Machine-learning predictions of positron binding to molecules

Amaral, Paulo H. R.; Mohallem, José R.

doi:10.1103/physreva.102.052808

Cited by 11 publications

(9 citation statements)

References 37 publications

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“…dictions of positron binding to molecules [15]. It may be worth noting that our ab initio prediction of a bound state for CH 2 F 2 with 𝜀 𝑏 = 0.2 meV concurs with the prediction of a 0.4 meV bound state by an earlier empirical model [1].…”

supporting

confidence: 85%

“…, where 𝜑 𝑖 is the 𝑖-th electron molecular orbital and 𝛾 𝑖 ≥ 1 are enhancement factors that account for an increased density of electrons at the positron due to short-range correlations. They are given by 15 , where 𝜀 𝑖 is the energy of molecular orbital 𝜑 𝑖 [29,30]. We found that for the chlorinated molecules the unenhanced and enhanced contact densities followed 𝛿 𝑒 𝑝 = (𝐹/2𝜋)𝜅, where 𝜅 = √ 2𝜀 𝑏 , and 𝐹 = 0.13 and 0.64 respectively (correlation coefficient 0.97 in both cases).…”

mentioning

confidence: 85%

“…Trap-based positron beams have enabled resonantannihilation-based measurements of positron binding energies to around 90 molecules over the last two decades (see e.g., [1][2][3][4][5]). Whilst the corresponding model of positron capture into vibrational Feshbach resonances is well established [6][7][8], progress in the accurate calculation of positron binding energies has only been made relatively recently (see e.g., [9][10][11][12][13][14][15][16]). Whilst attempts have been made to relate the observed binding energies to the coarse molecular properties including the dipole moment, polarizability and ionization potential [1,3,15], no universal formula has been established.…”

mentioning

confidence: 99%

“…Whilst the corresponding model of positron capture into vibrational Feshbach resonances is well established [6][7][8], progress in the accurate calculation of positron binding energies has only been made relatively recently (see e.g., [9][10][11][12][13][14][15][16]). Whilst attempts have been made to relate the observed binding energies to the coarse molecular properties including the dipole moment, polarizability and ionization potential [1,3,15], no universal formula has been established. Indeed, recently we developed a many-body theory (MBT) approach that quantified the role of strong many-body correlations, and beyond the interplay of the coarse properties, highlighted the importance of individual molecular orbital contributions to the positronmolecule potential, e.g., the enhancement of binding due to 𝜋 bonds [14,16] that has also been deduced from experiment [1,17,18].…”

mentioning

confidence: 99%

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Many-body Theory Calculations of Positron Binding to Halogenated Hydrocarbons

Cassidy¹,

Hofierka²,

Cunningham³

et al. 2023

Preprint

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Positron binding energies in halogenated hydrocarbons are calculated ab initio using many-body theory, elucidating the role of the anisotropic positron-molecule potential and the comparative effect of fluorination vs. chlorination. For chlorinated molecules, including planar molecules for which the interaction is highly anisotropic, excellent agreement with experiment and recent DFT-based model-potential calculations of [Suzuki et al., Phys. Rev. A 102, 052830 (2020)] is found. It is shown that their fluorinated counterparts generate a less attractive positron-molecule potential due to higher molecular orbital ionization energies and smaller density of occupied valence molecular orbitals, resulting in very weak, or in most cases loss of, positron binding.

