Determination of superfine splitting of positronium energy levels

Energies of the singlet and triplet positronium states are analytically calculated considering the annihilation and loop corrections in a functional approach. The dependences of the constituent mass of constituent particles on the initial-state masses and the corresponding quantum number are derived. The wave function at the origin of coordinates is calculated and the decay widths of ortho- and parapositronium are determined. The result corresponds satisfactorily to available experimental data.