Investigation of electron-atom/molecule scattering resonances using complex multiconfigurational self-consistent field method

We present a complex multicon figurational self-consistent field (CMCSCF)- based approach to investigate electron{atom/molecule scattering resonances. A modifi ed second quantization algebra adapted for biorthogonal spin orbitals has been applied to develop a quadratically convergent CMCSCF scheme. A new step-length control algorithm has been introduced in order to control the walk on the complex energy hypersurface and converge to correct CMCSCF stationary point. We have also developed a method (M1 method) based on the multiconfigurational spin tensor electron propagator (MCSTEP) to calculate resonance energies directly. These methods have been applied to investigate atomic and molecular scattering resonances. The test cases for our application were 2^P Be- and 2II_g N-_2 shape resonances. The position and the width of these resonances have been calculated for different complete active space choices. Convergence for CMCSCF calculations to a tolerance of 1:0 x 10^-10 a.u. for the energy gradient is achieved typically within ten iterations or less. The wide distribution of the values for the position and the width of the resonance reported in the literature has been explained by showing that there actually exists two distinct resonances which are close in energy. The resonance positions and widths from our calculation for the 2^IIg N-_2 shape resonance have been found to be very close to the experimental results. In another study, the effect of the orbitals with higher angular momentum has been investigated.