A method for accurate electron-atom resonances: The complex-scaled multiconfigurational spin-tensor electron propagator method for the ²P Be⁻ shape resonance problem

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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 PBe⁻ shape resonance parameters using 14s11p5d, 14s14p2d, and 14s14p5d basis sets with a 2s2p3dCAS. 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 ± 0.2eV 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.