39 citations · 283 across the 20 of their papers we have counts for
16 papers · 1 filter
Excited states, symmetry breaking, and unphysical solutions in state-specific CASSCF theory
Antoine Marie, Hugh G. A. Burton
State-specific electronic structure theory provides a route towards balanced excited-state wave functions by exploiting higher-energy stationary points of the electronic energy. Mu…
Convergence of Møller-Plesset perturbation theory for excited reference states
Diana-Gabriela Oprea, Hugh G. A. Burton
Excited states in molecules can be difficult to investigate and generally require methods that are either computationally expensive or are not universally accurate. Recent research…
Generalized nonorthogonal matrix elements for arbitrary excitations
Hugh G. A. Burton
Electronic structure methods that exploit nonorthogonal Slater determinants face the challenge of efficiently computing nonorthogonal matrix elements. In a recent publication, H. G…
Complex analysis of divergent perturbation theory at finite temperature
Yi Sun, Hugh G. A. Burton
We investigate the convergence properties of finite-temperature perturbation theory by considering the mathematical structure of thermodynamic potentials using complex analysis. We…
Energy Landscape of State-Specific Electronic Structure Theory
Hugh G. A. Burton
State-specific approximations can provide an accurate representation of challenging electronic excitations by enabling relaxation of the electron density. While state-specific wave…
Variations of the Hartree-Fock fractional-spin error for one electron
Hugh G. A. Burton, Clotilde Marut, Timothy J. Daas +2
Fractional-spin errors are inherent in all current approximate density functionals, including Hartree-Fock theory, and their origin has been related to strong static correlation ef…
Hartree-Fock Critical Nuclear Charge in Two-Electron Atoms
Hugh G. A. Burton
Electron correlation effects play a key role in stabilising two-electron atoms near the critical nuclear charge, representing the smallest charge required to bind two electrons. Ho…
Generalised Nonorthogonal Matrix Elements: Unifying Wick's Theorem and the Slater-Condon Rules
Hugh G. A. Burton
Matrix elements between nonorthogonal Slater determinants represent an essential component of many emerging electronic structure methods. However, evaluating nonorthogonal matrix e…
Perturbation Theory in the Complex Plane: Exceptional Points and Where to Find Them
Antoine Marie, Hugh G. A. Burton, Pierre-François Loos
We explore the non-Hermitian extension of quantum chemistry in the complex plane and its link with perturbation theory. We observe that the physics of a quantum system is intimatel…
Holomorphic Density Functional Theory
Rhiannon A. Zarotiadis, Hugh G. A. Burton, Alex J. W. Thom
Self-consistent-field (SCF) approximations formulated using Hartree-Fock (HF) or Kohn-Sham Density Functional Theory (KS-DFT) both have the potential to yield multiple solutions. H…
Reaching Full Correlation through Nonorthogonal Configuration Interaction: A Second-Order Perturbative Approach
Hugh G. A. Burton, Alex J. W. Thom
Nonorthogonal multireference methods can predict statically correlated adiabatic energies while providing chemical insight through the combination of diabatic reference states. How…
A General Approach for Multireference Ground and Excited States using Non-Orthogonal Configuration Interaction
Hugh G. A. Burton, Alex J. W. Thom
A balanced description of ground and excited states is essential for the description of many chemical processes. However, few methods can handle cases where static correlation is p…
-Symmetry in Hartree-Fock Theory
Hugh G. A. Burton, Alex J. W. Thom, Pierre-François Loos
-symmetry --- invariance with respect to combined space reflection and time reversal --- provides a weaker condition than (Dirac) Hermitic…
Complex Adiabatic Connection: a Hidden Non-Hermitian Path from Ground to Excited States
Hugh G. A. Burton, Alex J. W. Thom, Pierre-François Loos
Processes related to electronically excited states are central in many areas of science, however accurately determining excited-state energies remains a major challenge in theoreti…
Holomorphic Hartree-Fock Theory: The Nature of Two-Electron Problems
Hugh G. A. Burton, Mark Gross, Alex J. W. Thom
We explore the existence and behaviour of holomorphic restricted Hartree-Fock (h-RHF) solutions for two-electron problems. Through algebraic geometry, the exact number of solutions…
Holomorphic Hartree-Fock theory: an inherently multireference approach
Hugh G. A. Burton, Alex J. W. Thom
We investigate the existence of holomorphic Hartree-Fock solutions using a revised SCF algorithm. We use this algorithm to study the Hartree-Fock solutions for H and H$_{4}^{…