Accurate ab initio methods are crucial for understanding chemical reactions on metal surfaces and calculating the thermodynamic stability of materials, especially in the case of metallic systems. One of the most widely used techniques for computing electronic correlation energies with systematically improvable accuracy is coupled-cluster theory. However, the well-known coupled cluster singles and doubles plus perturbative triples [CCSD(T)] approach, has limitations as it is only applicable to insulating materials. In the case of zero-gap materials, the truncation of the underlying many-body perturbation expansion results in an infrared catastrophe. To address this challenge, we introduce a novel perturbative triples formalism denoted as (cT), which provides convergent correlation energies in metallic systems. This newly proposed method not only overcomes the limitations of the existing CCSD(T) approach but also retains all the desirable properties of CCSD(T), including its accuracy for insulating systems and its computational efficiency compared to a full inclusion of triples. This paves the way for ab initio calculations of real metals with chemical accuracy.

[1] N. Masios, A. Irmler, T. Schaefer, A. Grueneis, Phys. Rev. Lett. (2023), preprint