Format of the input.

Important: in the SlaterDeterminants calculations it is imperative that the results are obtained in the AOC field: no SCF convergence must be carried out, because we only want to assign the electrons differently, while keeping the AOC orbitals exactly as they are. To achieve this, the calculations should use the keyword SCF, and the subkey iterations has to be set to 0 in the SCF data block.

Since adf requires that the point-group symmetry conforms not only to the nuclear frame but also to the electronic charge density and mo occupations, these calculations must run in a lower pointgroup symmetry. Often you will also want to run the modified calculations spin-unrestricted.

For an example, see the set of sample runs that come with the package and the comments in the Examples document.

The calculation of the one-determinant states based on the AOC reference state is controlled with the key SLATERDETERMINANTS. It is a general key; it can be used as a simple key and requires an argument then. It can also be used as a block key. For this particular key it is not correct to specify an argument and a data block.

SLATERDETERMINANTS file

When used as a simple key, the argument must be a file (including the path). The file must be an ascii file containing data in the same format as you would supply in the data block when using the key as block type key, see below. All information on the file until the eof must be suitable for the data block, but no record 'end' on the file must be specified: only the contents of the data block.

The block format:

SLATERDETERMINANTS
   TITLE1
        irrep   occups
        irrep   occups
        ....
   SUBEND
   TITLE2
        irrep   occups
        ....
   SUBEND
   TITLE3
        irrep   occups
        ....
   SUBEND
   ....
END

Each 'title' functions as a subkey, but is otherwise an arbitrary string to label the resulting one-determinant calculation. Each such subkey block contains the occupation numbers for a single one-determinant calculation. It is necessary that the calculation uses the reference AOC run as its only fragment file. The occupations in the subkey blocks must be re-arrangements of the AOC open-shell electrons. In the SLATERDETERMINANTS calculation you must explicitly specify the pointgroup symmetry in which you want to run. The ρ^α and ρ^β densities of all determinants to be calculated must have this point group symmetry, or a higher symmetry.

Each 'irrep occups' record specifies the occupations for the indicated irrep in the usual way (see for instance the occupations key). The irrep labels must correspond to the AOC point group symmetry used in the AOC calculation, not the point group symmetry used in the SLATERDETERMINANTS calculation!. Note that in an unrestricted calculations, occupations numbers must be given for both spins, using the double slash (//) to separate the occupations for spin-alpha and spin-beta.

In this setup, the program will for each of the subkey blocks under the SLATERDETERMINANTS key execute an SCF calculation with only one cycle, i.e. no convergence, where the start-up field is the fragment field, i.e. the AOC field. So all one-determinant states in this calculation are evaluated in the AOC field. The resulting energies for the distinctly computed one-determinant states can then be combined to the desired multiplet values.