# ORCA 4.2 released

09 08 19 - Filed in: computational chemistry

ORCA is a general purpose quantum chemistry package that is free of charge for academic users. It has been developed since the late 90s and by now is one of the most heavily used quantum chemistry packages worldwide. It can be downloaded from the Website of the Max Planck Institut fuer Kohlenforschung at www.kofo.mpg.de

Commercial users should contact https://www.faccts.de/orca/

With a strong user base of more than 15.000 registered users in academia worldwide, ORCA is the fastest growing quantum-chemical software package to date. ORCA provides cutting-edge methods in the fields of density functional theory as well as correlated wave-function based methods

# ORCA 4.2 New Features

## Local correlation

- Iterative (T) for open shells
- Multi-level scheme for open shell systems (all PNO accuracy levels)
- DLPNO-STEOM-CCSD for closed shells
- DLPNO-CCSD(T)-F12 for open shells
- Automatic fragmentation in LED analysis
- RIJCOSX-LED implementation
- HF-LD method for efficient dispersion energy calculations

## Multi-Reference

- FIC-CASPT2 implementation including level shift and IP/EA shift.
- FIC-NEVPT2 unrelaxed densities and natural orbitals.
- CIPSI/ICE improvements. Can be run now with configurations, individual determinants or CSFs (experimental)
- FIC-ACPF/AQCC: variants of the FIC-MRCI ansatz
- Efficient linear response CASSCF
- Reduced memory requirements in MRCI and CIPSI/ICE

## Spectroscopy

- GIAO EPR calculations (one issue with the SOMF operator still remaining)
- Improvements to ESD module for fluorescence, phosphorescence, bandshape, lifetime and resonance Raman calculations
- ESD now includes also the prediction of the Intersystem Crossing non-radiative rates
- Hyperfine couplings for CASSCF calculations (but not as response)

## Excited states

- Spin-orbit coupling in TD-DFT
- MECP optimization for TD-DFT
- Conical Intersection Optimization
- Range-separated double-hybrids (B2PLYP, B2GPPLYP) for TDDFT
- Numerical and Hellmann-Feynman NACMEs using TD-DFT/CIS
- DLPNO-STEOM-CCSD for closed shells (also see 'Local correlation')

## Solvation

- CPCM Gaussian Charge Scheme with the scaled-vdW surface and the Solvent Excluded Surface (SES). Available for single point energy calculations and geometry optimizations using the analytical gradient.

## SCF/optimizer/semi-empirics/infrastructure etc.

- Nudge elastic band (NEB) transition states improvements (also works with xTB for initial path)
- Improved compound method scripting language for workflow improvements
- Improved ASCII property file
- Libxc interface allows a far wider range of density functionals to be used
- Interfaced with Grimmes GFN-xTB and GFN2-xTB
- Improvement of IRC algorithm
- Cartesian minimization (L-OPT) for systems with 100.000s of atoms, Minimization of specific elements (incl. H) only, fragment specific optimization treatment (relax all, relax hydrogens, rigid fragment, fixed fragments)

## QM/MM and MM

- First release with ORCA-native MM and QM/MM implementation
- Automated conversion from NAMDs CHARMM format
- Automated generation of simple force-field for non-standard molecules
- Simple definition of active and QM regions
- Automated inclusion and placement of link-atoms
- Automated charge-shifts to prevent over-polarization
- MM and QM/MM work with all kinds of optimizations, NEB / NEB-TS methods, frequency analysis
- Option for rigid MM water (TIP3P) in MD simulation and optimization

## Molecular Dynamics

- Added a Cartesian minimization command to the MD module, based on L-BFGS and simulated annealing. Works for large systems (> 10'000 atoms) and also with constraints. Offers a flag to only optimize hydrogen atom positions (for crystal structure refinement).
- The MD module can now write trajectories in DCD file format (in addition to the already implemented XYZ and PDB formats).
- The thermostat is now able to apply temperature ramps during simulation runs.
- Added more flexibility to region definition (can now add/remove atoms to/from existing regions).
- Added two new constraint types which keep centers of mass fixed or keep complete molecules rigid.
- Ability to store the GBW file every n-th step during MD runs (e.g. for plotting orbitals along the trajectory).
- Can now set limit for maximum displacement of any atom in a MD step, which can stabilize dynamics with poor initial structures. Runs can be cleanly aborted by "touch EXIT".
- Better handling/reporting of non-converged SCF during MD runs.
- Fixed an issue which slowed down molecular dynamics after many steps.
- Stefan Grimme's xTB method can now be used in the MD module, allowing fast simulations of large systems.

## Miscellaneous

- Compute thermochemical corrections at different temperatures without recomputing the Hessian
- Fragments can now be defined in the geom block as simple lists
- Simpler input format for definition of atom lists and fragments, in particular useful for large atom lists
- basename.trj files are now called basename_trj.xyz

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