  The annihilation parameters of positrons with electrons in different shells
of Argon, Iron and Copper atoms are calculated below the positronium (Ps)
formation thresholds. Quite accurate ab initio calculations of the bound state
wavefunctions of Argon, Iron and Copper orbitals are obtained from Cowan
computer code. A least-squares variational method (LSVM) is used for
determining the wavefunction of the positrons. The program is employed for
calculating the s-wave partial cross sections of positrons scattered by Iron
and Copper atoms. Our results of the effective charge are compared with
available experimental and theoretical ones. --
