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We present the implementation of quadratic response theory based upon the relativistic equation-of-motion coupled cluster method. We showcase our implementation, whose generality allows us to consider both time-dependent and…

Chemical Physics · Physics 2024-01-29 Xiang Yuan , Loic Halbert , Lucas Visscher , Andre Severo Pereira Gomes

We report the implementation of equation-of-motion coupled-cluster (EOMCC) method in the four-component relativistic framework with the spherical atomic potential to generate the excited states from a closed-shell atomic configuration. This…

Atomic Physics · Physics 2015-06-19 D. K. Nandy , Yashpal Singh , B. K. Sahoo

A relativistic version of the effective charge model for computation of observable characteristics of multi-electron atoms and ions is developed. A complete and orthogonal Dirac hydrogen basis set, depending on one parameter -- effective…

Atomic Physics · Physics 2020-07-10 K. Dzikowski , O. D. Skoromnik , I. D. Feranchuk , N. S. Oreshkina , C. H. Keitel

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 (CCSD) and second-order approximate coupled cluster singles…

We show that numerical linked cluster expansions (NLCEs) based on sufficiently large building blocks allow one to obtain accurate low-temperature results for the thermodynamic properties of spin lattice models with continuous disorder…

Statistical Mechanics · Physics 2024-06-04 Mahmoud Abdelshafy , Marcos Rigol

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

An accurate analytical parametrization for the exchange-correlation free energy of the homogeneous electron gas, including interpolation for partial spin-polarization, is derived via thermodynamic analysis of recent restricted path integral…

Chemical Physics · Physics 2015-06-17 Valentin V. Karasiev , Travis Sjostrom , James Dufty , S. B. Trickey

In this paper, we have developed a unitary variant of a double exponential coupled cluster theory, which is capable of mimicking the effects of connected excitations of arbitrarily high rank, using only rank-one and rank-two parametrization…

Chemical Physics · Physics 2022-11-23 Dipanjali Halder , V. S. Prasannaa , Rahul Maitra

We present an efficient implementation of a one-step relativistic second-order multireference perturbation theory based on the multireference driven similarity renormalization group (MR-DSRG) using the exact two-component (X2C) Hamiltonian,…

Chemical Physics · Physics 2026-05-13 Zijun Zhao , Francesco A. Evangelista

An investigation of the validity of the semiclassical approximation to quantum electrodynamics in 1+1 dimensions is given. The criterion for validity used here involves the impact of quantum fluctuations introduced through a two-point…

General Relativity and Quantum Cosmology · Physics 2025-05-02 Ian M. Newsome , Paul R. Anderson , Eric M. Grotzke

We present the theory and the implementation of a low-cost four-component relativistic equation of motion coupled cluster method for ionized states based on frozen natural spinors. A single threshold (natural spinor occupancy) can control…

Chemical Physics · Physics 2024-06-19 Kshitijkumar Surjuse , Somesh Chamoli , Malaya K. Nayak , Achintya Kumar Dutta

In this paper, an efficient implementation of the renormalized internally-contracted multreference coupled cluster with singles and doubles (RIC-MRCCSD) into the ORCA quantum chemistry program suite is reported. To this end, Evangelista's…

Chemical Physics · Physics 2026-04-24 Kalman Szenes , Riya Kayal , Kantharuban Sivalingam , Robin Feldmann , Frank Neese , Markus Reiher

We have implemented relativistic formulations of DIP-EOMCCSD and DIP-EOMCCSDT within the 1eX2C and DC-, DCG-, and DCB-X2C frameworks. Direct comparisons against full 4c-DIP-EOMCCSD calculations show excellent agreement with…

We investigate the charge- and spin dynamical structure factors for the 2D one-band Hubbard model in the strong coupling regime within an extension of the Dynamical Cluster Approximation (DCA) to two-particle response functions. The full…

Strongly Correlated Electrons · Physics 2009-11-13 S. Hochkeppel , F. F. Assaad , W. Hanke

We have developed a relativistic coupled-cluster theory to incorporate nuclear spin-dependent interaction Hamiltonians perturbatively. This theory is ideal to calculate parity violating nuclear spin-dependent electric dipole transition…

Atomic Physics · Physics 2011-06-09 B. K. Mani , D. Angom

The dielectric behavior of a linear cluster of two or more living cells connected by tight junctions is analyzed using a spectral method. The polarizability of this system is obtained as an expansion over the eigenmodes of the linear…

Biological Physics · Physics 2010-02-12 Titus Sandu , Daniel Vrinceanu , Eugen Gheorghiu

In spin-adapted open-shell coupled cluster (CC) theory, the choice of spin-free spatial substitution operators is generally not unique. Due to an increasing linear dependence of the cluster operator (with increasing substitution level), the…

Chemical Physics · Physics 2022-04-27 Nils Herrmann , Michael Hanrath

We report an efficient implementation of the ionization potential (IP) variant of the equation-of-motion coupled cluster (IP-EOM-CC) method based on the exact two-component atomic mean field (X2CAMF) framework, utilizing Cholesky…

Chemical Physics · Physics 2025-06-10 Somesh Chamoli , Malaya K. Nayak , Achintya Kumar Dutta

We present an efficient implementation of the second-order two-component relativistic core-valence-separated algebraic diagrammatic construction method (CVS-ADC(2)) for core-excitation calculations. The approach employs state-averaged…

Chemical Physics · Physics 2026-05-01 Somesh Chamoli , Sudipta Chakraborty , Xubo Wang , Achintya Kumar Dutta

The focus of this work is OS-CCSD-SPT(2), which is a second-order similarity transformed perturbation theory correction to opposite spin coupled cluster singles doubles, where in the latter the same-spin amplitudes are removed and the…

Chemical Physics · Physics 2020-03-16 David W. Small