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Self-consistent Green's function theory (GF2) significantly reduces fractional spin errors compared to MP2 theory. GF2 also maintains a small fractional charge error, improving upon MP2's limitations for strongly correlated systems.

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Electronic Structure Theory

Background:

  • Second-order Møller-Plesset perturbation theory (MP2) suffers from divergences for strongly correlated systems.
  • Self-consistent Green's function theory (GF2) is known to mitigate these issues, particularly reducing fractional spin errors.
  • The impact of GF2's Dyson equation summation on fractional charge error remains an open question.

Purpose of the Study:

  • To investigate the fractional charge and spin errors in self-consistent Green's function theory (GF2) within a second-order approximation.
  • To generalize GF2 implementation for open-shell systems to analyze these errors.
  • To compare GF2's performance against MP2 and common density functional approximations.

Main Methods:

  • Generalized implementation of second-order Green's function theory (GF2) for open-shell systems.
  • Analysis of fractional charge and spin errors arising from the self-consistent Dyson equation summation.
  • Comparative study with second-order Møller-Plesset (MP2) theory and hybrid density functionals.

Main Results:

  • GF2 demonstrates a greatly reduced fractional spin error compared to MP2, consistent with previous findings.
  • GF2 exhibits a very small fractional charge error, comparable to MP2.
  • GF2 shows lower fractional charge and spin errors than typical hybrid density functionals and random phase approximation with exchange.

Conclusions:

  • Self-consistent Green's function theory (GF2) effectively addresses MP2's shortcomings regarding strong correlations and fractional spin errors.
  • GF2 preserves the desirable low fractional charge error characteristic of MP2.
  • GF2 offers an improved theoretical framework over MP2 and common DFT methods for systems with strong correlation effects.