  The electronic structures of SmX (X=N, P, As, Sb, Bi, O, S, Se, Te,
Po)compounds are calculated using the self-interaction corrected local-spin
density approximation. The Sm ion is described with either five or six
localized $f$-electrons while the remaining electrons form bands, and the total
energies of these scenarios are compared. With five localized $f$-electrons a
narrow $f$-band is formed in the vicinity of the Fermi level leading to an
effective intermediate valence. This scenario is the ground state of all the
pnictides as well as SmO. With six localized $f$-electrons, the chalcogenides
are semiconductors, which is the ground state of SmS, SmSe and SmTe. Under
compression the Sm chalcogenides undergo first order transitions with
destabilization of the $f$ states into the intermediate valence state, the
bonding properties of which are well reproduced by the present theory.
