GEDIIS Geometry-Space DIIS

GEDIIS extrapolates from previous geometry/gradient points to accelerate optimisation. Enable with Diis true.

Basic GEDIIS Usage

task: OPT RHF STO-3G

GEOMETRY
  O   0.000000   0.000000   0.100000
  H   0.750000   0.000000  -0.450000
  H  -0.750000   0.000000  -0.450000
END

OPT
  Diis     true
  DiisSize 4
END

Combined with Berny RFO and Larger DIIS Subspace

OPT
  Algorithm  berny
  Diis       true
  DiisSize   6
  MaxCycle   200
END

TS Search with GEDIIS (Berny)

task: TS RHF STO-3G

GEOMETRY
  ...
END

OPT
  TransitionState true
  Diis            true
END

Sella with GEDIIS

Sella minimum search:

task: SELLA RHF STO-3G

GEOMETRY
  ...
END

OPT
  Algorithm sella
  Diis      true
END

Sella TS with GEDIIS:

task: TS SELLA RHF STO-3G

GEOMETRY
  ...
END

OPT
  Algorithm       sella
  TransitionState true
  Diis            true
END

Sella TS + GEDIIS + Bofill:

task: TS SELLA RHF STO-3G

GEOMETRY
  ...
END

OPT
  Algorithm       sella
  TransitionState true
  Diis            true
  Update          bofill
END

Rust Berny with GEDIIS

OPT
  Algorithm  rberny
  Diis       true
END

Notes

• GEDIIS is most effective for:
  • Difficult optimizations near flat PES regions
  • Multi-step convergences where optimizer oscillates
  • Large molecules where SCF is expensive
• Typically reduces optimization cycles by 20–40% for well-behaved systems
• When DIIS is enabled in supported optimizers, you usually run a GEDIIS pipeline that can fall back to GDIIS internally (RFO-DIIS → EnDIS → GDIIS)
• For debugging DIIS behavior, set OPENQ_DIIS_TRACE=1