Analyze energy ranking from the optimized forcefield

[qzhu2017]

@mmukta

I just updated the script
https://github.com/MaterSim/pyocse/blob/main/compare_ranking.py

It will take the optimized 'parameters.xml' and 'references.xml' to plot the following

Try to

1. fix your references.xml
2. use pso to optimize the forcefield parameters with different strategies
3. Make the plots and get the rankings for those strategies
4. See if there is a way to improve the ff_ranking for the reference structure