Making a basic data file for simulating vibrational structure
A simple vibrational structure data
file can be generated from File, New,
Vibrational Structure. This sets up the program to simulate
an electronic transition with an origin as 50000 cm-1
and one active vibration with a ground state frequency, ω", = 1000
cm-1 reducing to 750 cm-1 in the excited
state and displaced by 0.5 along the normal co-ordinate. To adjust
the constants, add more modes or change the type of vibronic
transition use View,
Constants. Most constants and settings can be left unchanged
at their default values (and indeed should be unless you need a
specific effect) but the ones that must normally be changed are
adjusted as follows:
- To set the number of vibrational modes and symmetry of the
molecule click on "VibratingMolecule"
and change "nModes"
and "PointGroup" as
required. You need only enter the number of modes that you are
interested in. Note that you should leave "nNuclei" at 0 unless
you specifically want to calculate Franck-Condon factors from
the l matrix - see Making a data file for simulating
vibrational structure from the l matrix
- The symmetry of the ground electronic state is set by clicking
on "X" and altering "Symmetry"
as required. (The default is totally symmetric.)
- To enter the ground state vibrations click on "v1", "v2" ... in turn under "X" - if the number that
appear is wrong set "nModes"
as in step 1. The key things to set are the vibrational
the symmetry of the vibrational mode, "Symmetry" and "vMax", the maximum
value of the vibrational quantum number to consider in each
The symmetry and origin of the excited electronic state is set
by clicking on "A"
and altering "Symmetry"
The excited state vibrational frequencies are then entered by
clicking on "v1", "v2" ... in turn under "A", and setting "Omega" as required.
Finally the displacements along each normal mode (K) between the two
electronic states are entered by clicking on the individual
modes under <A|FCF|X> and setting "Displacement"
Other things to adjust are the anharmonicities "xOmega", "yOmega", "zOmega" and the mode mixing
(the additional values under displacement).
- Setting the symmetry of a mode in one state will alter the
same mode in all other electronic states of the molecule, so
you do not need to change the symmetries of the vibrations in
the excited state.
- To avoid a very large calculation, only set vMax
non-zero for a few modes; if the product over all modes of
(vMax+1) is more than 50 or so the calculation is likely to
become rather slow.