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Interpolated Partition Function

To generate partition functions from an externally provided table of values (such as those provided by HITRAN) add an "InterpolatedPartitionFunction" object at the molecule level. Provided the active property is set then, when requiring partition functions, PGOPHER will interpolate from the provided table, rather than attempting a sum over all calculated levels. Unless several ground state vibrational levels are included in the calculation, this approach is likely to be necessary for full accuracy in absolute intensities. To load the table, right click on the object in the tree view and select "Import..."; a simple text file is expected with at least two values on each line, the temperature (K) and the corresponding value of the partition function (More columns can be present.) On loading the file you will normally be prompted to select the columns containing the temperature (T) and partition function values, Q. After loading, the values will be visible as extra parameters, and can be edited as with other values.

With this set up and active, the populations are taken as:

g/(Scale×Qext) exp( -(E-Emin-Ezero) / kBT )

where Qext is the interpolated value derived from the values given. Emin is used if the AutoZero flag is on, and is the lowest calculates energy, and has the effect of shifting the energy origin of the calculated levels to zero. (The origin is otherwise dependent on how the data file is set up and the choice of the Hamiltonian.) Ezero is the origin used when the external partition function was calculated.


Active If true, use this to generate the partition function
Order Order of Lagrangian interpolation to use. The default is 4, as used by HITRAN
AutoZero If true, Emin in the formula above is the lowest calculated energy. If false it is taken as zero.
Multiply Partition function is taken as Q = Qcalc× Qext rather than simply Qext. If only one vibronic stae is included in the main calculation, this is equivalent to providing the vibronic partition function.

Versions before 8.0.217 had Fractional instead of Multiply, and used Qcalc× Qext. Old data files are automatically converted on loading by taking the reciprocal of the values for Qext.


Zero Energy zero of the external partition function.
Scale Scale interpolated partition function by this
If T and Q values have been loaded, these will be visible below these parameters.