Two-Component Relativistic Equation-of-Motion Coupled-Cluster Methods for Excitation Energies and Ionization Potentials of Atoms and Molecules

Akinaga, Yoshinobu; Nakajima, Takahito

doi:10.1021/acs.jpca.6b10921

Cited by 28 publications

(29 citation statements)

References 89 publications

(142 reference statements)

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“…The appealing features of EOM-CC have made it an extremely popular method for light element systems, and its popularity is growing for heavier species as attested by the number of recent reports in the literature of EOM-CC implementations that take into account relativistic effects. Though some of the latter are based on solving the four-component (4C) Dirac equation for atomic and molecular systems [69][70][71][72][73] and therefore account rigorously for scalar relativistic (SR) effects and spin-orbit coupling (SOC), for reasons of computational efficiency most of them [74][75][76][77][78][79][80][81][82] have been devised in a more approximate framework where SOC is treated to within different degrees of approximation e.g. starting from the spin-free exact two-component (sfX2C) Hamiltonian and including SOC via atomic mean-field (AMF) integrals 83 or perturbatively.…”

Section: Introductionmentioning

confidence: 99%

Equation-of-motion coupled-cluster theory based on the 4-component Dirac–Coulomb(–Gaunt) Hamiltonian. Energies for single electron detachment, attachment, and electronically excited states

Shee

Saue

Visscher

et al. 2018

The Journal of Chemical Physics

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We report in this paper an implementation of 4-component relativistic Hamiltonian based Equation-of-Motion Coupled-Cluster with singles and doubles (EOM-CCSD) theory for the calculation of ionization potential (IP), electron affinity (EA) and excitation energy (EE). In this work we utilize previously developed double group symmetry-based generalized tensor contraction scheme, and also extend it in order to carry out tensor contractions involving non-totally symmetric and odd-ranked tensors. Several approximated spin-free and two-component Hamiltonians can also be accessed in this implementation. We have applied this method to the halogen monoxide (XO, X= Cl, Br, I, At, Ts) species, in order to assess the quality of a few other recent EOM-CCSD implementations, where spin-orbit coupling contribution has been approximated in different degree. Besides, we also have studied various excited states of CH 2 IBr, CH 2 I 2 and I − 3 (as well as single electron attachment and detachment electronic states of the same species) where comparison has been made with a closely related multi-reference coupled-cluster method, namely Intermediate Hamiltonian Fock Space Coupled-Cluster singles and doubles (IHFS-CCSD) theory.

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Section: Introductionmentioning

confidence: 99%

Equation-of-motion coupled-cluster theory based on the 4-component Dirac–Coulomb(–Gaunt) Hamiltonian. Energies for single electron detachment, attachment, and electronically excited states

Shee

Saue

Visscher

et al. 2018

The Journal of Chemical Physics

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“…A notable feature of the ground‐ and excited‐state implementations discussed here is that they rely on the same template metaprogramming techniques employed throughout the rest of ChronusQ (see Appendix) and thus are compatible with both real and complex RHF, UHF, and GHF (including X2C‐HF) reference wave functions. Hence, like many other reported implementations of time‐independent relativistic EOM‐CC theory, the X2C‐based TD‐EOM‐CC2 and TD‐EOM‐CCSD algorithms in ChronusQ incorporate spin‐orbit and scalar relativistic effects from first principles. To the best of the authors' knowledge, this implementation is the only one that incorporates spin‐orbit coupling within a TD EOM‐CC formalism at this time.…”

Section: Current Developmentsmentioning

confidence: 94%

The Chronus Quantum software package

Williams‐Young

Petrone

Sun

et al. 2019

WIREs Comput Mol Sci

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The Chronus Quantum (ChronusQ) software package is an open source (under the GNU General Public License v2) software infrastructure which targets the solution of challenging problems that arise in ab initio electronic structure theory. Special emphasis is placed on the consistent treatment of time dependence and spin in the electronic wave function, as well as the inclusion of relativistic effects in said treatments. In addition, ChronusQ provides support for the inclusion of uniform finite magnetic fields as external perturbations through the use of gauge‐including atomic orbitals. ChronusQ is a parallel electronic structure code written in modern C++ which utilizes both message passing implementation and shared memory (OpenMP) parallelism. In addition to the examination of the current state of code base itself, a discussion regarding ongoing developments and developer contributions will also be provided. This article is categorized under: Software > Quantum Chemistry Electronic Structure Theory > Ab Initio Electronic Structure Methods Electronic Structure Theory > Density Functional Theory

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“…It is just that the breaking of spin symmetry and the concurrent appearance of complex algebra in the presence of spin-orbit coupling (SOC) render not only the implementation difficult but also the computation expensive. Nevertheless, many sophisticated relativistic correlated wave function methods have been made available for use, including four-(4C) or two-component (2C) many-body perturbation theory [22,23], coupled-cluster [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43], configuration interaction (CI) [44][45][46][47][48][49][50][51], multiconfiguration self-consistent field [52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67]…”

Section: Introductionmentioning

confidence: 99%

SOiCI and iCISO: Combining iterative configuration interaction with spin-orbit coupling in two ways

Zhang,

Xiao,

Liu

2022

Preprint

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The near-exact iCIPT2 approach for strongly correlated systems of electrons, which stems from the combination of iterative configuration interaction (iCI, an exact solver of full CI) with configuration selection for static correlation and second-order perturbation theory (PT2) for dynamic correlation, is extended to the relativistic domain. In the spirit of spin separation, relativistic effects are treated in two steps: scalar relativity is treated by the infinite-order, spin-free part of the exact two-component (X2C) relativistic Hamiltonian, whereas spin-orbit coupling (SOC) is treated by the first-order, Douglas-Kroll-Hess-like SOC operator derived from the same X2C Hamiltonian. Two possible combinations of iCIPT2 with SOC are considered, i.e., SOiCI and iCISO. The former treats SOC and electron correlation on an equal footing, whereas the latter treats SOC in the spirit of state interaction, by constructing and diagonalizing an effective spin-orbit Hamiltonian matrix in a small number of correlated scalar states. Both double group and time reversal symmetries are incorporated to simplify the computation. Pilot applications reveal that SOiCI is very accurate for the spin-orbit splitting (SOS) of heavy atoms, whereas the computationally very cheap iCISO can safely be applied to the SOS of light atoms and even of systems containing heavy atoms when SOC is largely quenched by ligand fields.

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Two-Component Relativistic Equation-of-Motion Coupled-Cluster Methods for Excitation Energies and Ionization Potentials of Atoms and Molecules

Cited by 28 publications

References 89 publications

Equation-of-motion coupled-cluster theory based on the 4-component Dirac–Coulomb(–Gaunt) Hamiltonian. Energies for single electron detachment, attachment, and electronically excited states

Equation-of-motion coupled-cluster theory based on the 4-component Dirac–Coulomb(–Gaunt) Hamiltonian. Energies for single electron detachment, attachment, and electronically excited states

The Chronus Quantum software package

SOiCI and iCISO: Combining iterative configuration interaction with spin-orbit coupling in two ways

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