Purpose:
To define an initial set of molecular orbitals and to control use of super symmetry , frozen orbitals , deletion of orbitals , reordering and punching of orbitals.
, it is
generally recommended to use the new SUPSYM feature.
If you want to use ".AVERAGE
" the SUPSYM
feature must be disabled with ".NOSUPSYM
".
KAVER=1: double degeneracy, average KSYM(1) and KSYM(2)
KAVER=2: a) KSYM(1)=KSYM(3): triple degeneracy, average
KSYM(1), KSYM(2), KSYM(4)
b) else: two double degeneracies,
average KSYM(1) and KSYM(2), and
average KSYM(3) and KSYM(4).
KAVER .ne. 0 : MO coefficients are copied from the KSYM(1) and
KSYM(3) to the other degenerate symmetries to avoid
different orbitals through numerical roundoff errors.
READ (LUINP,*) (NNOR(ISYM), ISYM = 1,NSYM)
DO ISYM = 1,NSYM
IF (NNOR(ISYM) .GT. 0) THEN
READ (LUINP,*) (INOROT(I), I = 1,NNOR(ISYM))
...
END IF
END DO
where INOROT = orbital numbers of the orbitals to be
frozen
(not rotated) in symmetry "ISYM"
after any reordering (counting from 1 in each symmetry).
READ (LUINP,*) (NREOR(I), I = 1,NSYM)
DO I = 1,NSYM
IF (NREOR(I) .GT. 0) THEN
READ (LUINP,*) (IMONEW(J,I), IMOOLD(J,I), J = 1,NREOR(I))
END IF
END DO
NREOR(I) = number of orbitals to be reordered in symmetry I
IMONEW(J,I), IMOOLD(J,I) are orbital numbers in symmety I.
For example if orbitals 1 and 5 in symmetry 1 should change place, specify
.REORDER
2 0 0 0
1 5 5 1
Reordering of molecular orbitals (see comments).
Comments:
A new feature from 1992 is the automatic indentification of "super symmetry" , i.e. of irreps of the true point group of the molecule which is a "supergroup" of the Abelian group used in the calculation. Degenerate orbitals will be averaged and the "super symmetry" will be enforced in the orbitals. The use of "super symmetry" may be deactivated with the ".NOSUPSYM" keyword, for example in finite field calculations where the field lowers the symmetry.
For ABACUS and RESPONSE calculations, the "super symmetry" is deactivated unless explicitly enforced with .SUPSYM .
The initial orbitals must be symmetry orbitals, and the super symmetry analysis is performed on the kinetic energy matrix in this basis. The ".THRSSY" option is used to define when the kinetic energy matrix element between two orbitals is considered to be zero and when two diagonal matrix elements are degenerate. In the first case the orbitals can belong to different irreps of the supergroup and in the second case the two orbitals are considered to be degenerate. The analysis will fail if there are accidental degeneracies in diagonal elements. This can happen if the nuclear geometry deviates slightly from a higher symmetry point group, for example because too few digits has been used in the input of the nuclear geometry. If the program stops because the super symmetry analysis fails with a degeneracy error, you might consider to use more digits in the nuclear coordinates, to change THRSSY, or to disable super symmtry with ".NOSUPSYM". The value of THRSSY should be sufficiently small to avoid accidental degeneracies and sufficiently large to ignore small errors in geometry and numerical round-off errors.
REORDER MO can for instance be used for linear molecules to interchange undesired delta orbitals among the active orbitals in symmetry 1 with sigma orbitals. Another example is movement of the core orbital to the RAS1 space for core hole calculation. In general use of this option necessitates a pre-calculation with STOP AFTER MO-ORTHONORMALIZATION and identification of the various orbitals by inspection of the output.