Post-CCSD(T) Thermochemistry of Chlorine Fluorides as a Challenging Test Case for Evaluating Density Functional Theory and Composite Ab Initio Methods

Author(s)
Karton, Amir
Haasler, Matthias
Kaupp, Martin
Publication Date
2025-02-01
Abstract
<p>Quantum chemistry plays a key role in exploring the chemical properties of highly reactive chlorine polyfluoride compounds (ClF<i><sub>n</sub></i>). Here, we investigate the thermochemical properties of ClF<i><sub>n</sub></i> species (<i>n</i>=2–6) by means of high-level thermochemical procedures approximating the CCSDT(Q) and CCSDTQ5 energies at the complete basis set limit. We consider total atomization energies (TAEs), Cl F bond dissociation energies (BDEs), F<sub>2</sub> elimination energies (F<sub>2</sub> elim.), ionization potentials (IPs), and electron affinities (EAs). The TAEs have significant contributions from post-CCSD(T) correlation effects. The higher-order triple excitations, CCSDT CCSD(T), are negative and amount to 0.338 (ClF<sub>2</sub>), 0.727 (ClF<sub>3</sub>), 0.903 (ClF<sub>4</sub>), 1.335 (ClF<sub>5</sub>), and 1.946 (ClF<sub>6</sub>) kcal/mol. However, the contributions from quadruple (and, where available, also quintuple) excitations are much larger and positive and amount to +1.335 (ClF<sub>2</sub>), +1.387 (ClF<sub>3</sub>), +2.367 (ClF<sub>4</sub>), +2.399 (ClF<sub>5</sub>), and +3.432 (ClF<sub>6</sub>) kcal/mol. Thus, the contributions from post-CCSD(T) excitations exceed the threshold of chemical accuracy in nearly all cases. Due to their increasing hyper-valency and multireference character, the ClF<i><sub>n</sub></i> series provides an interesting and challenging test case for both density functional theory and low-level composite ab initio procedures. Here, we highlight the limitations in achieving overall chemical accuracy across all DFT and most composite ab initio procedures.</p>
Citation
ChemPhysChem, 26(3), p. 1-11
ISSN
1439-7641
1439-4235
Link
Publisher
Wiley-VCH Verlag GmbH & Co KGaA
Title
Post-CCSD(T) Thermochemistry of Chlorine Fluorides as a Challenging Test Case for Evaluating Density Functional Theory and Composite Ab Initio Methods
Type of document
Journal Article
Entity Type
Publication

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