Now showing items 1-11 of 11

  • Bodenstein, Tilmann; Kvaal, Simen (Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2020)
    A state-specific multireference coupled-cluster (MRCC) method based on Arponen’s bivariational principle is presented, the bivar-MRCC method. The method is based on single-reference theory and therefore has a relatively ...
  • Laestadius, Andre; Kvaal, Simen (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2018)
    The mathematical foundation of the so-called extended coupled-cluster method for the solution of the many-fermion Schrödinger equation is here developed. We prove an existence and uniqueness result, both in the full ...
  • Faulstich, Fabian Maximilian; Laestadius, Andre; Legeza, Örs; Schneider, Reinhold; Kvaal, Simen (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2019)
    n quantum chemistry, one of the most important challenges is the static correlation problem when solving the electronic Schrödinger equation for molecules in the Born--Oppenheimer approximation. In this article, we analyze ...
  • Tellgren, Erik; Kvaal, Simen; Sagvolden, Espen; Ekström, Ulf Egil; Teale, Andrew Michael; Helgaker, Trygve (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2012)
    The selection of basic variables in current-density-functional theory and formal properties of the resulting formulations are critically examined. Focus is placed on the extent to which the Hohenberg-Kohn theorem, ...
  • Jarlebring, Elias; Kvaal, Simen; Michiels, Wim (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2011)
    Double eigenvalues are not generic for matrices without any particular structure. A matrix depending linearly on a scalar parameter, Α + μΒ, will, however, generically have double eigenvalues for some values of the parameter ...
  • Tellgren, Erik; Kvaal, Simen; Helgaker, Trygve (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2014)
    The N-representability problem is the problem of determining whether there exists N-particle states with some prescribed property. Here we report an affirmative solution to the fermion N-representability problem when both ...
  • Laestadius, Andre; Penz, Markus; Tellgren, Erik; Ruggenthaler, Michael; Kvaal, Simen; Helgaker, Trygve (Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2018)
    A detailed account of the Kohn–Sham (KS) algorithm from quantum chemistry, formulated rigorously in the very general setting of convex analysis on Banach spaces, is given here. Starting from a Levy–Lieb-type functional, ...
  • Kvaal, Simen; Laestadius, Andre; Bodenstein, Tilmann (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2020)
    A wide class of coupled-cluster methods is introduced, based on Arponen's extended coupled-cluster theory. This class of methods is formulated in terms of a coordinate transformation of the cluster operators. The mathematical ...
  • Pedersen, Thomas Bondo; Kristiansen, Håkon Emil; Bodenstein, Tilmann; Kvaal, Simen; Schøyen, Øyvind Sigmundson (Journal article / Tidsskriftartikkel / PublishedVersion; Peer reviewed, 2020)
    We demonstrate theoretically and numerically that laser-driven many-electron dynamics, as described by bivariational time-dependent coupled-cluster theory, may be analyzed in terms of stationary-state populations. Projectors ...
  • Kristiansen, Håkon Emil; Schøyen, Øyvind Sigmundson; Kvaal, Simen; Pedersen, Thomas Bondo (Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2020)
    We investigate the numerical stability of time-dependent coupled-cluster theory for many-electron dynamics in intense laser pulses, comparing two coupled-cluster formulations with full configuration interaction theory. Our ...
  • Pedersen, Thomas Bondo; Kvaal, Simen (Journal article / Tidsskriftartikkel / AcceptedVersion; Peer reviewed, 2019)
    The formulation of the time-dependent Schrödinger equation in terms of coupled-cluster theory is outlined, with emphasis on the bivariational framework and its classical Hamiltonian structure. An indefinite inner product ...