SCF Convergence & DIIS

SCF with Tight Convergence and Custom DIIS

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

SCF
  MaxCycle 200
  Conver   10
  Diis     10
END

DIIS Parameters

KeywordDefaultDescription
MaxCycle100Maximum SCF iterations
Conver8Convergence threshold = 10⁻ᴺ
Diis6DIIS subspace size
NoDiisfalseDisable DIIS

Tight Convergence Preset

SCF
  Tight true
END

This sets Conver 10 and tighter thresholds automatically.

Disable DIIS

SCF
  NoDiis true
END

Useful for systems where DIIS oscillates.

Level Shift

SCF
  Shift 0.5
END

Static level shift in Hartree. Helps with difficult convergence (e.g., open-shell transition metals).

Dynamic Level Shift

SCF
  VShift true
END

Dynamic virtual orbital level shift (automatically adjusts).

Fermi Broadening

SCF
  Fermi 0.01
END

Fermi-Dirac broadening for metallic/near-degenerate systems. Helps with convergence by smearing the Fermi surface.