ERI Engine Selection

Choose the ERI engine for the whole calculation (energy, gradient, Hessian, and SCF paths):

INT
  Eri  auto
END

Engine Options

Eri=Description
autoFast SP + Rys routing (S/P→SP, higher-L→Rys, MD fallback) — recommended
mdMcMurchie–Davidson (default, most general)
sp / spfastSP fast paths for S/P shells, MD fallback for higher-L
rys / rysquadratureRys-first with MD fallback

SP Analytical Fast Paths — H₂O, STO-3G

task: RHF STO-3G

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

INT
  Eri spfast
END

Rys Quadrature — H₂O, cc-pVDZ (D functions)

task: RHF CC-PVDZ

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

INT
  Eri rys
END

Fast SP + Rys Auto Engine (Recommended)

task: RHF DEF2-TZVP

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

INT
  Eri auto
END

Pure MD Engine (Baseline)

task: RHF DEF2-TZVP

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

INT
  Eri md
END

Notes

  • The selected ERI engine applies to all ERI computation paths: in-core integral build, direct SCF, analytical gradients, fully analytical Hessians, and semi-analytical (FD) Hessians.
  • Eri auto is recommended for general use — it routes S/P shells through fast paths and higher angular momentum through Rys quadrature with MD fallback.