples

Recommended (auto):

INT
  Eri  auto
END

Force McMurchie–Davidson (baseline):

INT
  Eri  md
END

SP fast paths for organic molecules:

INT
  Eri  sp
END

Rys quadrature for transition metals:

INT
  Eri  rys
END

Disable symmetry:

INT
  NoSymm true
END

Tighter ERI screening:

INT
  Acc2E 14
END

DFT integration grid (future):

INT
  Grid UltraFine
END

Notes

  • Acc2E 12 (10⁻¹²) is the default ERI screening threshold.
  • Symmetry is enabled by default. NoSymm true skips point-group ERI screening and prints all orbital irreps as A (C1 symmetry).
  • The 8-fold permutational symmetry of ERIs is always applied regardless of NoSymm.
  • The Grid keyword controls the DFT numerical integration grid (for future DFT support).