University of Cambridge

摘要：

The mean-field solution to the electronic structure problem is given by the single Slater determinant produced by Hartree-Fock (HF) theory which, in many situations is a reasonably close approximation to the exact solution, lacking only dynamic correlation which can be provided by perturbative or other means. In so-called strongly correlated systems, where there are competing electronic structures, a single mean-field Slater determinant can represent only one of these, and perturbative treatments of correlation break down. The conventional solution to this problem would be a `multi-reference' method, such as Complete Active Space Self-Consistent Field theory, but such methods are far from black-box and generally scale poorly with system size.

We have shown that where there is strong correlation there are in fact many mean-field solutions[1] which act as quasidiabatic states and it is possible to combine them by a Non-Orthogonal Configuration Interaction (NOCI) approach[2] to recover a good description of the system. However, in the region between strong and weak correlation, these multiple solutions coalesce and disappear, making the method unsuitable in such regions. We show that by changing the form of Hartree-Fock to recover a complex-analytic, holomorphic, functional[3], wherever solutions coalesce, they analytically continue with complex coefficients. These holomorphic Hartree-Fock solutions are smooth and continuous, existing at all molecular geometries and so can be used as a basis for NOCI[4,5], recovering the strong correlation with little effort. We show that this approach is effective in some model electron transfer systems[6].

 [1] Locating multiple self-consistent field solutions: an approach inspired by metadynamics. AJW Thom, M Head-Gordon – Phys Rev Lett (2008) 101, 193001

[2] Hartree-Fock solutions as a quasidiabatic basis for nonorthogonal configuration interaction. AJW Thom, M Head-Gordon – The Journal of chemical physics 

(2009) 131, 124113

[3] Holomorphic Hartree-Fock Theory and Configuration Interaction. HG Hiscock,AJW Thom – Journal of chemical theory and computation (2014) 10, 4795

[4] Holomorphic Hartree-Fock Theory: An Inherently Multireference Approach

HGA Burton, AJW Thom – Journal of Chemical Theory and Computation (2016) 

12, 167

[5]Holomorphic Hartree-Fock Theory: The Nature of Two-Electron Problems.

HGA Burton, M Gross, AJW Thom – Journal of Chemical Theory and Computation 

(2018) 14, 607

[6]Modelling Electron Transfers Using Quasidiabatic Hartree-Fock States

KT Jensen, RL Benson, S Cardamone, AJW Thom – Journal of Chemical Theory and Computation (2018) 14, 4629

报告人简介: 

Alex Thom is a Royal Society University Research Fellow in the Department of Chemistry in the University of Cambridge. His research interests are in theoretical and computational chemistry, specializing in method development and software exploiting novel computer architectures. He has had positions in the University of California, Berkeley, and Imperial College London and is lead developer of the HANDE QMC package for stochastic quantum chemistry.