Orca is a general purpose quantum chemistry program with emphasis in spectroscopy. It's free for academic use.

Written by Franck Neese

Methods included in version 2.6.35:

  • Semiempirical AM1, PM3, ZINDO, NDDO, MNDO
  • Hartree Fock theory (RHF, UHF, ROHF, CASSCF, SCS-MP2)
  • DFT including double hybrid functionals
  • Single reference: CCSD(T), QCISD(T), CEPA, CPF
  • Multi-reference: MRCI, MRMP2, MRMP3, MRMP4, MRACPF, MRAQCC, SORCI
  • Geometry optimization
  • Excited state calculations via TD-DFT and CI-singles (CIS).
  • Scalar relativistic ZORA, IORA and Douglas-Kroll-Hess (DKH)
  • COSMO model for solvent
  • Allows interface with existing QM/MM methods.

Spectroscopic Parameters:

  • Absorption and CD spectra from time-dependent DFT or MR-CI.
  • EPR-parameters: Zero-Field Splittings, g-tensors, hyperfine couplings, quadrupole tensors from Hartree-Fock, DFT and MR-CI. Scalar relativistic corrections at the ZORA level.
  • Mössbauer-parameters: isomer-shift and quadrupole splitting.
  • Exchange coupling constants from broken-symmetry DFT (and pathway analysis) or Difference-dedicated CI (DDCI).
  • NMR-parameters: chemical shifts from HF or DFT (but not with GIAO’s; IGLO is available)
  • IR / RAMAN spectra, isotope shifts via numerical frequency calculations (HF and DFT)
  • Simulation of absorption bandshapes and resonance-Raman excitation profiles from TD-DFT or MR-CI calculations

More information: