Electron magnetic moment
https://en.wikipedia.org/wiki/Electron_magnetic_moment
https://physics.stackexchange.com/questions/30955/magnetic-moment-derivation-from-dirac-equation
https://www.rpi.edu/dept/phys/Courses/PHYS6520/DiracElectron.pdf
http://www.pas.rochester.edu/~passage/resources/prelim/Quantum/UCB%20Notes/45%20dirac.pdf