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Welcome to CC-aims

What is CC-aims

CC-aims is an interface between the "Fritz Haber Institute ab-initio molecular simulations" (FHI-aims) package and the "Coupled cluster for solids" (CC4S) code by the group of Andreas Grüneis. The input of CC4S consists of

  • data files - They contain ab-initio quantities including HF/KS eigenenergies, the Fock matrix etc.
  • yaml files - They specify the shape and sparsity of these quantities.

All the quantities contained in the data files are either parsed or calculated and corresponding yaml files are generated by CC-aims, so that subsequent calculations via CC4S can be performed right away.

In addition, CC-aims can be seen as a generalizable template for other ab-initio software packages, which use localized atomic basis sets, to implement analogues interfaces to CC4S, which takes specifics of the respective codes into consideration.

An interface to CC4S, like CC-aims, grants the interfacing code access to a continuously growing range of highly optimized beyond-DFT quantum chemistry methods, including perturbation theory (MP2) and Coupled Cluster theory (CC). As the name of CC4S suggests, all therein implemented algorithms can work with both periodic and molecular systems.

Prerequisites for ab-initio codes

Codes, other than FHI-aims, which intend to use the CC-aims interface, need to fulfill 2 fundamental criteria to do so. An interfacing ab-initio code must:

  • use a localized atomic basis set (GTOs, STOs, NAOs etc.)
  • use a resolution-of-identity (RI) formalism e.g for the representation of Coulomb integrals. CC-aims can deal with both local RI schemes (e.g RI-LVL) and non-local ones (most commonly RI-V and RI-SVS etc.)

User or developers of codes, which do not comply with the first prerequiste, and for example employ a plain-wave basis, should have a look at the paper by the Grüneis group here. There the equations for the construction of the Coulomb vertex in a plain-wave basis are presented.