• An efficient algorithm for Cholesky decomposition of electron repulsion integrals 

      Folkestad, Sarai Dery; Kjønstad, Eirik Fadum; Koch, Henrik (Journal article; Peer reviewed, 2019)
      Approximating the electron repulsion integrals using inner projections is a well-established approach to reduce the computational demands of electronic structure calculations. Here, we present a two-step Cholesky decomposition ...
    • An Orbital Invariant Similarity Constrained Coupled Cluster Model 

      Kjønstad, Eirik Fadum; Koch, Henrik (Journal article; Peer reviewed, 2019)
      We present a similarity constrained coupled cluster method able to describe conical intersections between two excited electronic states of the same symmetry. For a given pair of states, this singles and doubles method ...
    • Crossing conditions in coupled cluster theory 

      Kjønstad, Eirik Fadum; Heilemann Myhre, Rolf; Martinez, Todd J.; Koch, Henrik (Journal article; Peer reviewed, 2017)
      We derive the crossing conditions at conical intersections between electronic states in coupled cluster theory and show that if the coupled cluster Jacobian matrix is nondefective, two (three) independent conditions are ...
    • Modeling Chemistry in QED Cavities using Coupled Cluster 

      Haugland, Tor Strømsem (Master thesis, 2019)
      I denne avhandlingen introduseres kvanteelektrodynamisk ''coupled cluster'' teori (QED-CC) som en ny og nøyaktig ab initio teori for å undersøke sterk kobling mellom lys og materie i optiske kaviteter. Ligningene for ...
    • Resolving the Notorious Case of Conical Intersections for Coupled Cluster Dynamics 

      Kjønstad, Eirik Fadum; Koch, Henrik (Journal article; Peer reviewed, 2017)
      The motion of electrons and nuclei in photochemical events often involves conical intersections, or degeneracies between electronic states. They serve as funnels in nuclear relaxation processes where the electrons and ...
    • Spin adapted implementation of EOM-CCSD for triplet excited states: Probing intersystem crossings of acetylacetone at the carbon and oxygen K-edges 

      Faber, Rasmus; Kjønstad, Eirik Fadum; Koch, Henrik; Coriani, Sonia (Journal article; Peer reviewed, 2019)
      We present an equation of motion coupled cluster singles and doubles approach for computing transient absorption spectra from a triplet excited state. The implementation determines the left and right excitation vectors by ...
    • Symmetric Coupled Cluster Theory 

      Kjønstad, Eirik Fadum (Master thesis, 2016)
      We introduce a novel coupled cluster formulation for the ground state, symmetric coupled cluster (SCC) theory, and an extension to excited states, molecular properties, and transition elements called symmetric equation of ...