Recorded 29 March 2022. Reinhold Schneider of Technische Universität Berlin, Institut für Mathematik, FG Modellierung, Simulation & Optimieru presents "Tensor Networks (QC-DMRG) in a Complete Active Space Coupled Cluster Method" at IPAM's Multiscale Approaches in Quantum Mechanics Workshop. Abstract: In the framework of tree based tensor networks (HT/TT tensor) the Schrdinger equation is formulated in second quantization in a discrete Fock space, and usually solved by alternating search algorithms like DMRG (density matrix renormalization group). This provides high quality approximation of the full CI solution even in presence of strong correlation phenomena. Although the approach using Matrix Product States (MPS-TT tensors) has been successfully applied for computing systems in a s strong correlation regime, it remains to be too expensive for computing dynamical correlations. Therefore we combine this approach (e.g. MPS-DMRG) in a MR-SCF-CAS (multi-reference complete active space) with the tailored multi-reference coupled cluster (MRCC) ansatz. The latter accounts for the dynamical correlation not captured by DMRG. The cost of tailored MR-CC calculation remains similar to that for standard single double coupled cluster calculations, but strong correlation effects, degenerate and nearly degenerate states can be computed as well. The convergence analysis is based on earlier analysis of the Coupled Cluster approximation and on joint work with F. Faulstich (TUB), O. Legeza (Budapest) A. Laestadius and S. Kvaal (Dept. Chemistry U Oslo). Learn more online at: http://www.ipam.ucla.edu/programs/workshops/workshop-i-multiscale-approaches-in-quantum-mechanics/?tab=schedule