How do you explain easily "The spectrum of an electron in a repulsive potential " and hence "bound state of charge conjugation" in Dirac hole theory ?
Actually it will be better, if you write full sentence where you use this phrases.
"The spectrum of an electron in a repulsive potential" means that wavefunction of this electron describes impossibility for electron to occupy the same region of space where exists electron with the same spin. Hence "bound state of charge conjugation", that it can't be provide replacement of the particle into the corresponding antiparticle (eg, an electron into a positron). Probably, because of forces exists in this region of space.