Molecular Physics seminar

Localized orbitals, strong correlation and coupled cluster theory

by Susi Lehtola (Lawrence Berkeley National Laboratory, Berkeley CA, USA)

C6:3072 ()


I will start by discussing various orbital localization schemes, and present some results with an approach we have recently developed [1] to generate maximally localized Wannier functions that preserve sigma-pi orbital separation without the need for any special considerations [2]. In the latter part of the talk I will discuss the treatment of systems with strong correlation using coupled-cluster theory, especially focusing on the perfect pairing hierarchy of methods that are essentially based on a localized orbital description; the perfect pairing hierarchy of methods [3]. These are extremely cost-efficient approximations to the complete active space self-consistent field (CAS-SCF) method that are routinely able to treat problems of unforeseen sizes: several hundred electrons in several hundred orbitals on a single workstation. We have recently finished the implementation of orbital optimisation for the methods, applications of the methods will be presented for polyacenes in the full valence space up to 12acene (238e,238o). [1] S. Lehtola and H. Jónsson, J. Chem. Theory Comput. 10, 642 (2014). DOI: 10.1021/ct401016x [2] E. Ö. Jónsson, S. Lehtola, M. Puska, and H. Jónsson, J. Chem. Theory Comput. 13, 460 (2017). DOI: 10.1021/acs.jctc.6b00809. [3] S. Lehtola, J. Parkhill, and M. Head-Gordon, J. Chem. Phys. 145, 134110 (2016). DOI: 10.1063/1.4964317.