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The acetylperoxy + HO 2 reaction has multiple impacts on the troposphere, with a triplet pathway leading to peracetic acid + O 2 (reaction (1a)) competing with singlet pathways leading to acetic acid + O 3 (reaction (1b)) and acetoxy + OH + O 2 (reaction (1c)). A recent experimental study has reported branching fractions for these three pathways ( α 1a , α 1b , and α 1c ) from 229 K to 294 K. We constructed a theoretical model for predicting α 1a , α 1b , and α 1c using quantum chemical and Rice–Ramsperger–Kassel–Marcus/master equation (RRKM/ME) simulations. Our main quantum chemical method was Weizmann-1 Brueckner Doubles (W1BD) theory; we combined W1BD and equation-of-motion spin-flip coupled cluster (SF) theory to treat open-shell singlet structures. Using RRKM/ME simulations that included all conformers of acetylperoxy–HO 2 pre-reactive complexes led to a 298 K triplet rate constant, k 1a = 5.11 × 10 −12 cm 3 per molecule per s, and values of α 1a in excellent agreement with experiment. Increasing the energies of all singlet structures by 0.9 kcal mol −1 led to a combined singlet rate constant, k 1b+1c = 1.20 × 10 −11 cm 3 per molecule per s, in good agreement with experiment. However, our predicted variations in α 1b and α 1c with temperature are not nearly as large as those measured, perhaps due to the inadequacy of SF theory in treating the transition structures controlling acetic acid + O 3 formation vs. acetoxy + OH + O 2 formation.
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Electron-phonon coupling and spin fluctuations in the Ising superconductor NbSe2
Abstract Ising superconductivity, observed in NbSe 2 and similar materials, has generated tremendous interest. Recently, attention was called to the possible role that spin fluctuations (SF) play in this phenomenon, in addition to the dominant electron–phonon coupling (EPC); the possibility of a predominantly triplet state was discussed and led to a conjecture of viable singlet–triplet Leggett oscillations. However, these hypotheses have not been put to a quantitative test. In this paper, we report first principle calculations of the EPC and also estimate coupling with SF, including full momentum dependence. We find that: (1) EPC is strongly anisotropic, largely coming from the $$K-{K}^{{\prime} }$$ K − K ′ scattering, and therefore excludes triplet symmetry even as an excited state; (2) superconductivity is substantially weakened by SF, but anisotropy remains as above; and, (3) we do find the possibility of a Leggett mode, not in a singlet–triplet but in an s ++ – s ± channel.
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- PAR ID:
- 10409103
- Date Published:
- Journal Name:
- npj Computational Materials
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2057-3960
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1038/s41524-023-01017-4
