  Existence of ferromagnetism in bulk calcium compounds is discovered
theoretically. First-principles calculations of calcium phosphide, calcium
arsenide and calcium antimonide in the zinc-blende structure have been
performed to show the half-metallic ground state in each optimized stable
structure. Magnetism comes from spin-polarization of electrons in
  $p$-orbitals of P, As or Sb and $d$-orbitals of calcium atoms. The
half-metallicity is analogous to the half-metallic zinc-blende compounds, {\it
e.g.} CrAs or CrSb, but the predicted compounds become ferromagnetic without
transition metals. In (In$_{1-x}$Ca$_x$)Sb, the magnetism remains to be stable
in a range of the doping rate ($x>0.8$).
