3. Model Chemistries

Model Chemistries

• 3.1. Wavefunction Types: RHF/RKS, UHF/UKS, ROKS and more
  • 3.1.1. ROHF Options
  • 3.1.2. UHF Natural Orbitals
  • 3.1.3. UNO, UCO and QROs input
• 3.2. Hartree Fock Theory
• 3.3. Density Functional Theory (DFT)
  • 3.3.1. Basic Usage
  • 3.3.2. Local Functionals
  • 3.3.3. Gradient Corrected Functionals: (meta-)GGAs
    • 3.3.3.1. Customization of Basic Functionals
  • 3.3.4. Hybrid DFT
    • 3.3.4.1. Global Hybrid Functionals
      • 3.3.4.1.1. Customization of Global Hybrids
    • 3.3.4.2. Range-Separated Hybrid Functionals
      • 3.3.4.2.1. Customizing Range-Separated Hybrids
  • 3.3.5. Double-Hybrid DFT
    • 3.3.5.1. Global Double-Hybrid Functionals
    • 3.3.5.2. Range-Separated Double-Hybrid Functionals
      • 3.3.5.2.1. \(\omega\)B97M(2)
    • 3.3.5.3. Customization of Double-Hybrids
  • 3.3.6. LibXC Functional Library
    • 3.3.6.1. Screening Thresholds
    • 3.3.6.2. Modifying LibXC Functional Parameters
    • 3.3.6.3. Simple Input of LibXC Functionals
• 3.4. Dispersion Corrections
  • 3.4.1. Grimme’s DFT-D3 and DFT-D4
    • 3.4.1.1. Damping Functions
    • 3.4.1.2. Three-body term
    • 3.4.1.3. Basic Usage
    • 3.4.1.4. Custom parameters
    • 3.4.1.5. Example
    • 3.4.1.6. Keywords
    • 3.4.1.7. Available Parameters
  • 3.4.2. Non-Local Dispersion Correction (VV10): DFT-NL
    • 3.4.2.1. Basic usage
    • 3.4.2.2. Custom parameters
    • 3.4.2.3. Example
    • 3.4.2.4. Keywords
• 3.5. Semiempirical Methods
  • 3.5.1. Neglect of Differential Overlap: CNDO, INDO, NDDO
    • 3.5.1.1. Basic Usage
    • 3.5.1.2. Custom Parameters
    • 3.5.1.3. Keywords
  • 3.5.2. Extended Tight-Binding: GFN0-xTB, GFN-xTB, GFN2-xTB
    • 3.5.2.1. Solvation in xTB
    • 3.5.2.2. Keywords
  • 3.5.3. Native GFN-xTB and GFN2-xTB
    • 3.5.3.1. Custom parameterization
    • 3.5.3.2. Spin-polarized native xTB
    • 3.5.3.3. SCF with native xTB
    • 3.5.3.4. FOD with native xTB
    • 3.5.3.5. Solvation in native xTB
    • 3.5.3.6. Keywords
• 3.6. Composite Methods (3c methods)
  • 3.6.1. HF-3c
  • 3.6.2. B97-3c
  • 3.6.3. \(r^2\)SCAN-3c
  • 3.6.4. PBEh-3c
  • 3.6.5. B3LYP-3c
  • 3.6.6. \(\omega\)B97X-3c
  • 3.6.7. Keywords
• 3.7. Analytic Density Functional Theory (ADFT)
• 3.8. Random Phase Approximation (RPA)
• 3.9. Perturbation Theory - MP2
  • 3.9.1. Standard (non-RI) MP2
  • 3.9.2. RI-MP2
  • 3.9.3. Calculating MP2 and RI-MP2 Energies
  • 3.9.4. Frozen Core Options
  • 3.9.5. MP2 and RI-MP2 Gradients
  • 3.9.6. RIJCOSX-RI-MP2 Gradients
  • 3.9.7. MP2 and RI-MP2 Second Derivatives
  • 3.9.8. MP2 Properties, Densities and Natural Orbitals
  • 3.9.9. RI-MP2 and Double-Hybrid DFT Response Properties
  • 3.9.10. Local MP2 calculations (DLPNO-MP2)
  • 3.9.11. Local MP2 gradients
  • 3.9.12. Local MP2 Second Derivatives and Response Properties
  • 3.9.13. Numerical DLPNO-MP2 derivatives
  • 3.9.14. Multi-Level DLPNO-MP2 calculations
  • 3.9.15. Explicitly correlated MP2 calculations
  • 3.9.16. MP2 in “Double-Hybrid” Density Functional Theory
  • 3.9.17. Orbital Optimized MP2 Methods
    • 3.9.17.1. OO-MP2 Theory
    • 3.9.17.2. OO-MP2 - Tips, Usage and Examples
  • 3.9.18. Regularized MP2 and RI-MP2
  • 3.9.19. Keywords
• 3.10. Coupled Cluster and CI Theories (MDCI)
  • 3.10.1. Theory
    • 3.10.1.1. Closed-Shell Equations
    • 3.10.1.2. Open-Shell Equations
  • 3.10.2. Basic Usage
    • 3.10.2.1. Frozen Core Options
    • 3.10.2.2. The singles Fock term
  • 3.10.3. Coupled-Cluster Densities
  • 3.10.4. Static versus Dynamic Correlation
  • 3.10.5. Basis Sets for Correlated Calculations. The case of ANOs.
