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Based on self-consistent field (SCF) atomic mean-field (amf) quantities, we present two simple, yet computationally efficient and numerically accurate matrix-algebraic approaches to correct both scalar-relativistic \textit{and} spin-orbit…

Chemical Physics · Physics 2023-02-03 Stefan Knecht , Michal Repisky , Hans Jørgen Aagaard Jensen , Trond Saue

We report an efficient algorithm using density fitting for the relativistic complete active space self-consistent field (CASSCF) method, which is significantly more stable than the algorithm previously reported by one of the authors [J. E.…

Chemical Physics · Physics 2018-08-01 Ryan D. Reynolds , Takeshi Yanai , Toru Shiozaki

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

Since its inception, the ReSpect program has been evolving to provide powerful tools for simulating spectroscopic processes and exploring emerging research areas, all while incorporating relativistic effects, particularly spin-orbit…

We present a simple relativistic exact 2-component (X2C) Hamiltonian that models two-electron picture-change effects using Lehtola's superposition of atomic potentials (SAP) [S. Lehtola, J. Chem. Theory Comput. 15, 1593-1604 (2019)]. The…

Chemical Physics · Physics 2026-03-10 Kshitijkumar A. Surjuse , Edward F. Valeev

A new computational framework for spinor-based relativistic exact two-component (X2C) calculations is developed using contracted basis sets with a spin-orbit contraction scheme. Generally contracted j-adapted basis sets using primitive…

Chemical Physics · Physics 2024-05-08 Chaoqun Zhang , Kirk A. Peterson , Kenneth G. Dyall , Lan Cheng

We report an approach for determination of zero-field splitting parameters from four-component relativistic calculations. Our approach involves neither perturbative treatment of spin-orbit interaction nor truncation of the spin-orbit…

Chemical Physics · Physics 2019-03-26 Ryan D. Reynolds , Toru Shiozaki

In this work, we develop a new orbital optimization approach, perturbative Super-CI (Super-CIPT), for the two-component complete active space self-consistent field (2C-CASSCF) method. By variationally optimizing spinor orbitals and…

Chemical Physics · Physics 2026-03-04 Yang Guo , Achintya Kumar Dutta

Materials utilized by novel energy systems are often studied using weakly correlated mean-field theories. However, if these systems incorporate heavy elements, relativistic effects must be included. Therefore a Kramers unrestricted Coupled…

Materials Science · Physics 2026-05-21 Luca Murg , Christopher Lane , Roxanne M. Tutchton

The development of relativistic exact two-component (X2C) theory is briefly reviewed, with an emphasis on cost-effective treatments of relativistic two-electron contributions by means of model potential (MP) techniques and closely related…

Chemical Physics · Physics 2025-04-29 Xubo Wang , Chaoqun Zhang , Junzi Liu , Lan Cheng

We present the formulation and implementation of triples correction scheme to the relativistic equation-of-motion coupled-cluster method for ionization potential. Both full and partial triples correction schemes are implemented using the…

Chemical Physics · Physics 2026-03-31 Mrinal Thapa , Achinyta Kumar Dutta

We present an efficient implementation of the low-cost linear-response coupled-cluster singles and doubles (LR-CCSD) method for computing static and frequency-dependent polarizabilities in systems with significant relativistic and…

Chemical Physics · Physics 2026-04-15 Sudipta Chakraborty , Muskan Begom , Xubo Wang , Achintya Kumar Dutta

It is shown that four-component (4C), quasi-four-component (Q4C), and exact two-component (X2C) relativistic Hartree-Fock (HF) equations can be implemented in an unified manner, by making use of the atomic nature of the small components of…

Chemical Physics · Physics 2023-11-28 Wenjian Liu

X-ray absorption spectroscopy (XAS) has gained popularity in recent years as it probes matter with high spatial and elemental sensitivity. However, the theoretical modelling of XAS is a challenging task since XAS spectra feature a fine…

Chemical Physics · Physics 2023-02-03 Lukas Konecny , Stanislav Komorovsky , Jan Vicha , Kenneth Ruud , Michal Repisky

The complete active space self-consistent field (CASSCF) method is the principal approach employed for studying strongly correlated systems. However, exact CASSCF can only be performed on small active spaces of ~20 electrons in ~20 orbitals…

Computational Physics · Physics 2021-12-22 Daniel S. Levine , Diptarka Hait , Norm M. Tubman , Susi Lehtola , K. Birgitta Whaley , Martin Head-Gordon

We present an efficient algorithm for one- and two-component relativistic exact-decoupling calculations. Spin-orbit coupling is thus taken into account for the evaluation of relativistically transformed (one-electron) Hamiltonian. As the…

Chemical Physics · Physics 2013-05-10 Daoling Peng , Nils Middendorf , Florian Weigend , Markus Reiher

We present a formulation of relativistic self-consistent $GW$ for solids based on the exact two-component formalism with one-electron approximation (X2C1e) and non-relativistic Coulomb interactions. Our theory allows us to study scalar…

Strongly Correlated Electrons · Physics 2022-08-31 Chia-Nan Yeh , Avijit Shee , Qiming Sun , Emanuel Gull , Dominika Zgid

A Cholesky decomposition (CD)-based implementation of relativistic two-component coupled-cluster (CC) and equation-of-motion CC (EOM-CC) methods using an exact two-component Hamiltonian augmented with atomic-mean-field spin-orbit integrals…

Chemical Physics · Physics 2023-09-19 Chaoqun Zhang , Filippo Lipparini , Stella Stopkowicz , Jürgen Gauss , Lan Cheng

We present a novel implementation of the complete active space self-consistent field (CASSCF) method that makes use of the many-body expanded full configuration interaction (MBE-FCI) method to incrementally approximate electronic structures…

We have presented the theory, implementation, and benchmark results for the one-electronic variant of spin-free exact two-component (SFX2C1e) linear response coupled cluster (LRCCSD) theory for static and dynamic polarizabilities of atoms…

Chemical Physics · Physics 2024-05-31 Sudipta Chakraborty , Tamoghna Mukhopadhyay , Achintya Kumar Dutta
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