• Welcome to ORCA

- New ORCA Release: ORCA 4.0.1 ! -
 ( See Release Notes of Version 4.0.1 ) 

- 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 4.0.1: 
ORCA 4.0.1 is strictly a bugfix release. For a detailed list changes
please consult the ORCA 4.0.1 Release Notes

 New Features of Version 4.0.0: 

New Methods:
•Linear scaling DLPNO-CCSD(T) open shell. New restricted open-shell formulation
•Linear scaling DLPNO-MP2 (RHF and UHF)
•Linear scaling DLPNO-MP2-F12 (RHF)
•Linear scaling DLPNO-CCSD(T) (the 2013 implementation is still available)
•Linear scaling DLPNO-CCSD(T) local energy decomposition scheme
•Linear scaling DLPNO-CCSD closed shell density
•Linear scaling cluster in molecule (CIM): MP2, CCSD(T), DLPNO-CCSD(T)
•Linear scaling DLPNO-NEVPT2
•Updated interface to BLOCK 1.0
•Closed shell EOM-CCSD energies
•Closed shell STEOM-CCSD energies
•Partial PNO-EOM-CCSD method for excited states
•Partial PNO-STEOM-CCSD method for excited states
•Mukherjee Mk-LPNO-MRCCSD(T)
•Powerful iterative configuration expansion (ICE-CI) approximation to Full-CI
•ICE-CI for large active space CASSCF calculations
•MREOM-CCSD (also with SOC)
•Fully internally contracted MRCI
•Full TD-DFT energies and gradient for hybrid functionals
•Super-fast approximate TD-DFT: sTDA/sTDDFT of Grimme and co-workers
•PBEh-3c method of Grimme and co-workers

SCF, DFT and Hessian:
•Large performance improvements for calculations with four center integrals
•Improved performance with RI-J with conventionally stored integrals
•Gradient for range separated hybrids
•Gradient for range double hybrid functionals with meta GGAs
•Gradient for range double hybrid functionals with range separated functionals
•Gradient for RI-JK
•Frequencies for range separated functionals
•Stability analysis and automatic search for broken symmetry states
•Local spin analysis
•Fractional occupation number analysis (FOD) for detection of MR character

MDCI module:
•All improvements for DLPNO methods as listed above
•Closed shell EOM-CCSD energies
•Closed shell STEOM-CCSD energies
•Automatic closed shell STEOM-CCSD active space selection
•EOM-CCSD(2) and STEOM-CCSD(2) approximations
•EOM-CCSD transition moments
•EOM/STEOM-CCSD core level excited states
•ADC(2) method (initial implementation)
•Improved automatic frozen core handling
•Core-correlation in automatic basis set extrapolation

AUTOCI module:
•FIC-MRCI, CEPA/0 variant and DDCI3

•Detailed tutorial showing CASSCF/NEVPT2 usage
•Accelerated CI (ACCCI) a more efficient CI step for multi-root calculations
•Automatic implementation of AbInitio ligand-field theory
•Simplified generation of double-shell orbitals
•Active space protection scheme and improved warnings
•ICE-CI as CI solver for larger active spaces
•Partially Contracted NEVPT2 with and without RI
•Updated interface to BLOCK 1.0
•DMRG-NEVPT2 for active spaces up to 20 orbitals
•Magnetization and magnetic susceptibility
•Printing of the wavefunction in terms of CSFs and spin-determinants
•MREOM-CCSD (also with SOC)
•Local spin analysis for CASSCF
•Fragment decomposition of the spin-spin interaction
•Cumulant approximation for NEVPT2
•Explicitly correlated RI-FIC-NEVPT2 (NEVPT2-F12)

•Full TD-DFT for hybrid functionals
•Gradient for full TD-DFT with hybrid functionals
•TD-DFT/TDA gradient with range separated functionals
•ROCIS magnetic properties (hyperfine, g-tensor, ZFS tensor, MCD)
•ROCIS-RIXS spectra
•PNO-ROCIS for spectacular performance improvements
•Super-fast approximate TD-DFT: sTDA/sTDDFT
•Natural transition orbitals in TD-DFT and ROCIS

•GIAO implementation for NMR chemical shifts. Various aproximations (RIJOCOSX, RIJK)
•New Handling of basis set names. Now fully consistent with TurboMole def2-defaults (including ECPs) SARC basis sets separately available
•New reading of basis sets and ECPs together
•New correlation consistent basis sets added
•New SARC basis sets for the lanthanides; good for correlated calculations
•New ANO-RCC basis sets added
•Improved frozen core handling in correlation calculations
•Improved automatic auxiliary basis set generation
•Corrections for low-frequency modes in thermochemistry
•New and improved NBO interface
•CPCM and full implementation of SMD solvent models
•Intrinsic atomic orbital (IAO) and bond orbital implementation
•Improved performance in Boys localization
•Updated and improved mapspc program
•Atomic Mean Field (AMFI) spin-orbit coupling operators
•EPRNMR works with range separated hybrid functionals
•New molecular dynamics module