How to draw dimer charge transfer graph


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I will be great if any one can help me how to draw the dimer charge transfer graph. From tutorial i have understand how to do charge transfer calculations. But i am unable to draw the graph similar to graph shown in below link :
http://nwchemgit.github.io/index.php/File:RT_TDDFT_tcne_td_charge.png [1]


Regards,
Chaitanya