Tackling strong correlation: Spin-flip method and its applications to single molecular magnets

DIPC Seminars

Anna I. Krylov, University of Southern California
Donostia International Physics Center
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Tackling strong correlation: Spin-flip method and its applications to single molecular magnets Strong correlation, which emerges due to electronic near-degeneracies such as small HOMO-LUMO gaps, is notoriously difficult to describe by electronic structure methods. Spin-flip (SF) family of methods offers a practical solution to this problem by utilizing a well-behaved high-spin reference state, which can be well described by a single Slater determinant, and treating multi-configurational low-spin states as excited states involving spin-flip. SF ansatz can be combined with a variety of ab initio methods, ranging from configuration interaction and coupled-cluster methods to Kohn- Sham density functional theory. It has been used to model electronic structure of di- and tr-radicals, singlet fission systems, as well as single-molecule magnets (SMMs). This lecture will describe the SF approach and illustrate its utility by using di- and tri-nuclear copper SMMs, which are of potential interest for quantum information science. 1\. A.I. Krylov, The Spin-Flip Equation-of-Motion Coupled-Cluster Electronic Structure Method for a Description of Excited States, Bond-Breaking, Diradicals, and Triradicals, Acc. Chem. Res. 39 83-91 (2006). 
 2\. Y.A. Bernard, Y. Shao, and A.I. Krylov, General Formulation of Spin-Flip Time Dependent Density Functional Theory Using Non-Collinear Kernels: Theory, Implementation, and Benchmarks, J. Chem. Phys. 136 204103 (2012). 
 3\. N. Orms and A.I. Krylov, Singlet-Triplet Energy Gaps and the Degree of Diradical Character in Binuclear Copper Molecular Magnets Characterized by Spin-Flip Density Functional Theory, Phys. Chem. Chem. Phys. 20 13095-13662 (2018). 
 4\. N.J. Mayhall and M. Head-Gordon, Computational quantum chemistry for multiple-site Heisenberg spin couplings made simple: Still only one spin-flip required, J. Phys. Chem. Lett. 6, 1982 (2015). Host: David Casanova