145 citations · 275 across the 16 of their papers we have counts for
18 papers
The RAS-CCSD model, with applications for open-shell molecules
Sarai Dery Folkestad
The restricted active space coupled cluster singles and doubles (RAS-CCSD) model, and its pilot implementation is detailed. The approach offers a simple, pragmatic way to formulate…
Coupled cluster theory for multireference and open-shell molecules
Sarai Dery Folkestad, Henrik Koch
We introduce a simple coupled cluster approach for multireference and open-shell systems. In the restricted active space coupled cluster framework, the cluster operator only includ…
The role of charge resonances in the benzene dimer
Alice Balbi, Andrea Rygg Aagaard, Sarai Dery Folkestad +1
Modern electronic-structure theory defines dispersion interactions as connected intramonomer excitations. Using this definition, dispersion contributions have been shown in literat…
eT 2.0: An efficient open-source molecular electronic structure program
Sarai Dery Folkestad, Eirik F. Kjønstad, Alexander C. Paul +34
The eT program is an open-source electronic structure program with emphasis on performance and modularity. As its name suggests, the program features extensive coupled cluster capa…
An orthogonal electronic state view on charge delocalization and transfer
Sarai Dery Folkestad, Ida-Marie Høyvik
We present a configuration interaction (CI) framework which serves quantitative and conceptual purposes for charge delocalization and electron transfer processes in molecular syste…
Excitation Energies from the Entanglement Coupled Cluster Model for Doublets
Sarai Dery Folkestad, Kristine Lauvstad Kruken, Henrik Koch
We present excitation energies for molecular doublets from a spin-adapted formulation of coupled cluster singles and doubles theory. The entanglement coupled cluster approach repre…
X-ray Absorption Spectra for Aqueous Ammonia and Ammonium: Quantum Mechanical versus Molecular Mechanical Embedding Schemes
Sarai Dery Folkestad, Alexander C. Paul, Regina Paul +4
The X-ray absorption (XA) spectra of aqueous ammonia and ammonium are computed using a combination of coupled cluster singles and doubles (CCSD) with different quantum mechanical a…
Understanding X-ray absorption in liquid water: triple excitations in multilevel coupled cluster theory
Sarai Dery Folkestad, Alexander C. Paul, Regina Paul +4
We present the first successful application of the coupled cluster approach to simulate the X-ray absorption (XA) spectrum of liquid water. The system size limitations of standard…
Entanglement Coupled Cluster Theory: Exact Spin-Adaptation
Sarai Dery Folkestad, Bendik Støa Sannes, Henrik Koch
We present a novel approach to spin-adapted coupled cluster theory. This approach is based on the entanglement of an open-shell molecule with electrons in a non-interacting bath; t…
New Implementation of an Equation-of-Motion Coupled-Cluster Damped-Response Framework with Illustrative Applications to Resonant Inelastic X-ray Scattering
Anna Kristina Schnack-Petersen, Torsha Moitra, Sarai Dery Folkestad +1
We present an implementation of a damped response framework for calculating resonant inelastic X-ray scattering (RIXS) at the equation-of-motion coupled cluster singles and doubles…
Oscillator strengths in the framework of equation of motion multilevel CC3
Alexander C. Paul, Sarai D. Folkestad, Rolf H. Myhre +1
We present an efficient implementation of the equation of motion oscillator strengths for the closed-shell multilevel coupled cluster singles and doubles with perturbative triples…
Combining Multilevel Hartree Fock and Multilevel Coupled Cluster with Molecular Mechanics: a Study of Electronic Excitations in Solutions
Linda Goletto, Tommaso Giovannini, Sarai D. Folkestad +1
We investigate the coupling of different quantum-embedding approaches with a third molecular-mechanics layer, which can be either polarizable or non-polarizable. In particular, suc…
Transient Resonant Auger-Meitner Spectra of Photoexcited Thymine
Thomas J. A. Wolf, Alexander C. Paul, Sarai D. Folkestad +15
We present the first investigation of excited state dynamics by resonant Auger-Meitner spectroscopy (also known as resonant Auger spectroscopy) using the nucleobase thymine as an e…
Equation-of-motion MLCCSD and CCSD-in-HF oscillator strengths and their application to core excitations
Sarai D. Folkestad, Henrik Koch
We present an implementation of equation-of-motion oscillator strengths for the multilevel CCSD (MLCCSD) model where CCS is used as the lower level method (CCS/CCSD). In this model…
Multilevel CC2 and CCSD in reduced orbital spaces: electronic excitations in large molecular systems
Sarai D. Folkestad, Eirik F. Kjønstad, Linda Goletto +1
We present efficient implementations of the multilevel CC2 (MLCC2) and multilevel CCSD (MLCCSD) models. As the system size increases, MLCC2 and MLCCSD exhibit the scaling of the lo…
Accelerated multimodel Newton-type algorithms for faster convergence of ground and excited state coupled cluster equations
Eirik F. Kjønstad, Sarai D. Folkestad, Henrik Koch
We introduce a multimodel approach to solve coupled cluster equations, employing a quasi Newton algorithm for the ground state and an Olsen algorithm for the excited states. In the…
eT 1.0: an open source electronic structure program with emphasis on coupled cluster and multilevel methods
Sarai D. Folkestad, Eirik F. Kjønstad, Rolf H. Myhre +14
The eT program is an open source electronic structure package with emphasis on coupled cluster and multilevel methods. It includes efficient spin adapted implementations of ground…
An efficient algorithm for Cholesky decomposition of electron repulsion integrals
Sarai D. Folkestad, Eirik F. Kjønstad, Henrik Koch
We present an algorithm where only the Cholesky basis is determined in the decomposition procedure. This allows for improved screening and a partitioned matrix decomposition scheme…