The hydrogen atom as relativistic bound system

The hydrogen atom as relativistic bound-state system of a proton and an electron in the complex-mass scheme is investigated. Interaction of a proton and an electron in the atom is described by the Lorentz-scalar Coulomb potential; the proton structure is taken into account. The concept of position dependent particle mass is developed. Relativistic wave equation for two interacting spinless particles is derived; asymptotic method is used to solve the equation. % Asymptotic solution of the equation for the system in the form of %standing wave and eigenmasses of the $H$ atom are obtained. Complex eigenmasses for the $H$ atom are obtained. The spin center-of-gravity energy levels for the $H$ atom are calculated and compared with ones obtained from solution of some known relativistic wave equations % the Shr"odinger, Klein-Gordon and tabulated NIST data.