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# cscf

Langue: *en*

Version: *314403 (ubuntu - 07/07/09)*

Section: *1 (Commandes utilisateur)*

## NAME

cscf - solves the Hartree-Fock equations## DESCRIPTION

The program **cscf** carries out the iterative procedure to solve the Hartree-Fock equations.

This program is restricted to D2h symmetry and its subgroups and the orbital occupations are required to be integers. Thus, certain pure angular momentum states derived from partial occupation of degenerate orbitals cannot be obtained with the present codes. For example, the 2PIu (doublet PI u) state of linear O-N-O derived from the lowest energy linear (pi u)1 configuration may only be computed as the 2B2u (doublet B2u) or 2B3u (doublet B 3u) component of the 2PIu (doublet PI u) state, and the resulting spatial wavefunction will not have PI symmetry. In a certain sense, however, this is desirable, as the energy will be a continuous function of the bending angle. Calculating the energy of bent configurations as 2B2u (doublet B 2u) or 2B3u (doublet B 3u) and doing a pure 2PIu (doublet PI u) state at linear geometries results in a pronounced discontinuity.

For the most part, triplet states resulting from double occupation of a doubly degenerate orbital, such as the 3A2 (triplet A 2) state resulting from the (e')2 or (e")2 configurations in D3h symmetry, or the 3SIGMAg (triplet SIGMA g) state of a (pi g)2 or (pi u)2 configuration in Dinfh (D infinity h) symmetry, will have the proper spatial symetry. The singlet states resulting from these same electronic configurations are inherently multiconfiguration and, as such, are not well represented by single configuration wavefunctions.

## REFERENCES

PK-file method:

- 1.
- R. C. Raffenetti, Chem. Phys. Lett. 20 (1973) 335.

Molecular symmetry and closed shell HF calculations:

- 1.
- M.Dupuis, and H.F.King, Int. J. Quant. Chem. 11 (1977) 613.

DIIS for closed shell:

- 1.
- P. Pulay, Chem. Phys. Lett. 73 (1980) 393.
- 2.
- P. Pulay, J. Comp. Chem. 3 (1982) 556.

Coupling coefficients (alpha and beta) for open shell:

- 1.
- C. C. J. Roothaan, Rev. Mod. Phys. 32 (1960) 179.

Damping:

- 1.
- D. R. Hartree, "The Calculation of Atomic Structures" (Wiley: New York) 1957.
- 2.
- M. C. Zerner and M. Hehenberger, Chem. Phys. Lett. 62 (1979) 550.

Level shifting:

- 1.
- V. R. Saunders and I. H. Hillier, Int. J. Quant. Chem. 7 (1973) 699.

## CONVERGING **CSCF**

For difficult open shell cases, it is recommended that an appropriate closed shell calculation be run first (add or remove an extra electron) and that this SCF vector then be used as a guess for the desired open shell wavefunction. For TCSCF cases, it is always wise to run a closed shell (or perhaps the appropriate triplet) SCF first and then use this as a guess for the TCSCF.

For open shell systems, a level shift value of 0.5 to 3.0 is recommended. Start with a high value (2.0 - 3.0) for the first SCF calculation and then reduce it (to 0.5 - 1.0) for subsequent runs which use a converged SCF vector as the starting point.

It is extremely important to note that this version of the code no longer supports **OPENTYPE. One must use the new keywords REFERENCE and MULTP to specify the type of SCF needed.**

## INPUT FORMAT

The **cscf** program searches through the default keyword path (first **SCF** and then **DEFAULT**) for the following keywords:

**LABEL =***string*- This is a character string to be included in the output. This string is not used by the program. There is no default.
**WFN =***string*- This is the type of wavefunction which is ultimately desired. The default is
**SCF**. **OPENTYPE is no longer supported****REFERENCE =***string*- This specifies the type of SCF calculation one wants to do. It can be one of
**RHF**(for a closed shell singlet),**ROHF**(for a restricted open shell calculation),**UHF**(for an unrestricted open shell calculation),**TWOCON**(for a two configuration singlet), or**SPECIAL**. If**SPECIAL**is given, then alpha and beta coupling coefficients must be given with the**ALPHA**and**BETA**keywords. The default is**RHF**. **MULTP=***integer*- Specifies the multiplicity of the molecule. Default is singlet.
**CHARGE=***integer*- Specifies the charge of the molecule. Defauly is 0.
**DOCC =***integer_vector*- This gives the number of doubly occupied orbitals in each irreducible representation. There is no default. If this is not given, CSCF will attempt to guess at the occupations using the core hamiltonian.
**SOCC =***integer_vector*- This gives the number of singly occupied orbitals in each irreducible representation. There is no default.
**DERTYPE =***string*- This specifies the order of derivative that is to eventually be done. It is used by the
**scf**program to determine if certain files are to be written and it is also used to determine the default convergence of the wavefunction. The default is**FIRST**. **MAXITER =***integer*- This gives the maximum number of iterations. The default is 40.
**CONVERGENCE =***integer*- This specifies how tightly the wavefunction will be converged. Convergence is determined by comparing the RMS change in the density matrix ("delta P") to the given value. The convergence criterion is 10**(-
*integer*). The default is 7 if both**DERTYPE = NONE**and**WFN = SCF**are given and 10 otherwise. **LEVELSHIFT =***real*- This specifies the level shift. The default is 1.
**DIRECT =***boolean*- Specifies whether to do the SCF calculation with an integral direct technique. The default is false.
**PRINT_MOS =***boolean*- Specifies whether to print the molecular orbitals or not. The default is false.

