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Constrained Random Phase Approximation: the spectral method
Merzuk Kaltak, Alexander Hampel, Martin Schlipf, Indukuru Ramesh Reddy, Bongae Kim, Georg Kresse
https://arxiv.org/abs/2508.15368

Constrained Random Phase Approximation: the spectral method
We present a new constrained Random Phase Approximation (cRPA) method, termed spectral cRPA (s-cRPA), and compare it to established cRPA approaches for Scandium and Copper by varying the 3d shell filling. The s-cRPA consistently yields larger Hubbard $U$ interaction values. Applied to the realistic system CaFeO$_3$, s-cRPA produces interaction parameters significantly closer to those required within DFT+$U$ to induce the experimentally observed insulating state, overcoming the metallic behavior…