  • 3.10.6. The Coupled Cluster S-Diagnostic
  • 3.10.7. Explicitly Correlated Methods: F12-MP2 and F12-CCSD(T)
  • 3.10.8. Automatic extrapolation to the basis set limit
  • 3.10.9. Cluster in molecules (CIM)
  • 3.10.10. Local correlation (DLPNO)
    • 3.10.10.1. Basic Usage
    • 3.10.10.2. Keywords
    • 3.10.10.3. Including (semi)core orbitals in the correlation treatment
  • 3.10.11. Multi-Level Calculations
  • 3.10.12. Multi-Level Calculations for IP and EA-EOM-DLPNO-CCSD
  • 3.10.13. Excited States (EOM/STEOM/ADC)
  • 3.10.14. Keywords
• 3.11. Correlated Methods using Automatic Code Generation (AUTOCI)
  • 3.11.1. Introduction
  • 3.11.2. Basis Usage / List of Features
  • 3.11.3. Analytic Nuclear Gradients with AUTOCI
  • 3.11.4. AUTOCI Response Properties via Analytic Derivatives
    • 3.11.4.1. Unperturbed Parameters
    • 3.11.4.2. Perturbed Parameters
    • 3.11.4.3. Orbital Relaxation
    • 3.11.4.4. Input Options
    • 3.11.4.5. Input Examples
  • 3.11.5. Fully Internally Contracted MRCI (FIC-MRCI)
    • 3.11.5.1. Input Example
  • 3.11.6. Fully Internally Contracted MRCC (FIC-MRCC)
    • 3.11.6.1. Input Example
  • 3.11.7. Fully Internally Contracted NEVPT (FIC-NEVPT4(SD)/FIC-NEVPT3/FIC-NEVPT2)
    • 3.11.7.1. FIC-NEVPT3
    • 3.11.7.2. FIC-NEVPT4(SD)
    • 3.11.7.3. Input Example
  • 3.11.8. FIC Ansatz: Unrelaxed Densities and Natural Orbitals
  • 3.11.9. Keywords
• 3.12. Arbitrary Order Coupled-Cluster (MRCC interface)
• 3.13. Complete and Incomplete Active Space Self-Consistent Field (CASSCF and RAS/ORMAS)
  • 3.13.1. Introduction
  • 3.13.2. Theory
    • 3.13.2.1. Optimization of CASSCF wave functions
    • 3.13.2.2. State-averaging
  • 3.13.3. Basic Usage
    • 3.13.3.1. Orbital Optimization (2-step approach)
      • 3.13.3.1.1. Incremental Fock
      • 3.13.3.1.2. Monitoring the active space
    • 3.13.3.2. Orbital Optimization (1-step approach): Robust Convergence with TRAH-CASSCF
    • 3.13.3.3. Using the RI Approximation
    • 3.13.3.4. Final Orbitals: Canonicalization Choices
    • 3.13.3.5. CI Solvers (CSFCI, ACCCI, …, ICE)
    • 3.13.3.6. Model Spaces: CAS, RAS and ORMAS
      • 3.13.3.6.1. Arbitrary References
    • 3.13.3.7. Restricted Active Space (RAS)
    • 3.13.3.8. Occupation Restricted Multiple Active Spaces (ORMAS)
    • 3.13.3.9. The RASCI and ORMAS Module
  • 3.13.4. Keywords
  • 3.13.5. A simple Example: Be Ground State
  • 3.13.6. Guess: Natural Orbitals Example
  • 3.13.7. Guess: Atomic Valence Active Space (AVAS)
  • 3.13.8. Example: Symmetry
  • 3.13.9. Example: Breaking Chemical Bonds
  • 3.13.10. Example: Excited States
  • 3.13.11. Example: Large Active Spaces using ICE-CI
  • 3.13.12. Example: Geometry Optimization
  • 3.13.13. Example: Natural Orbitals as Input for Coupled-Cluster Calculations
  • 3.13.14. CASSCF Densities
  • 3.13.15. CASSCF Properties
  • 3.13.16. 1- and 2-shell Abinitio Ligand Field Theory (AILFT)
  • 3.13.17. Extended Space Ab initio Ligand Field Theory (ESAILFT)
