Standard Optimization

Geometry optimization finds a local minimum on the potential energy surface by iteratively updating nuclear positions. The default optimizer uses Cartesian coordinates with a BFGS Hessian update.

Geometry Optimization — Water, RHF/6-31G*

task: OPT RHF 6-31G*

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

Geometry Optimization — Methyl Radical (UHF Doublet)

task: OPT UHF 6-31G*

MOLECULE
  Multiplicity  2
END

GEOMETRY
  C   0.000000   0.000000   0.000000
  H   0.000000   1.079000   0.000000
  H  -0.934000  -0.539500   0.000000
  H   0.934000  -0.539500   0.000000
END

Notes

  • For UHF optimization, set Multiplicity 2 in MOLECULE.
  • The default optimizer is Berny RFO with Cartesian coordinates.
  • Each cycle warm-starts the SCF from the previous cycle's converged orbitals, which usually cuts SCF iterations substantially after the first step. Disable with MOGuess false in the OPT section.
  • See Internal Coordinates, Berny/Rust Berny, and GEDIIS for advanced options.