2025/01/22 by Alexander Waigum, Sarah Suchaneck, Andreas Köhn · 1 voice
Engineering · Physics and Astronomy · #Advanced Chemical Physics Studies #Perovskite Materials and Applications #Spectroscopy and Quantum Chemical Studies
paper · pdf · doi:10.1002/jcc.70020
openalex publication_date 2025/01/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/05/21
ABSTRACT We define an approximation to the internally contracted multireference coupled‐cluster method with single and double excitations by a hybrid approach. The rationale is to treat the external pair energy contributions by the coupled‐cluster method, which provides accurate results for a large part of the correlation energy while being tractable as the involved pair cluster operators commute. For the internal and semi‐internal contributions, for which the coupled‐cluster part becomes involved due to non‐commuting operators, a linearized approach based on the coupled‐electron pair approximation (CEPA) is used. For the latter, the CEPA(0) method, the averaged coupled pair functional (ACPF), the averaged quadratic coupled‐cluster (AQCC) method, and the averaged CEPA method are tested. We test the methods concerning size consistency, potential energy curves for C 2 , N 2 , CN, and O 3 and for the singlet‐triplet splitting of ortho‐, meta‐, and para‐benzynes. Our results show that AQCC provides the most accurate results and stable performance. The main drawback of the method is that it shows small violations of size consistency.