There are also a large number of less commonly used input parameters. If you do not understand what the following options mean, then make sure that they do not appear in your input. The defaults will work in the overwhelming majority of cases. These are specified with the following keywords:

**DELETE_INTS =***boolean*- Integrals files will be erased if
**WFN = SCF**and**DERTYPE = FIRST**or**DERTYPE = NONE**. If you wish to keep integrals files then set**DELETE_INTS**= false. The default is true. **REORDER =***boolean*- The molecular orbitals will be reordered if this is true, in which case, the
**MOORDER**parameter must be present. The default is false. **MOORDER =***integer_vector*- This specifies a molecular orbital reordering vector. It will only be used if
**REORDER = YES**. This vector contains first the ordering for the orbitals in the first irreducible representation and then the second and so on. The first orbital of each irreducible representation is numbered 1. There is no default. **ALPHA =***real_vector*- If
**OPENTYPE = SPECIAL**, then this parameter gives the alpha coupling coefficients. The number of elements in this vector is MM(MM+1)/2, where MM is the number of irreducible representations containing singly occupied molecular orbitals. There is no default. **BETA =***real_vector*- If
**OPENTYPE = SPECIAL**, then this parameter gives the beta coupling coefficients. The number of elements in this vector is MM(MM+1)/2, where MM is the number of irreducible representations containing singly occupied molecular orbitals. There is no default. **GUESS =***string*- This option determines the type of initial guess at the eigenvector CSCF will use. The only valid option at the moment are : (1)
**GUESS = CORE**, which causes it to use core Hamiltonian eigenvector to start the calculation; (2)**GUESS = AUTO**which results in an attempt to use the MO vector in the checkpoint file, or resorts to core guess if there is no eigenvector in that file. The default if**AUTO**. **IPRINT =***integer*- This is a print option. The default is 0.
**MO_OUT =***boolean*- Prints out the orbitals with symmetry and occupations at the end of the calculation. Default is true.
**ROTATE =***boolean*- The molecular orbitals will not be rotated if this is false. The rotation only affects the virtual orbitals for open shell systems. This parameter must be true for correlated gradients and it must be false for second and higher derivatives. The default is false if
**WFN = SCF**and true otherwise. **CHECK_ROT =***boolean*- Check the molecular orbital rotation described above to ensure that no columns of the SCF eigenvector matrix are swapped by the rotation. Has no effect if
**ROTATE = false**. The default is true. **CHECK_MO_ORTHOGONALITY =***boolean*- Check if the molecular orbitals are orthonormal. Useful for debugging only. The default is false.
**DIIS =***boolean*- This determines whether diis will be used. The default is true.
**DIISSTART =***integer*- This gives the first iteration for which DIIS will be used. The default is 0.
**NDIIS =***integer*- This gives the number of error matrices to use in the diis procedure. The default is 6 for closed shell, 4 for open shell, and 3 for tcscf.
**DIISDAMP =***real*- This gives the damping factor for the diis procedure. The default is 0.0 for closed shell, 0.02 for open shell, and 0.01 for tcscf.
**INCR =***real*- This is used in tcscf to determine how often the ci coefficients are recalculated. A small number (~0.25) will cause them to be recalculated nearly every scf iteration. The default is 0.25.
**DYN_ACC =***boolean*- When performing direct scf this specifies whether dynamic integral accuracy cutoffs will be used. Default is true (use dynamic cutoffs). Initial iterations are performed with integrals accurate to six digits. After density is converged to 10^-5 or 30 iterations are completed, full integral accuracy is used. If scf convergence problems are experienced disabling dynamic cutoffs by setting this variable to false might help.
**ORTHOG_ONLY =***boolean*- Sometimes in CASSCF or other non-HF/KS schemes for orbital optimization, it is useful to reorthogonalize MO's from other geometries for the current geometry so they can be used as an initial guess for the new MO's. This can be performed by running CSCF with
**ORTHOG_ONLY = true**. After the orbitals are orthogonalized, the program will quit without performing an SCF computation. This keyword will be ignored if there are no previous orbitals in the checkpoint file. Defaults to**true**if**WFN = DETCAS**.

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