I used I-TASSER to predict the 3D structure of my protein of interest and PyMOL with APBS plugin to add a surface showing the electrostatic potential. Then, with PyTMs plugin, I added three phosphorylation sites to my original model and created another surface map. The two surface visualizations do not differ. How can I correctly visualize the electrostatic surface changes caused by the phosphorylation of selected amino acids?