CaDS Seminar 2024 - Jan. 16

Dr. Thomas Müller (SDL Complex Particle Systems)

Matrix rank reduction schemes for multi-reference methods

Abstract:

Widely applied single-reference methods such as Coupled Cluster, Moeller-Plesset Perturbation theory and Hartree-Fock (HF) tend to fail for ground state non-equilibrium geometries. Density Functional Theory (DFT) is both for electronic ground and excited states more robust but gives rise to considerable, unpredictable and unsystematic errors for strongly correlated systems. The latter are characterized by closely spaced electronic states and multi-reference nature even of the ground state.

Multi-reference methods provide access to high-level ab-initio data on such molecular structures. Yet, their application is rather limited owing to their high computational cost as well as ressource requirements. In particular DFT and HF have benefitted over the last three decades from rank reduction schemes that greatly reduced both ressource consumption and computational effort.

The Multi-configurational self consistent field (MCSCF) method is the first step in any multireference treatment and also central to the ressource reduction in the subsequent steps. After a brief introduction to the role of tensor contraction in Quantum Chemistry, a new version of a general MCSCF code with substantially reduced ressource requirements also due to matrix rank reduction schemes is discussed.