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The issue of orbital relaxation in computational core-hole spectroscopy, specifically x-ray absorption, has been a major problem for methods such as equation-of-motion coupled cluster with singles and doubles (EOM-CCSD). The…

Chemical Physics · Physics 2025-03-26 Megan Simons , Devin A. Matthews

A dynamical formulation of coupled cluster theory is derived using a variational principle. By allowing time-dependent single-particle functions, a high degree of adaptivity is introduced, allowing complex systems to be simulated with high…

Quantum Physics · Physics 2014-11-25 Simen Kvaal

While providing a highly accurate framework for simulating laser-induced many-electron dynamics in atom and molecules, including linear and nonlinear steady-state and transient absorption spectra, time-dependent coupled-cluster theory does…

The tailored coupled cluster (TCC) approach is a promising ansatz that preserves the simplicity of single-reference coupled cluster theory, while incorporating a multi-reference wave function through amplitudes obtained from a preceding…

Chemical Physics · Physics 2021-01-07 Maximilian Mörchen , Leon Freitag , Markus Reiher

The curse of dimensionality (COD) limits the current state-of-the-art {\it ab initio} propagation methods for non-relativistic quantum mechanics to relatively few particles. For stationary structure calculations, the coupled-cluster (CC)…

Quantum Physics · Physics 2015-06-03 Simen Kvaal

We derive equations of motion for bivariational wave functions with orthogonal adaptive basis sets and specialize the formalism to the coupled cluster ansatz. The equations are related to the biorthogonal case in a transparent way, and…

Chemical Physics · Physics 2023-11-06 Mads Greisen Højlund , Alberto Zoccante , Ove Christiansen

Wave functions based on electron-pair states provide inexpensive and reliable models to describe quantum many-body problems containing strongly-correlated electrons, given that broken-pair states have been appropriately accounted for by,…

Chemical Physics · Physics 2021-03-17 Artur Nowak , Ors Legeza , Katharina Boguslawski

In parallel with the evolution of femtosecond and attosecond laser as well as free-electron laser technology, a variety of theoretical methods have been developed to describe the behavior of atoms, molecules, clusters, and solids under the…

Atomic Physics · Physics 2015-11-12 Kenichi L. Ishikawa , Takeshi Sato

A time-dependent equation of motion coupled cluster singles and doubles (TD-EOM-CCSD) method is implemented, which uses a reduced basis calculated with the asymmetric band Lanczos algorithm. The approach is used to study weak-field…

An electrodynamical coupled cluster (CC) methodology starting from a covariant formalism and an equal time approximation, and finally based on the Dirac-Fock picture of the electron and positron fields and Coulomb gauge, is given here. The…

Atomic Physics · Physics 2019-04-30 Sambhu N. Datta

Quantum embedding methods have recently developed significantly to model large molecular structures. This work proposes a novel wave function theory in density functional theory (WTF-in-DFT) embedding scheme based on pair-coupled cluster…

Chemical Physics · Physics 2024-01-10 Rahul Chakraborty , Katharina Boguslawski , Paweł Tecmer

We present a wave-function based method to solve the time-dependent many-electron Schr\"odinger equation (TDSE) with special emphasis on strong-field ionization phenomena. The theory builds on the configuration-interaction (CI) approach…

Quantum Physics · Physics 2014-12-11 Sebastian Bauch , Lasse Kragh Sørensen , Lars Bojer Madsen

Time-dependent quantum chemical methods coupled to Gaussian basis sets are gaining popularity in modeling the electron dynamics of atoms and molecules interacting with intense laser fields. Two approaches most widely used for this purpose,…

Chemical Physics · Physics 2023-01-18 Aleksander P. Woźniak , Maciej Lewenstein , Robert Moszyński

In order to explore the effects of high levels of electron correlation on the real-time coupled cluster formalism and algorithmic behavior, we introduce a time-dependent implementation of the CC3 singles, doubles and approximate triples…

Chemical Physics · Physics 2025-01-23 Zhe Wang , Håkon Emil Kristiansen , Thomas Bondo Pedersen , T. Daniel Crawford

We present the quantum-selected configuration interaction-tailored coupled-cluster (QSCI-TCC) method, a hybrid quantum-classical scheme that tailors coupled-cluster (CC) theory with a quantum-selected configuration interaction (QSCI) wave…

Chemical Physics · Physics 2025-06-23 Luca Erhart , Yuichiro Yoshida , Wataru Mizukami

With growing demand for time-domain simulations of correlated many-body systems, the development of efficient and stable integration schemes for the time-dependent Schr\"odinger equation is of keen interest in modern electronic structure…

Chemical Physics · Physics 2023-08-22 David B. Williams-Young , Stephen Yuwono , A. Eugene DePrince , Chao Yang

We describe the time-dependent restricted-active-space self-consistent-field (TD-RASSCF) method for a system of interacting bosons. We provide the theory of the method and discuss its numerical implementation. The method provides a general…

Quantum Physics · Physics 2017-04-28 Camille Lévêque , Lars Bojer Madsen

We present a numerical implementation of the time-dependent surface flux (tSURFF) method [New J. Phys. 14, 013021 (2012)], an efficient computational scheme to extract photoelectron energy spectra, to the time-dependent multiconfiguration…

Atomic Physics · Physics 2019-08-07 Yuki Orimo , Takeshi Sato , Kenichi L. Ishikawa

Time-dependent equation-of-motion coupled cluster (TD-EOM-CC) is used to simulate impulsive stimulated x-ray Raman scattering (ISXRS) of ultrashort laser pulses by neon, carbon monoxide, pyrrole, and p-aminophenol. The TD-EOM-CC equations…

Chemical Physics · Physics 2023-10-10 Alice Balbi , Andreas S. Skeidsvoll , Henrik Koch

The problem of orbital relaxation in computational core-hole spectroscopies, including x-ray absorption and x-ray photoionization, has long plagued linear response approaches, including equation-of-motion coupled cluster with singles and…

Chemical Physics · Physics 2025-03-26 Megan E. Simons , Devin A. Matthews