We investigate static correlation and delocalization errors in the self-consistent GW and random-phase approximation (RPA) by studying molecular dissociation of the H2 and LiH molecules. Although both approximations contain topologically identical diagrams, the nonlocality and frequency dependence of the GW self-energy crucially influence the different energy contributions to the total energy as compared to the use of a static local potential in the RPA. The latter leads to significantly larger correlation energies, which allow for a better description of static correlation at intermediate bond distances. The substantial error found in GW is further analyzed by comparing spin-restricted and spin-unrestricted calculations. At large but finite nuclear separation, their difference gives an estimate of the so-called fractional spin error normally determined only in the dissociation limit. Furthermore, a calculation of the dipole moment of the LiH molecule at dissociation reveals a large delocalization error in GW making the fractional charge error comparable to the RPA. The analyses are supplemented by explicit formulas for the GW Green's function and total energy of a simplified two-level model providing additional insights into the dissociation limit.
- static correlation
Hellgren, M., Caruso, F., Rohr, D. R., Ren, X., Rubio, A., Scheffler, M., & Rinke, P. (2015). Static correlation and electron localization in molecular dimers from the self-consistent RPA and GW approximation. Physical Review B, 91(16), 1-12. . https://doi.org/10.1103/PhysRevB.91.165110