Skip to content

CASSCF

Keywords of the CASSCF input block

Keyword Format Description Default
NEl (ActEl) integer The number of active electrons. 0
NOrb (ActOrb) integer The number of active orbitals. 0
ConfImportanceThrs double Threshold for printing out CI-configurations with the corresponding leading coefficient. 5e-2
DavidsonAHPCDim integer Dimension of the augmented Hessian Davidson preconditioner used in NR and FNR. More specifically, the number of internal/virtual orbital pairs with lowest energy differences. Based on https://doi.org/10.1063/5.0090447. 256
DIISDim integer The number of SCF cycles the DIIS takes into account. 5
DIISFac double A factor with which all diagonal entries in the DIIS matrix are multiplied except for the the one corresponding to the lowest energy. 1.05
DoASSIST bool If set to true the density of the SC-NEVPT first order interacting space (and the quasi-natural orbitals) are evaluated. Can also be invoked by DOASS1ST.7 false
DoNEVPT2 bool If set to true a SC-NEVPT2 calculation is conducted after the CASSCF procedure.1,2,3 false
DoSOC bool If set to true, a Spin-Orbit Coupling calculation is done. false
StoreSOCMatrices bool If set to true, SOC-, s-, l-, and p-matrices will be stored. false
DoQDNEVPT2 bool If set to true a quasi-degenerate SC-NEVPT24 calculation is conducted after the CASSCF procedure. false
ETol double  The energy convergence tolerance of the orbital optimization. 1.0e-07
FinalActOrbs string Defines the type of active orbitals after the last iteration. Available options: unchanged, natural. unchanged
CISolver string Specifies the active-space solver. Can be , FCI, HCI or GCI (experimental). FCI
FullConvergence bool If set to false, convergence is only signaled when either the \(E_{tol}\) and \(G_{tol}\) convergence criteria are fulfilled. true
GTensor bool If set to true, the g-tensor is calculated. DoSOC must be set to true false
GTol double The gradient norm convergence tolerance of the orbital optimization. 1.0e- 04
IPEAShift bool If set true a CASPT2-type approximate denominator together with a IPEA shift is used for the ASS1ST procedure true
IPEAShiftValue double The value of IPEA shift used in the ASS1ST procedure. 0.25
MaxNTrialVecs integer Maximum dimension of the Davidson expansion space. 500
MaxIter integer The maximum number of orbital optimization iterations. 50
NRoots vector(integer) The number of calculated roots for each multiplicity. 1
OrbOrderType string  Defines the type of order the active orbitals are in during the procedure. Available options: none, Fiedler, Generic. None
OrbStep string Defines the orbital optimization technique. Available Options: NR, DIIS, FNR, SuperCIPTDIIS.8,9,10,11,12,13,14 SuperCIPTDIIS
OutputLevel integer The level of output given by the BLOCK program ranging from -1 to 2. A higher number corresponds to a more detailed output. 0
PrintWeightThresh double The weight threshold for printing a contribution in the state composition output. 0.01
PTCanonStep string or integer Determines the way that molecular orbitals and their energies are generated prior to NEVPT2 calculations. Options are SA or 0 for state-averaged orbitals and SS or 1 for state-specifically canonicalized orbitals. sa
LevelShiftDn double An artificial shift of the occupied orbital energies (in a.u.) to improve convergence of the SCF procedure. 1.0
LevelShiftUp double An artificial shift of the virtual orbital energies (in a.u.) to improve convergence of the SCF procedure. 1.0
NRMaxIter integer The maximum number of iterations during the numerical Davidson diagonalization of the Hessian matrix during the Newton-Raphson procedure. 50
NRGuessMatDim integer The dimension of the guess matrix used in the Davidson routine during the Newton-Raphson procedure. 256
NRTol double Residual norm convergence tolerance used in the Davidson routine during the Newton-Raphson procedure. 1.0e-5
QDNEVPT2Type string Determines the way the effective QD-NEVPT2 matrix is diagonalized. Possible options are VanVleck5, Cloizeaux6 or Bloch.15 VanVleck
ReadMatricesOnly bool If set to true, the CASSCF step is skipped and only preexisting density matrices are read in. To be used together with WRITEMATRICESONLY in a pair of calculations. (See sample input) false
SwitchOrbStep string The orbital optimization step that is used close to convergence. SuperCIPTDIIS
SwitchOrbStepThresh double  The gradient norm at which the orbital optimization technique is switched. 0.03
TrustRadius double Maximum norm of the orbital step that can be taken by second order NR and FNR methods. 0.5
TrustRadiusScaling double Scaling factor applied to the trust radius in the FNR orbital optimization method to force convergence. 0.7
UsePrevCFGsThrs double Threshold for the orbital gradient norm to use previous steps configurations in HCISCF. 5e-4
Weights vector(double) The weight of each root within the state-averaging procedure. For calculations with multiple spin states, the weights need to be given in the same order as in the input of the spin multiplicities. If the sum of all weights does not match 1, the weights will be renormalized to 1. By default each root has an equal weight. 1
WriteMatricesOnly bool If set to true, postprocessing steps (e.g. NEVPT2) are skipped and only density matrices are stored on disk. To be used together with READMATRICESONLY in a pair of calculations. (See sample input) false
ReadExtHOrcaJSON bool If set to true, the one-electron Hamiltonian will be read from an Orca .json file. false
CalcSSGrad integer Requests calculation of the state-specific MCSCF nuclear gradient. The argument is the index (root) of the state for which the gradient is calculated. 0
CalcSAGrad integer Requests calculation of the state-averaged MCSCF nuclear gradient. The argument is the index (root) of the state for which the gradient is calculated. 0
CalcNAC bool If set to true, the SA-CASSCF non-adiabatic couplings will be calculated. false
CalcCIOptGrad bool If set to true, the conical intersection optimization gradient will be calculated. true
NRRTol double Threshold for signaling microiterations convergence in NR and FNR methods. 1.0e-05
PCGThresh double Residual threshold for signaling convergence of the PCG algorithm. 1e-05
PCGMaxIter int Maximum number of preconditioner conjugate-gradient (PCG) iterations. 100
DoENEVPT2 bool If set to true a NEVPT2 calculation with the Epstein-Nesbet 0th order Hamiltonian for the Va and Vi classes will be conducted. Works for HCI only. false
DoNEVPT2Residuals bool If set to true, the residuals will be calculated in HCI-NEVPT2. true
DoAC0 bool If set to true an AC0 calculation is conducted after the CASSCF procedure.16 false