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supporting

confidence: 85%

mentioning

confidence: 85%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Many-body Theory Calculations of Positron Binding to Halogenated Hydrocarbons

Cassidy¹,

Hofierka²,

Cunningham³

et al. 2023

Preprint

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“…Moreover, the strength of the short-range virtual-positronium process will depend on the ionisation energies I of the electrons in the molecule: less tightly bound electrons can more easily tunnel away from the molecule to the positron. Indeed, a more recent machine-learning based regression analysis of the experimental binding energies saw evidence that the binding was dependent on I, 55 though little fundamental insight was provided. For the molecules considered here, we find that there is a significant contribution to the correlation potential from a range of HOMOs (each with different I).…”

Section: Polar Moleculesmentioning

confidence: 99%

Many-body theory of positron binding in polyatomic molecules

Hofierka¹,

Cunningham²,

Rawlins³

et al. 2021

Preprint

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Positrons bind to molecules leading to vibrational excitation and spectacularly enhanced annihilation. 1 Whilst positron binding energies have been measured via resonant annihilation spectra for ∼ 80 molecules in the past two decades, [2][3][4][5][6][7][8][9][10][11][12] an accurate ab initio theoretical description has remained elusive. Of the molecules studied experimentally, calculations exist for only 6, and for these, standard quantum chemistry approaches have proved severely deficient, agreeing with experiment to at best 25% accuracy for polar molecules, and failing to predict binding in non-polar molecules. The theoretical difficulty lies in the need to accurately account for positron-molecule correlations including polarisation of the electron cloud, screening of the positron-molecule Coulomb interaction by molecular electrons, and the unique non-perturbative process of virtual-positronium formation (where a molecular electron temporarily tunnels to the positron). Their roles in positron-molecule binding have yet to be elucidated. Here, we develop a diagrammatic many-body description of positron-molecule interactions that takes ab initio account of the correlations, applying it to calculate positron binding energies for the molecules for which both theory and experimental results exist. Delineating the effects of the correlations, we find that in particular, virtual-positronium formation dramatically enhances binding in organic polar molecules, and can be essential to support binding in non-polar molecules. Overall, we find the best agreement with experiment to date (in some cases to within a few percent). The approach can be extended to provide predictive calculations of positron scattering and annihilation γ spectra in molecules and condensed matter. The fundamental insight provided by such capability is required to, e.g., develop antimatter-based technologies including positron traps, beams and positron emission tomography, properly interpret materials science diagnostic techniques, 13,14 and understand positrons in the galaxy. 15 Moreover, the positron-matter problem provides an unforgiving testbed for the development of computational methods to tackle the quantum many-body problem, for which our results can serve as benchmarks.Pioneering technological developments have enabled the trapping, accumulation and delivery 14,16,17 of positrons for study of their fundamental interactions with atoms and molecules, 1, 18 and the formation, exploitation and interrogation of more complicated antimatter, namely positronium (Ps), 19,20 and antihydrogen. 21 The ability of positrons to annihilate with atomic electrons forming characteristic γ rays make them a unique probe over vast length scales, giving them important use in e.g., materials science for ultra-sensitive diagnostics of industrially important materials and surface processes, 13, 14 positron emission tomography (PET) for functional medical imaging, 22 and in astrophysics. 15 Proper interpretation of the difficult and costly antimatter experiments and ma...

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Influence of geometry on positron binding to molecules

Danielson¹,

Ghosh²,

Surko³

2021

J. Phys. B: At. Mol. Opt. Phys.

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Annihilation studies have established that positrons bind to most molecules. They also provide measurements of the positron-molecule binding energies, which are found to vary widely and depend upon molecular size and composition. Trends of binding energy with global parameters such as molecular polarizability and dipole moment have been discussed previously. In this paper, the dependence of binding energy on molecular geometry is investigated by studying resonant positron annihilation on selected pairs of isomers. It is found that molecular geometry can play a significant role in determining the binding energies even for isomers with very similar polarizabilities and dipole moments. The possible origins of this dependence are discussed.

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Machine-learning predictions of positron binding to molecules

Cited by 11 publications

References 37 publications

Many-body Theory Calculations of Positron Binding to Halogenated Hydrocarbons

Many-body Theory Calculations of Positron Binding to Halogenated Hydrocarbons

Many-body theory of positron binding in polyatomic molecules

Influence of geometry on positron binding to molecules

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