  We propose and develop the complex scaled multiconfigurational spin-tensor
electron propagator (CMCSTEP) technique for theoretical determination of
resonance parameters with electron-atom/molecule systems including open-shell
and highly correlated atoms and molecules. The multiconfigurational spin-tensor
electron propagator method (MCSTEP) developed and implemented by Yeager his
coworkers in real space gives very accurate and reliable ionization potentials
and attachment energies. The CMCSTEP method uses a complex scaled
multiconfigurational self-consistent field (CMCSCF) state as an initial state
along with a dilated Hamiltonian where all of the electronic coordinates are
scaled by a complex factor. CMCSCF was developed and applied successfully to
resonance problems earlier. We apply the CMCSTEP method to get $^2
P\,\mbox{Be}^{-}$ shape resonance parameters using $14s11p5d$, $14s14p2d$, and
$14s14p5d$ basis sets with a $2s2p3d$\,CAS. The obtained value of the resonance
parameters are compared to previous results. This is the first time CMCSTEP has
been developed and used for a resonance problem. It will be among the most
accurate and reliable techniques. Vertical ionization potentials and attachment
energies in real space are typically within $\pm 0.2\,eV$ or better of
excellent experiments and full configuration interaction calculations with a
good basis set. We expect the same sort of agreement in complex space.
