A Systematic Convergent Sequence of Approximations (of Integral Equation Form) to the Solutions of the Hedin Equations
This paper introduces a systematic series of integral equation-based approximations (Hedin I, II, III, etc.) that converge to the exact Hedin equations, offering a numerically tractable method to improve upon the GW approximation and capture increasingly complex Feynman diagrams, as demonstrated through zero-dimensional field theory.