  • 3.13.18. Core Excited Spectra: CAS-CI/RAS-CI XAS/RIXS
  • 3.13.19. Core Excited Spectra: CAS-CI/RAS-CI XES
• 3.14. Approximate Full CI Calculations in Subspace: ICE-CI
  • 3.14.1. Introduction
  • 3.14.2. The ICE-CI and CIPSI Algorithms
  • 3.14.3. A Simple Example Calculation
  • 3.14.4. Accuracy
  • 3.14.5. Scaling behavior
  • 3.14.6. Accuracy of the Wavefunction
  • 3.14.7. Potential Energy Surfaces
  • 3.14.8. Excited States
  • 3.14.9. Tips and Tricks
  • 3.14.10. Large-scale approximate CASSCF: ICE-SCF
  • 3.14.11. Keywords
  • 3.14.12. A Technical Note: orcacclib
• 3.15. Density Matrix Renormalization Group (DMRG)
  • 3.15.1. Technical capabilities
  • 3.15.2. How to cite
  • 3.15.3. Basic Usage
    • 3.15.3.1. Orbital optimization
    • 3.15.3.2. Advanced options
    • 3.15.3.3. Troubleshooting
  • 3.15.4. Keywords
  • 3.15.5. Example: Porphine \(\pi\)-active space calculation
• 3.16. N-Electron Valence State Perturbation Theory (NEVPT2)
  • 3.16.1. A simple Example: \(N_2\) Ground State
  • 3.16.2. RI, RIJK and RIJCOSX Approximation
  • 3.16.3. Beyond the RI approximation: DLPNO-NEVPT2
  • 3.16.4. Explicit Correlation: NEVPT2-F12 and DLPNO-NEVPT2-F12
  • 3.16.5. Handling of Reduced Density Matrices
    • 3.16.5.1. PS Approximation (default)
    • 3.16.5.2. Cumulant Approximation (optional)
  • 3.16.6. False Intruder States and Imaginary Shift
  • 3.16.7. Large Active Spaces: ICE-NEVPT2
  • 3.16.8. Large Active Spaces: DMRG-NEVPT2
  • 3.16.9. Selecting or Specific States for NEVPT2
  • 3.16.10. Unrelaxed Densities and Natural Orbitals
  • 3.16.11. State-averaged SC-NEVPT2
  • 3.16.12. Quasi-Degenerate SC-NEVPT2
  • 3.16.13. Keywords
• 3.17. Complete Active Space Peturbation Theory (CASPT2 and CASPT2-K)
  • 3.17.1. Example Nitrogen molecule
  • 3.17.2. Keywords
• 3.18. CASSCF and DFT
  • 3.18.1. General Description
    • 3.18.1.1. Multi-Configurational Pair Density Functional Theory
    • 3.18.1.2. Long-Range CASSCF Short-Range DFT
  • 3.18.2. Computational Aspects
  • 3.18.3. Excited States
• 3.19. Multireference Configuration Interaction and Pertubation Theory (uncontracted)
  • 3.19.1. Introductory Remarks
  • 3.19.2. RI-approximation
  • 3.19.3. Individual Selection
    • 3.19.3.1. Single excitations
    • 3.19.3.2. Reference Spaces
    • 3.19.3.3. Size Consistency
    • 3.19.3.4. Performance
    • 3.19.3.5. Symmetry
  • 3.19.4. A Tutorial Type Example of a MR Calculation
  • 3.19.5. Excitation Energies between Different Multiplicities
  • 3.19.6. Correlation Energies
  • 3.19.7. Thresholds
    • 3.19.7.1. Reference Values for Total Energies
    • 3.19.7.2. Convergence of Single Reference Approaches with Respect to T\(_{\text{sel} }\)
    • 3.19.7.3. Convergence of Multireference Approaches with Respect to T\(_{\text{pre} }\)
  • 3.19.8. Energy Differences - Bond Breaking
  • 3.19.9. Energy Differences - Spin Flipping
  • 3.19.10. Potential Energy Surfaces
  • 3.19.11. Multireference Systems - Ozone
