Gold-standard coupled-cluster accuracy for metals and small-gap solids
In plain words
The method chemists trust most for molecules, coupled cluster with perturbative triples (an approximate correction for three-electron correlations), gives an infinite correlation energy for metals. A version that works for metals with the same reliability is needed to benchmark surface chemistry and catalysis.
Precise statement
The perturbative triples correction (T) of CCSD(T) diverges for the uniform electron gas and for metals in the thermodynamic limit because of the long-range Coulomb interaction (infrared divergence). Determine whether a modified triples treatment (for example CCSD(cT), 2023) or full CCSDT gives cohesive energies, lattice constants and adsorption energies of simple and noble metals (Li, Na, Al, Cu) within 1 kcal/mol per atom of experiment or of numerically exact quantum Monte Carlo, with finite-size errors controlled. An answer is a convergent method demonstrated on these metals.
What would settle it
Thermodynamic-limit coupled-cluster calculations on metals and metal surfaces compared with quantum Monte Carlo and experimental cohesive and adsorption energies.
Status in the literature
In 2023 Masios, Irmler, Schafer and Gruneis (Phys. Rev. Lett., https://doi.org/10.1103/PhysRevLett.131.186401) showed that the CCSD(cT) variant removes the divergence in the uniform electron gas; tests on real metals and surfaces are limited.