Unphysical discontinuities, intruder states and regularization in GW methods

By recasting the non-linear frequency-dependent GW quasiparticle equation into a linear eigenvalue problem, we explain the appearance of multiple solutions and unphysical discontinuities in various physical quantities computed within the GW approximation. Considering the GW self-energy as an effective Hamiltonian, it is shown that these issues are key signatures of strong correlation in the (N +/- 1)-electron states and can be directly related to the intruder state problem. A simple and efficient regularization procedure inspired by the similarity renormalization group is proposed to avoid such issues and speed up the convergence of partially self-consistent GW calculations. Published under an exclusive license by AIP Publishing.

Automated summary

By recasting the non-linear frequency-dependent GW quasiparticle equation into a linear eigenvalue problem, this study explains the occurrence of multiple solutions and unphysical discontinuities in various physical quantities computed within the GW approximation. The GW self-energy is treated as an effective Hamiltonian, which reveals the key signatures of strong correlation in the (N +/- 1)-electron states and their direct relation to the intruder state problem. A regularization procedure inspired by the similarity renormalization group is proposed to avoid these issues and accelerate the convergence of partially self-consistent GW calculations.