Polfit

This will fit a polynomial to the potential energy of a diatomic as a function of separation, then perform a simple Dunham analysis on it.

Dependencies

• Python 3.5 or higher
• Numpy
• texttable
• matplotlib

Running the script

The input is simply a tab-delimited text file of data, which must include a header row with column names. See for example cl2test.dat.

The script is then run as (assuming coordinates are in BOHR):

python3 polfit.py -f [input file] -mu [reduced mass of diatomic in atomic mass units]

If your coordinates are in ANGSTROM instead, pass the flag

-angstrom True

If you want to plot one or more of the polynomial fits, pass

-plot [list of col. numbers]

Finally, you can change the order of polynomial fitted with

-order [order of poly]

Note that this must be >= 6 for the anharmonicity constants to be calculated.

e.g. for the cl2test.dat example (which is in Angstrom):

python3 polfit.py -f cl2test.dat -mu 17.7265 -angstrom True

would give the usual analysis as per MOLPRO, while:

python3 polfit.py -f cl2test.dat -mu 17.7265 -angstrom True -plot 1 2 -order 5

would do the analysis with a 5th-order polynomial, and plot both the EHF and ECC (columns 1 and 2 of the input). Changing the plot flag to -plot 2 would just plot the ECC fit.