Taming Negative-Ion Resonances using Non-Local Exchange- Correlation Functionals

Characterization of negative ion resonances poses a fundamental challenge to density functional methods due to the unbound nature of resonances. We overcome this challenge by proposing one-particle non-local exchange-correlation (xc) potentials combining the exact-exchange (EXX) and the random phase approximation (RPA) correlation potentials. The negative ion resonances are identified by perturbing the real-Hermitian non-local xc potentials using complex absorbing local-potentials. Our studies show that the non-local EXX+RPA potential significantly enhances the description of positions and widths of negative ion resonance-states compared to potentials that include EXX only or include static polarization effects only. The use of low-scaling algorithms reduces the computational scaling of RPA potential thereby providing a practical solution to resonance-state characterization within the density functional framework. The theoretical framework and underlying assumptions required for combining real Hermitian non-local xc potentials with complex local potentials are discussed.