SciPost Chem. 1, 002 (2021) ·
published 18 May 2021

· pdf
A relativistic densityfunctional theory based on a Fockspace effective quantumelectrodynamics (QED) Hamiltonian using the Coulomb or CoulombBreit twoparticle interaction is developed. This effective QED theory properly includes the effects of vacuum polarization through the creation of electronpositron pairs but does not include explicitly the photon degrees of freedom. It is thus a more tractable alternative to full QED for atomic and molecular calculations. Using the constrainedsearch formalism, a KohnSham scheme is formulated in a quite similar way to nonrelativistic densityfunctional theory, and some exact properties of the involved density functionals are studied, namely chargeconjugation symmetry and uniform coordinate scaling. The usual nopair KohnSham scheme is obtained as a welldefined approximation to this relativistic densityfunctional theory.
Klaas Gunst, Dimitri Van Neck, Peter Andreas Limacher, Stijn De Baerdemacker
SciPost Chem. 1, 001 (2021) ·
published 15 January 2021

· pdf
We employ tensor network methods for the study of the seniority quantum number  defined as the number of unpaired electrons in a manybody wave function  in molecular systems. Seniorityzero methods recently emerged as promising candidates to treat strong static correlations in molecular systems, but are prone to deficiencies related to dynamical correlation and dispersion. We systematically resolve these deficiencies by increasing the allowed seniority number using tensor network methods. In particular, we investigate the number of unpaired electrons needed to correctly describe the binding of the neon and nitrogen dimer and the $D_{6h}$ symmetry of benzene.
SciPost Chem. 1, 002 (2021) ·
published 18 May 2021

· pdf
A relativistic densityfunctional theory based on a Fockspace effective quantumelectrodynamics (QED) Hamiltonian using the Coulomb or CoulombBreit twoparticle interaction is developed. This effective QED theory properly includes the effects of vacuum polarization through the creation of electronpositron pairs but does not include explicitly the photon degrees of freedom. It is thus a more tractable alternative to full QED for atomic and molecular calculations. Using the constrainedsearch formalism, a KohnSham scheme is formulated in a quite similar way to nonrelativistic densityfunctional theory, and some exact properties of the involved density functionals are studied, namely chargeconjugation symmetry and uniform coordinate scaling. The usual nopair KohnSham scheme is obtained as a welldefined approximation to this relativistic densityfunctional theory.
Klaas Gunst, Dimitri Van Neck, Peter Andreas Limacher, Stijn De Baerdemacker
SciPost Chem. 1, 001 (2021) ·
published 15 January 2021

· pdf
We employ tensor network methods for the study of the seniority quantum number  defined as the number of unpaired electrons in a manybody wave function  in molecular systems. Seniorityzero methods recently emerged as promising candidates to treat strong static correlations in molecular systems, but are prone to deficiencies related to dynamical correlation and dispersion. We systematically resolve these deficiencies by increasing the allowed seniority number using tensor network methods. In particular, we investigate the number of unpaired electrons needed to correctly describe the binding of the neon and nitrogen dimer and the $D_{6h}$ symmetry of benzene.