Hilbert space multireference coupled cluster tailored by matrix product states.

0580139 - ÚFCH JH 2024 RIV US eng J - Journal Article
Demel, Ondřej - Brandejs, Jan - Lang, Jakub - Brabec, Jiří - Veis, Libor - Legeza, Ö. - Pittner, Jiří
Hilbert space multireference coupled cluster tailored by matrix product states.
Journal of Chemical Physics. Roč. 159, č. 22 (2023), č. článku 224115. ISSN 0021-9606. E-ISSN 1089-7690
R&D Projects: GA ČR(CZ) GA18-24563S; GA ČR(CZ) GA19-01897S
Research Infrastructure: e-INFRA CZ II - 90254; e-INFRA CZ - 90140
Institutional support: RVO:61388955
Keywords : HOMO and LUMO * Hilbert-space multi-reference coupled-cluster method * Coupled-cluster methods
OECD category: Physical chemistry
Impact factor: 4.4, year: 2022
Method of publishing: Open access

In the past decade, the quantum chemical version of the density matrix renormalization group method has established itself as the method of choice for strongly correlated molecular systems. However, despite its favorable scaling, in practice, it is not suitable for computations of dynamic correlation. Several approaches to include that in post-DMRG methods exist, in our group, we focused on the tailored coupled cluster (TCC) approach. This method works well in many situations. However, in exactly degenerate cases (with two or more determinants of equal weight), it exhibits a bias toward the reference determinant representing the Fermi vacuum. Although sometimes it is possible to use a compensation scheme to avoid this bias for energy differences, it is certainly a drawback. In order to overcome this bias of the TCC method, we have developed a Hilbert-space multireference version of tailored CC, which can treat several determinants on an equal footing. We have implemented and compared the performance of three Hilbert-space multireference coupled cluster (MRCC) variants-the state universal one and the Brillouin-Wigner and Mukherjee's state specific ones. We have assessed these approaches on the cyclobutadiene and tetramethyleneethane molecules, which are both diradicals with exactly degenerate determinants at a certain geometry. We have also investigated the sensitivity of the results on the orbital rotation of the highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) pair, as it is well known that Hilbert-space MRCC methods are not invariant to such transformations.
Permanent Link: https://hdl.handle.net/11104/0348905