The LCQS welcomed Paul Johnson as visiting Professor during the second week of September 2023.
Paul A. Johnson is an Associate Professor at the University of Laval in Québec. His research deals with strong electron correlation and seniority-zero wave functions. You can found more informations about him on his webpage.
He will give a seminar Tuesday, September 12, 2023 on ‘Strong Electronic Correlation with Richardson-Gaudin States‘
Abstract :
Weakly-correlated electronic systems are well-described as individual electrons: the wavefunction is a Slater determinant of the occupied orbitals with small corrections from single- and double-excitations. This is not the case for strongly-correlated systems. The wavefunction is very complicated in terms of Slater determinants and thus the correct physical picture is not independent electrons.
For strongly-correlated molecular systems, we have shown that the eigenvectors of reduced Bardeen-Cooper-Schrieffer Hamiltonians, so-called Richardson-Gaudin (RG) states, are a much better starting point. They describe weakly-correlated \emph{pairs} of electrons. They are tractable variationally and form a basis for the Hilbert space allowing for systematic improvement.
We will show for the isomers of H$_{10}$ that a single RG state is a very good approximation to the wavefunction. Corrections for the remaining weak electronic correlation are obtainable with an approximate functional, or with a short CI expansion in RG states. Thus, the present development is an analogue of both Kohn-Sham DFT and correlated wavefunction theories based on Slater determinant references.
