On the properties of the Duffin-Kemmer-Petiau equation

In view of recent interest in the use of the Duffin-Kemmer-Petiau (DKP) relativistic equation, the authors consider some of its properties which are needed for practical calculations. They also address the unresolved problem of the spinless DKP boson in a central field and derive the system of first-order coupled differential radial equations which enable the energy eigenvalues as well as the full wavefunctions to be evaluated. As an example they calculate the free DKP spherical waves and then solve the problem of a pionic atom with a point Coulomb interaction only.