  1. C. Angeli, R. Cimiraglia, S. Evangelisti, T. Leininger, J. Malrieu, J. Chem. Phys. 2001, 114, 10252. ↩

  2. C. Angeli, R. Cimiraglia, J. Malrieu, J. Chem. Phys. 2002, 117, 9138. ↩

  3. S. Guo, M. A. Watson, W. Hu, Q. Sun, G. K.-L. Chan, J. Chem. Theory Comput. 2016, 12, 1583–1591. ↩

  4. C. Angeli, S. Borini, M. Cestari, R. Cimiraglia, J. Chem. Phys. 2004, 121, 4043–4049. ↩

  5. I. Shavitt, L. T. Redmon, J. Chem. Phys. 1980, 73, 5711–5717. ↩

  6. J. Des Cloizeaux, Nucl. Phys. 1960, 20, 321–346. ↩

  7. A. Khedkar, M. Roemelt, J. Chem. Theory Comput. 2019, 15, 3522–3536. ↩

  8. B. O. Roos, P. R. Taylor, P. E. Si, et al., Chem. Phys. 1980, 48, 157–173. ↩

  9. C. Angeli, S. Evangelisti, R. Cimiraglia, D. Maynau, J. Chem. Phys. 2002, 117, 10525–10533. ↩

  10. C. Kollmar, K. Sivalingam, B. Helmich-Paris, C. Angeli, F. Neese, J. Comput. Chem. 2019, 40, 1463–1470. ↩

  11. P. Pulay, Chem. Phys. Lett. 1980, 73, 393–398. ↩

  12. P. Pulay, J. Comput. Chem. 1982, 3, 556–560. ↩

  13. U Meier, V Staemmler, Theor. Chim. Acta 1989, 76, 95–111. ↩

  14. P. E. Siegbahn, J. Almlöf, A. Heiberg, B. O. Roos, J. Chem. Phys. 1981, 74, 2384–2396. ↩

  15. C. Bloch, Nucl. Phys. 1958, 6, 329–347. ↩

  16. Y. Guo, K. Pernal, Faraday Discuss. 2024, 254, 332–358. ↩