Provided by: psi3_3.4.0-6build3_amd64

**NAME**

detcas - Determinant Configuration Interaction / Complete Active Space Self-Consistent-Field Program

**DESCRIPTION**

The programdetcasperforms a complete-active-space self-consistent-field (CASSCF) optimization of molecular orbitals via a two-step procedure in conjunction with the determinant configuration interaction program DETCI. The program is fairly simple and currently uses a Newton-Raphson approach to update the orbitals, employing a simple approximate orbital Hessian. Convergence is accelerated using Pulay's direct inversion of the iterative subspace (DIIS) procedure. The code has been written to allow more general wavefunctions that do not necessarily feature a full CI treatment of the active space. In particular, any restricted active space (RAS) CI wavefunction supported by DETCI can be used, allowing MCSCF wavefunctions of the RASSCF type.

**REFERENCES**

Approximate Orbital Hessian: 1. G. Chaban, M. W. Schmidt, and M. S. Gordon, Theor. Chim. Acta 97, 88-95 (1997). Restricted Active Space CI: 1. Determinant Based Configuration Interaction Algorithms for Complete and Restricted Configuration Interaction Spaces, J. Olsen, B. O. Roos, P. Jorgensen, and H. J. Aa. Jensen, J. Chem. Phys. 89, 2185 (1988). Restricted Active Space SCF: 1. P.-A. Malmqvist, A. Rendell, and B. O. Roos, J. Phys. Chem. 94, 5477 (1990). DETCI Program: 1. C. D. Sherrill, Computational Algorithms for Large-Scale Full and Multi-Reference Configuration Interaction Wavefunctions, PhD thesis, University of Georgia, Athens, GA, 1996. 2. C. D. Sherrill and H. F. Schaefer, The Configuration Interaction Method: Advances in Highly Correlated Approaches, Adv. Quantum Chem. 34, 143-269 (1999).

**FILES** **REQUIRED**

input.dat - Input file file78 - MO one-electron integrals (fzc operator) file72 - MO two-electron integrals file73 - MO one-particle density matrix file74 - MO two-particle density matrix file75 - MO Lagrangian

**FILES** **UPDATED**

output.dat - Output file file14.dat - Record of energies and orbital gradients

**INPUT** **FORMAT**

The following command-line arguments are available:-quietThis gives the same result asPRINT=0.-ofnameGives the filename for the output file. Defaults to output.dat. Additional input for this program is read from the file input.dat. The more commonly used keywords are:WFN=stringThe supported wave function types are CASSCF and RASSCF.CONVERGENCE=integerConvergence desired on the orbital gradient. Convergence is achieved when the RMS of the error in the orbital gradient is less than 10**(-n). The default is 4 for energy calculations and 7 for gradients.DOCC=integer_arrayThis vector gives the number of doubly occupied orbitals in each irrep. There is no default.SOCC=integer_arrayThis vector gives the number of singly occupied orbitals in each irrep. There is no default.ENERGY_CONVERGENCE=integerConvergence desired on the total MCSCF energy. The default is 7.FROZEN_DOCC=integer_arrayThe number of lowest energy doubly occupied orbitals in each irreducible representation which will literally be frozen (not updated in the MCSCF). The Cotton ordering of the irredicible representations is used. The default is the zero vector.FROZEN_UOCC=integer_vectorThe number of highest energy unoccupied orbitals in each irreducible representation which will literally be frozen (not updated in the MCSCF). The default is the zero vector.RESTRICTED_DOCC=integer_arrayThe number of lowest energy doubly occupied orbitals in each irreducible representation which will be optimized but kept doubly occupied in the MCSCF. These orbitals come after theFROZEN_DOCCorbitals. The default is the zero vector.RESTRICTED_UOCC=integer_arrayThe number of highest energy unoccupied orbitals in each irreducible representation which will be optimized but kept unoccupied in the MCSCF. These orbitals come before theFROZEN_UOCCorbitals. The default is the zero vector.NCASITER=integerMaximum number of iterations to optimize the orbitals. This optionshouldbespecifiedintheDEFAULTsectionofinput, because it needs to be visible to the control program PSI. Defaults to 1.=integerThis option determines the verbosity of the output. A value of 1 or 2 specifies minimal printing, a value of 3 specifies verbose printing. Values of 4 or 5 are used for debugging. Do not use level 5 unless the test case is very small (e.g. STO H2O CISD). The less commonly used keywords are:DIIS_FREQ=integerThe DIIS extrapolation procedure will be attempted everyniterations. The default is 1.DIIS_MAX_VECS=integerThe maximum number of subspace vectors for the DIIS procedure. After this number of vectors are reached, older vectors will be dropped from the subspace as necessary. The default is 8.DIIS_MIN_VECS=integerThe minimum number of subspace vectors before a DIIS interpolation can be performed. The default is 2. It doesn't make sense to have values less than 2.DIIS_START=integerThe iteration number when Pulay's Direct Inversion of the Iterative Subspace (DIIS) procedure for acceleration of convergence should be turned on. The default is 3. Prior to this iteration, vectors are not added to the DIIS subspace. The first DIIS step will not be taken untilDIIS_MIN_VECSvectors are in the DIIS subspace.LAG_FILE=integerFile (unit number) for reading the lagrangian matrix. The default value is currently 75.OPDM_FILE=integerFile (unit number) for reading the one-particle density matrix. The default value is currently 73.SCALE_GRAD=booleanTells whether to scale the orbital gradient by the approximate (diagonal) orbital Hessian. The default is TRUE.SCALE_STEP=realScale factor for the orbital rotation step. Default is 1.0.TPDM_FILE=integerFile (unit number) for reading the two-particle density matrix. The default value is currently 74.LEVEL_SHIFT=booleanTells whether to allow for level shifting of the hessian matrix. This can be used to ensure that the hessian is positive definite for the beginning iterations. If the hessian is not positive definite near convergence, then this may be a sign of numerical instabilities in the MCSCF. The default is TRUE.SHIFT=realTells how much the diagonal elements of the hessian should be shifted for level shifting. Default is 0.01.DETERM_MIN=realMinimum allowed valued for the determinant of the hessian matrix if level shifting is on. This is not used if LEVEL_SHIFT=FALSE. Default is 0.00001.STEP_MAX=realThis is the maximum allowed single orbital rotation. Default is 0.30.FORCE_STEP=booleanThis allows the user to overide the calculated step and to force a step in a particular direction. This can be useful if trying to force the calculation away from a saddle point. The default is FALSE.FORCE_PAIR=integerThis is the index for the independent pair which is to be rotated if FORCE_STEP=TRUE. This is ignored otherwise. There is no default.FORCE_VALUE=realThis is the orbital rotation value for rotating the orbitals specified by FORCE_PAIR. This is only used if FORCE_STEP is set to TRUE. The default value is 0.0.CHECK_HESSIAN=booleanCalculate the eigenvalues of the orbital hessian. This is good for checking for saddle-point solutions. Should be used without level shifting. The default is FALSE.EIGEN_VECTORS=booleanDo you want to calculate the eigenvectors of the orbital hessian as well. This is ignored if CHECK_HESSIAN=FALSE. Default is FALSE. 8 May, 1998 detcas(1)