# ORCA 6 Changes

## ORCA 6.0 Highlights

### SCF and Single Reference 

-   LeanSCF: reduced memory, more robust convergence
-   Electric field optimizations
-   General ROHF implementation (SCF/Gradient) with all approximations
-   General CSF ROHF
-   New density functionals
-   Delta-SCF
-   UHF STEOM-CCSD
-   UHF-IP-EOM-CCSD
-   UHF-EA-EOM-CCSD
-   Regularized MP2
-   Regularized OOMP2
-   Solvation in OOMP2
-   Improved stability analysis featuring all approximations, solvation etc
-   MixGuess to converge to biradicaloid open shell singlet type broken symmetry solutions
-   Approximate Spin Projection Method for broken symmetry calculations (SCF/Gradient)

### Multi Reference 

-   TRAH, AVAS, MCRPA
-   Linear response CASSCF
-   Vastly improved Recursive CI coupling coefficient generation

### Automatic Code generation

-   MPn
-   CCSD(T) gradients
-   CCSDT

### Relativity 

-   X2C
-   New and consistent DKH infrastructure

### Solvation & Embedding 

-   DLPNO-CCSD(T) PTES Approach
-   SMD analytical Hessian
-   Dynamically adjusted radii: DRACO
-   Improved surface grids
-   Interface to openCOSMO-RS
-   Explicit Solvator
-   Molecule Docker
-   FMM implementation for embedding
-   CIM implementation works with DLPNO-CC, DLPNO-MP2

### Optimization 

-   More robust optimizer (fewer cycles, fewer cases with negative frequencies)
-   GOAT global optimizer and conformer generator
-   Basis set limit extrapolated optimizations through compound scripts
-   Extrapolation with counterpoise correction through compound scripts

### Hessian 

-   Group parallelization
-   Performance improvements

### Excited States

-   Analytical gradient for meta-GGA functionals

### New Spectroscopic Properties 

-   VCD implementation at the SCF level
-   MCD with vibronic structure
-   General spin ROCIS
-   Higher order moments and exact field matter coupling
-   Spin rotation constants

### Misc Properties 

-   Local dipole moments and polarizabilities
-   Frequency dependent electric properties
-   VPT2 enhancements
-   Restructured NMR simulation program `orca_nmrspectrum`
-   MBIS charges

### Workflow & Interfacing 

-   Property file: Machine readable, Human readable summary of ORCA run
-   Compound: vastly improved Syntax, features, optimizations, ...
-   `orca_2json`: generate integrals, property file, run backwards to get MOs into ORCA
-   Citation tool for helping find the right references

For a detailed change log of ORCA 6.0, please see the [detailed change log](/contents/detailedchangelog.md)