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**PROGRAM:**

**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**

**=**

__string__

The parameter controls reordering of molecular orbitals. If set to

**BEFORE**then the

guess orbitals from checkpoint file will be reordered. If set to

**AFTER**, converged

orbitals will be reordered before being written to the checkpoint file. In either

case

**MOORDER**parameter must be given to specify the reordering map. The default is

not to reorder orbitals.

**MOORDER**

**=**

__integer_vector__

This specifies a molecular orbital reordering vector. It will only be used if

**REORDER**is set. This vector maps every orbital to its new index, e.g.

**MOORDER**

**=**

**(0**

**2**

**1)**specifies that after reordering orbitals 1 and 2 will be swapped. The rank of

this vector is the same as the number of MOs. The indices are in Pitzer order

(ordered by symmetry, then by energy within each symmetry block), base-0. CSCF

will likely fail if the given MOORDER mixes orbitals from different irreps. 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**.

30 May, 1991 cscf(1)

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