  • 3.19.12. Size Consistency
  • 3.19.13. Efficient MR-MP2 Calculations for Larger Molecules
  • 3.19.14. Properties Calculation Using the SOC Submodule
    • 3.19.14.1. Zero-Field Splitting
    • 3.19.14.2. Local Zero-Field Splitting
    • 3.19.14.3. Zero-Field Splitting from an excited Multiplet
    • 3.19.14.4. g-Tensor
    • 3.19.14.5. Magnetization and Magnetic Susceptibility
    • 3.19.14.6. MCD and Absorption Spectra
    • 3.19.14.7. Addition of Magnetic Fields
    • 3.19.14.8. Relativistic Picture Change in Douglas-Kroll-Hess SOC and Zeeman Operators
    • 3.19.14.9. X-ray Spectroscopy
  • 3.19.15. Keywords
• 3.20. Multireference Equation of Motion Coupled-Cluster (MR-EOM-CC)
  • 3.20.1. A Simple MR-EOM-CC Calculation
  • 3.20.2. Capabilities
  • 3.20.3. Perturbative MR-EOM-CCPT
  • 3.20.4. Details on the Multireference Equation of Motion Coupled-Cluster (MR-EOM-CC ) Theory
    • 3.20.4.1. The Steps Required to Run an MR-EOM-CC Calculation
      • 3.20.4.1.1. State-Averaged CASSCF Calculation
      • 3.20.4.1.2. Selection of the States to Include in the MR-EOM-CC Calculation
      • 3.20.4.1.3. Running the MR-EOM-CC Calculation
    • 3.20.4.2. Approximate Inclusion of Spin-Orbit Coupling Effects in MR-EOM-CC Calculations
    • 3.20.4.3. A Projection/Singular PT Scheme to Overcome Convergence Issues in the T Amplitude Iterations
  • 3.20.5. An Orbital Selection Scheme for More Efficient Calculations of Excitation Spectra with MR-EOM
  • 3.20.6. Nearly Size Consistent Results with MR-EOM-CC by Employing an MR-CEPA(0) Shift in the Final Diagonalization Procedure
  • 3.20.7. Perturbative MR-EOM-CCPT
• 3.21. Dynamic Correlation Dressed CAS
  • 3.21.1. Theory of Nonrelativistic DCD-CAS(2)
  • 3.21.2. Treatment of spin-dependent effects
  • 3.21.3. Simple example
  • 3.21.4. List of keywords
• 3.22. Full Configuration Interaction
• 3.23. Molecular Mechanics
  • 3.23.1. Combining the MM module with other ORCA Features
  • 3.23.2. Molecular Mechanics Force Field in ORCA
    • 3.23.2.1. Supported Force Field Types
    • 3.23.2.2. How to generate and manipulate the ORCA Force Field File
      • 3.23.2.2.1. Conversion from other formats to ORCAFF.prms: convff
      • 3.23.2.2.2. Divide a force field file: splitff
      • 3.23.2.2.3. Merge force field files: mergeff
      • 3.23.2.2.4. Repeat force field files: repeatff
      • 3.23.2.2.5. Divide a PDB file: splitpdb
      • 3.23.2.2.6. Merge PDB files: mergepdb
      • 3.23.2.2.7. Create simple force field: makeff
      • 3.23.2.2.8. Get standard hydrogen bond lengths: getHDist
      • 3.23.2.2.9. Create ORCAFF.prms file for IONIC-CRYSTAL-QMMM
  • 3.23.3. Speeding Up Nonbonded Interaction Calculation
    • 3.23.3.1. Force Switching for LJ Interaction
    • 3.23.3.2. Force Shifting for Electrostatic Interaction
    • 3.23.3.3. Neglecting Nonbonded Interactions Within Non-Active Region
  • 3.23.4. Rigid Waters
  • 3.23.5. Available Keywords for the MM module