• Welcome to ORCA

- New ORCA Release: ORCA 3.0.3 ! -
 ( See Release Notes of Version 3.0.3 ) 

- An ab initio, DFT and semiempirical SCF-MO package -
The program ORCA is a modern electronic structure program package written by F. Neese, with contributions from many current and former coworkers and several collaborating groups. The binaries of ORCA are available free of charge for academic users for a variety of platforms.
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.

What can ORCA do?
ORCA is able to carry out geometry optimizations and to predict a large number of spectroscopic parameters at different levels of theory. Besides the use of Hartee Fock theory, density functional theory (DFT) and semiempirical methods, high level ab initio quantum chemical methods, based on the configuration interaction and coupled cluster methods, are included into ORCA to an increasing degree.

Implemented Methods:
•Semiempirical INDO/S, MNDO, AM1, PM3, NDDO/1
•Hartee Fock theory (RHF, UHF, ROHF and CASSCF) all in direct, semidirect, or conventional mode, different RI approximations
•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 (with and without RI, Local)
•High level ab-initio individual selecting multireference methods (MRCI, MRMP2, MRMP3, MRMP4, MRACPF, MRAQCC, SORCI, DDCI) 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, picture change effects, all-electron basis sets, effective core potentials
•The COSMO model is available throughout the package for continuum dielectric modeling of the environment.
•QM/MM interface to GROMACS
•Double hybrid functionals including a fraction of nonlocal correlation. Analytic gradients are also available (these methods were invented by the Grimme group).
•Van der Waals correct density functionals.

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, Löwdin 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.
•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.

What are the special highlights of ORCA?
•User friendliness.
•Full Parallelization
•Interface to graphics programs.
•Some unique methods, in particular in the area of open-shells, spectroscopic parameters and MR-CI methods.

 New Features of Version 3.0: 
•Improved efficiency in integral evaluation and digestion, thanks to Ed Valeev for the improved libint 2.0 library!
•Improved parallelization, in particular for RI-DFT calculations.
•The DLPNO-CCSD(T) near linear scaling local correlation method. It has led to the first CCSD(T) level calculation on an entire protein.
•Explicitly correlated (F12) MP2 and coupled cluster methods using several approximations to boost the efficiency (They also work together with DKH/ZORA, COSMO etc.). Again many thanks for Ed Valeev for his countless contributions to this project.
•Efficient analytic frequencies for RI-DFT, hybrid DFT, Hartree-Fock and MP2 (also featuring QM/MM Hessians, ECPs, DKH/ZORA, van der Waals corrections etc., COSX and RI approximations).
•Interface to the large-scale DMRG program "BLOCK" developed by Garnet Chan and co-workers. it can be used together with the CASSCF module of ORCA.
•The "HF-3c" method by Grimme and co-workers is a slightly parametrized Hartree-Fock variant that can be applied to very large systems and can achieve stunning accuracy.
•Nonlocal van der Waals corrections have been implemented by the Grimme group
•A range of modern functionals, including M06-2X, have been implemented by the Grimme group making use of the XCFun DFT library by Ulf Ekstrom.
•Range corrected hybrid functionals have been implemented by the Grimme group
•Coupled cluster densities and new coupled cluster methods like orbital optimized and Brueckner coupled cluster methods.
•EOM-CCSD excitation energies for closed-shell systems.
•MP2 electric and magnetic response properties (but no NMR yet).
•A fully self consistent CASSCF method with spin-orbit coupling has been developed
•The ROCIS module features a new approach to the calculation of complicated X-ray absorption spectra that are dominated by spin-orbit and multiplet effects
•Natural transition orbital analysis for TD-DFT excited states.
•Effective Hamiltonian (infinite order) extraction of EPR parameters from QDPT calculations using MRCI and CASSCF/NEVPT2.
•The RIJCOSX-SCS-MP3 method.
•Removal of near linear dependencies in the orbital basis set.
•Improved overlap fitted COSX approximation.
•Geometric counterpoise correction.
•Finite nucleus for relativistic single point calculations.
•Finite temperature SCF calculations and correct gradients.
•Improved picture change theory for DKH magnetic property calculations.
•Extended correlation energy extrapolation schemes making use of of LPNO methods.
•Interface to NBO 6.0 and AIM.

 New Features of Version 3.0.1: 
This is mostly a bugfix release, a few new features made it into the release:
•EOM (parallel, InCore, OnDisk, improved convergence)
•SCFHESS (Intensities)
•NBO interface (NBO5 or NBO6 via environment variable)
•NumGeo (Keyword for numerical Hessian in OPT-runs using (Re)Calc_Hessian)
•Translation-invariance for numerical gradients
•TPrint now works with CIS

 New Features of Version 3.0.2: 
This is a mostly bugfix release, with a few new features:
•AMFI-A: AMFI (atomic mean field spin orbit coupling operator)-like approach with generated atomic densities
•otool_smd: newly implemented universal solvation model
•Extension of polarization-consistent basis sets (for K to Kr)
•Minimally augmented def2 basis sets

 New Features of Version 3.0.3: 
This is a strictly a bugfix release. Here is a detailed list of issues fixed.