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OS: Linux, ...

License: free for academic users, Registration

The program ORCA is a modern electronic structure program package

ORCA is a flexible, efficient and easy-to-use general purpose tool for quantum chemistry with specific emphasis on spectroscopic properties of open-shell molecules. It features a wide variety of standard quantum chemical methods ranging from semiempirical methods to DFT to single- and multireference correlated ab initio methods. It can also treat environmental and relativistic effects.

Due to the user-friendly style, ORCA is considered to be a helpful tool not only for computational chemists, but also for chemists, physicists and biologists that are interested in developing the full information content of their experimental data with help of calculations.

Implemented Methods:

Semiempirical AM1, PM3, ZINDO, NDDO, MNDO
Hartee Fock theory (RHF, UHF, ROHF and CASSCF)
DFT including a reasonably large number of exchange and correlation functionals including hybrid DFT and the most recent double hybrid functionals (see below).
High level single reference correlation models: CCSD(T), QCISD(T), CEPA, CPF (in version 2.6.0 for closed-shell ground states. Works with and without density fitting.
High level ab-initio individual selecting multireference methods (MRCI, MRMP2, MRMP3, MRMP4, MRACPF, MRAQCC, SORCI) for ground- and excited-states.
Geometry optimization in redundant internal coordinates using analytical gradient techniques for all SCF methods as well as MP2.
Excited state calculations via TD-DFT and CI-singles (CIS). For CIS an analytic gradient is also available. The doubles correction is available for CIS(D) in an efficient implementation.
Scalar relativistic ZORA, IORA and Douglas-Kroll-Hess (DKH) approaches.
The COSMO model is available throughout the package for continuum dielectric modelling of the environment.
Large number of user defined point charges can be read by the program which allows to interface existing QM/MM methods.

Special Methods

Double hybrid functionals including a fraction of nonlocal correlation. Analytic gradients are also available and these are presently exclusive to ORCA. (these methods were invented by the Grimme group)
Van der Waals correct density functionals. (Corrections are available for B3LYP, PBE, BLYP, TPSS and starting from version 2.5.30) also for the double hybrids B2PLYP and mPW2PLYP. The double hybrids and in particular the VDW corrected double hybrids have given the best energetic benchmarks ever observed for any density functional. (invented by the Grimme group)
Spin-component scaled MP2 (SCS-MP2). The individual scaling for the parallel and anti-parallel pair correlation energies provide a uniform improvement over standard MP2. Energies and gradients are available with and without the RI approximation. (invented by the Grimme group)
Individually selecting MR-CI program also featuring a number of coupled pair methods. A special technique is SORCI that gives good predictions for excitation energies at a fraction of the cost of full MR-CI. Also difference dedicated CI (DDCI) techniques are available in this program. Spin-Orbit interactions between the calculated roots of any multiplicity can be calculated.

Basis Sets:

a large number of built-in gaussian basis sets is available. User defined basis sets can be easily specified.

Population Analysis and related issues:

Mulliken, Loewdin and Mayer analyses
Convenient breakdown of MO populations and easy to set up fragment analysis
Orbital localization via the Pipek-Mezey algorithm.
Unrestricted natural orbitals and unrestricted corresponding orbitals.
Interface to the GENNBO program of Weinhold and co-workers.

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.
Moessbauer-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.