Molecule Types Symmetric Tops <Prev Next>

Symmetric Top Molecule

These are the settings for a symmetric molecule as a whole, i.e. those common to all states (but perhaps different for different isotopologues).


nNuclei Number of nuclei to calculate hyperfine structure for. Leave this at 0 unless you want the hyperfine structure resolved.
Jmin Minimum J to use in calculation - set to -1 (default) to use value from species.
Jmax Maximum J to use in calculation - set to -1 (default) to use value from species.
Colour Colour - set to "None" to take value from elsewhere as explained in Determining Colours and J ranges.
JAdjustSym If set, 1 and 2 in irreducible representations are replaced by + and - for even J and - and + for odd J in A and B irreducible representations. This takes account of the alternation in symmetry with J that is often found. Note that this was only fully implemented in version 8.0.285.
BlockMatrix Set to force check of Hamiltonian matrix for factorization into blocks before diagonalization. If blocks are found, these are diagonalized separately, ensuring states that have no connecting matrix elements are not accidentally mixed if the eigenvalues happen to be very close. In principle, if full use is made of symmetry and states are separated into separate manifolds as appropriate, this should not be necessary but can easily happen if selected terms in the Hamiltonian are zero or interactions between states are omitted.
AbsoluteE True if energies have not been offset. This is not the default for compatibility with previous versions, though perhaps should be for new calculations. Setting this false (the default) allows transitions with negative frequencies, which can occasionally be convenient for simulations involving a small spread of frequencies around a large central frequency where a large offset is applied to the upper state origin. This can give erroneous negative frequencies; while there is logic to detect common cases where this might arise, some calculations (typically involving near degenerate manifolds) require this to be set to true for correct operation.
PointGroup Point group of molecule. Possible values are:
C3v, C4v, C5v, C6v, C7v, C8v, D3h, D4h, D5h, D6h, D7h, D8h, D2d, D3d, D4d, D5d, D6d, D7d, D8d.
The separably degenerate groups C3h,C4h, C5h, C6h, S4, S6, S8, S10, S12, D3, D4, D5, D6, D7, D8 are also partially implemented.
AlternateBasis Set to use and alternate basis in separably degenerate point groups, with |K,l> and |-K,-l> for non E symmetry functions, rather than {|K,l> ± |-K,-l>}
Controls when rovibronic symmetry labels are used on transition labels, and state labels if CompactKLabels is true. Possible values are:
  • Always - The rovibronic symmetry is always shown
  • Required - The default. The rovibronic symmetry is only shown when it cannot be determined simply from K and l. This is normally for K ≠ 0 levels that are not of degenerate (E) rovibronic symmetry. For example, non degenerate vibronic states in C3v show pairs of levels when K is a multiple of 3 with A1 and A2 symmetry. These levels are not formally degenerate (as they have different symmetry) but the splitting between then is typically not resolvable in most spectra.
  • Never - The rovibronic symmetry is never given. Note that this may result in two different states or transitions having the same set of quantum numbers, but may well be adequate in simple cases.
CompactKLabels State labels combine the K, l and rovibronic labels into a single item. This gives a format equivalent to the simple quantum number format for symmetric tops, as described in line list input format. Note that this flag affects the line list format where an indexoffsets search or indexoffsets searchall directive is used.
Statistical Weights for each rovibronic symmetry. The number of settings here depends on the point group set as above, with one setting per set of rovibronic symmetries that have the same associated nuclear spin functions.


Abundance Abundance of this isotope; default is 1
AssumedOrigin Can normally be left at the default value; see the generic Molecule entry for more information