A Comparison of the Interacting Quantum Atoms (IQA) Analysis of the Two‐Particle Density‐Matrices of MP4SDQ and CCSD

Vincent, Mark A.; Silva, Arnaldo F.; Popelier, Paul L. A.

doi:10.1002/zaac.202000169

Cited by 8 publications

(8 citation statements)

References 27 publications

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“…Popelier et al analysed the effects of electron correlation within atoms and between atoms, bonded or not, under the MP2 approximation [ 70 ] and later on examined how higher orders of perturbation theory affect electronic correlation [ 71 ]. More recently, the same authors compared intra- and interatomic electron correlation energies resulting from of MP4SDQ and CCSD calculations finding that the later produces correlation energies that are much larger in magnitude [ 72 ]. Casals-Sainz used IQA in combination with CCSD(T) coupled cluster densities to investigate the spatial distribution of electronic correlation.…”

Section: Selected Applications Of the Iqa Methodologymentioning

confidence: 99%

Interacting Quantum Atoms—A Review

et al. 2020

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The aim of this review is threefold. On the one hand, we intend it to serve as a gentle introduction to the Interacting Quantum Atoms (IQA) methodology for those unfamiliar with it. Second, we expect it to act as an up-to-date reference of recent developments related to IQA. Finally, we want it to highlight a non-exhaustive, yet representative set of showcase examples about how to use IQA to shed light in different chemical problems. To accomplish this, we start by providing a brief context to justify the development of IQA as a real space alternative to other existent energy partition schemes of the non-relativistic energy of molecules. We then introduce a self-contained algebraic derivation of the methodological IQA ecosystem as well as an overview of how these formulations vary with the level of theory employed to obtain the molecular wavefunction upon which the IQA procedure relies. Finally, we review the several applications of IQA as examined by different research groups worldwide to investigate a wide variety of chemical problems.

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Section: Selected Applications Of the Iqa Methodologymentioning

confidence: 99%

Interacting Quantum Atoms—A Review

et al. 2020

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“…However, for CCSD, an electron density is employed that now includes correlation. We have observed in ref [162] that CCSD picks up more subtle effects than MP4SDQ. In summary, CCSD is the way forward but I wish that MPn would numerically be closer to it.…”

Section: Replymentioning

confidence: 98%

“…However, this shortcoming does not harm the development of FFLUX, which only uses V AA � c anyway. In 2015, IQA became linked [161] with coupled cluster theory, and in 2020 our own CCSD-IQA version [162] made it possible to compare its V AB c values with MP2-based ones. We noticed a rule when studying [163] water clusters (up to pentamer) with IQA at MP2/6-31G** level.…”

Section: Electron Correlation Energymentioning

confidence: 99%

Non-covalent interactions from a Quantum Chemical Topology perspective

Popelier

2022

J Mol Model

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About half a century after its little-known beginnings, the quantum topological approach called QTAIM has grown into a widespread, but still not mainstream, methodology of interpretational quantum chemistry. Although often confused in textbooks with yet another population analysis, be it perhaps an elegant but somewhat esoteric one, QTAIM has been enriched with about a dozen other research areas sharing its main mathematical language, such as Interacting Quantum Atoms (IQA) or Electron Localisation Function (ELF), to form an overarching approach called Quantum Chemical Topology (QCT). Instead of reviewing the latter’s role in understanding non-covalent interactions, we propose a number of ideas emerging from the full consequences of the space-filling nature of topological atoms, and discuss how they (will) impact on interatomic interactions, including non-covalent ones. The architecture of a force field called FFLUX, which is based on these ideas, is outlined. A new method called Relative Energy Gradient (REG) is put forward, which is able, by computation, to detect which fragments of a given molecular assembly govern the energetic behaviour of this whole assembly. This method can offer insight into the typical balance of competing atomic energies both in covalent and non-covalent case studies. A brief discussion on so-called bond critical points is given, highlighting concerns about their meaning, mainly in the arena of non-covalent interactions.

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“…A few results on perturbation approaches are given also. , Additionally, MP4SDQ and CCSD levels were presented in the most recent report . However, the proposed formalism takes into account the correlation contribution for the electron interaction term only, thus ignoring the correlation impact on other energy components.…”

Section: Introductionmentioning

confidence: 99%

“…15,16 Additionally, MP4SDQ and CCSD levels were presented in the most recent report. 17 However, the proposed formalism takes into account the correlation contribution for the electron interaction term only, thus ignoring the correlation impact on other energy components. As it was recently discussed in ref 13 and will be shown in the present work, a large part of dynamic correlation is contained in kinetic T and electron−nuclei interaction U en energies.…”

Section: ■ Introductionmentioning

confidence: 99%

TWOE Code: An Efficient Tool for Explicit Partition of Coupled Cluster and Configuration Interaction Energies into Atomic and Diatomic Contributions

Polestshuk¹

2021

J. Phys. Chem. A

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The efficient implementation of the TWOE program for evaluating the atomic and interatomic energy components at post-HF level was developed. The systematic convergence of these terms up to a near full-CI limit was performed for the first time for a series of coupled cluster methods: CCSD → CCSDT → CCSDTQ → CCSDTQP. A comparison with corresponding CI approaches (up to fifth excitation level) is additionally discussed. For a set of diatomic systems, it was demonstrated that, along with a full molecular energy convergence, all its components are also converged but with different patterns. It was found that not all components are decreased in their values at increasing computational rank. For instance, atomic energy parts are decreased while interatomic (interaction) energies are increased as the limiting level is approached. Two schemes were employed for atomic partition of molecules: the Baders approach and planes dissection. Influence of dynamical correlation effects on atomic energy components was analyzed in detail. Current TWOE implementation allows one, in principle, to work with any ab initio method providing the two-particle density matrix. It is believed that the developed program will be a useful tool for a real space energy decomposition that helps to reveal the most peculiar points in the structure of the total and correlation energies of a molecule.

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A Comparison of the Interacting Quantum Atoms (IQA) Analysis of the Two‐Particle Density‐Matrices of MP4SDQ and CCSD

Cited by 8 publications

References 27 publications

Interacting Quantum Atoms—A Review

Interacting Quantum Atoms—A Review

Non-covalent interactions from a Quantum Chemical Topology perspective

TWOE Code: An Efficient Tool for Explicit Partition of Coupled Cluster and Configuration Interaction Energies into Atomic and Diatomic Contributions

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