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Cassella G, Foulkes WMC, Pfau D, Spencer JS. Neural network variational Monte Carlo for positronic chemistry. Nat Commun 2024; 15:5214. [PMID: 38890287 PMCID: PMC11189582 DOI: 10.1038/s41467-024-49290-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Accepted: 05/29/2024] [Indexed: 06/20/2024] Open
Abstract
Quantum chemical calculations of the ground-state properties of positron-molecule complexes are challenging. The main difficulty lies in employing an appropriate basis set for representing the coalescence between electrons and a positron. Here, we tackle this problem with the recently developed Fermionic neural network (FermiNet) wavefunction, which does not depend on a basis set. We find that FermiNet produces highly accurate, in some cases state-of-the-art, ground-state energies across a range of atoms and small molecules with a wide variety of qualitatively distinct positron binding characteristics. We calculate the binding energy of the challenging non-polar benzene molecule, finding good agreement with the experimental value, and obtain annihilation rates which compare favourably with those obtained with explicitly correlated Gaussian wavefunctions. Our results demonstrate a generic advantage of neural network wavefunction-based methods and broaden their applicability to systems beyond the standard molecular Hamiltonian.
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Affiliation(s)
- Gino Cassella
- Dept. of Physics, Imperial College London, London, SW7 2AZ, UK.
| | - W M C Foulkes
- Dept. of Physics, Imperial College London, London, SW7 2AZ, UK
| | - David Pfau
- Dept. of Physics, Imperial College London, London, SW7 2AZ, UK
- DeepMind, London, N1C 4DJ, UK
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Cassidy JP, Hofierka J, Cunningham B, Green DG. Many-body theory calculations of positronic-bonded molecular dianions. J Chem Phys 2024; 160:084304. [PMID: 38407288 DOI: 10.1063/5.0188719] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2023] [Accepted: 01/26/2024] [Indexed: 02/27/2024] Open
Abstract
The energetic stability of positron-dianion systems [A-; e+; A-] is studied via many-body theory, where A- includes H-, F-, Cl-, and the molecular anions (CN)- and (NCO)-. Specifically, the energy of the system as a function of ionic separation is determined by solving the Dyson equation for the positron in the field of the two anions using a positron-anion self-energy as constructed in Hofierka et al. [Nature 606, 688 (2022)] that accounts for correlations, including polarization, screening, and virtual-positronium formation. Calculations are performed for a positron interacting with H22-, F22-, and Cl22- and are found to be in good agreement with previous theory. In particular, we confirm the presence of two minima in the potential energy of the [H-; e+; H-] system with respect to ionic separation: a positronically bonded [H-; e+; H-] local minimum at ionic separations r ∼ 3.4 Å and a global minimum at smaller ionic separations r ≲ 1.6 Å that gives overall instability of the system with respect to dissociation into a H2 molecule and a positronium negative ion, Ps-. The first predictions are made for positronic bonding in dianions consisting of molecular anionic fragments, specifically for (CN)22- and (NCO)22-. In all cases, we find that the molecules formed by the creation of a positronic bond are stable relative to dissociation into A- and e+A- (positron bound to a single anion), with bond energies on the order of 1 eV and bond lengths on the order of several ångstroms.
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Affiliation(s)
- J P Cassidy
- Centre for Light-Matter Interactions, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdom
| | - J Hofierka
- Centre for Light-Matter Interactions, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdom
| | - B Cunningham
- Centre for Light-Matter Interactions, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdom
| | - D G Green
- Centre for Light-Matter Interactions, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdom
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Goli M, Bressanini D, Shahbazian S. On the nature of the two-positron bond: evidence for a novel bond type. Phys Chem Chem Phys 2023; 25:29531-29547. [PMID: 37905569 DOI: 10.1039/d3cp03003b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2023]
Abstract
The nature of the newly proposed two-positron bond in (PsH)2, which is composed of two protons, four electrons and two positrons, is considered in this contribution. The study is done at the multi-component-Hartree-Fock (MC-HF) and the Diffusion Monte Carlo (DMC) levels of theory by comparing ab initio data, analyzing the spatial structure of the DMC wavefunction, and applying the multi-component quantum theory of atoms in molecules and the two-component interacting quantum atoms energy partitioning schemes to the MC-HF wavefunction. The analysis demonstrates that (PsH)2 to a good approximation may be conceived of as two slightly perturbed PsH atoms, bonded through a two-positron bond. In contrast to the usual two-electron bonds, the positron exchange phenomenon is quite marginal in the considered two-positron bond. The dominant stabilizing mechanism of bonding is a novel type of classical electrostatic interaction between the positrons, which are mainly localized between nuclei, and the surrounding electrons. To emphasize its uniqueness, this mechanism of bonding is proposed to be called gluonic which has also been previously identified as the main driving mechanism behind formation of the one-positron bond in [H-,e+,H-]. We conclude that the studied two-positron bond should not be classified as a covalent bond and it must be seen as a brand-new type of bond, foreign to the electronic bonding modes discovered so far in the purely electronic systems.
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Affiliation(s)
- Mohammad Goli
- School of Nano Science, Institute for Research in Fundamental Sciences (IPM), Tehran 19395-5531, Iran.
| | - Dario Bressanini
- Dipartimento di Scienza e Alta Tecnologia, Università dell'Insubria, Como, Italy.
| | - Shant Shahbazian
- Department of Physics, Shahid Beheshti University, Evin, Tehran 19839-69411, Iran.
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Tachibana T, Hoshi D, Nagashima Y. Molecular Ion Desorption from LiF(110) Surfaces by Positron Annihilation. PHYSICAL REVIEW LETTERS 2023; 131:143201. [PMID: 37862658 DOI: 10.1103/physrevlett.131.143201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Revised: 09/02/2023] [Accepted: 09/11/2023] [Indexed: 10/22/2023]
Abstract
We have studied the desorption of positive ions from a LiF(110) crystal surface using positron and electron irradiation at 500 eV to examine the interaction between positrons and ionic crystals. Only monatomic ions, such as H^{+}, Li^{+}, and F^{+}, are detected under electron irradiation. However, positron irradiation leads to the significant desorption of ionic molecules, specifically, FH^{+} and F_{2}^{+}. Molecular ion yields are more sensitive to temperature than atomic ion yields. Based on the findings, we propose a desorption model in which positronic compounds are initially produced at the surface and subsequently desorbed as molecular ions via Auger decay following positron annihilation.
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Affiliation(s)
- T Tachibana
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
| | - D Hoshi
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
| | - Y Nagashima
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
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Charry J, Moncada F, Barborini M, Pedraza-González L, Varella MTDN, Tkatchenko A, Reyes A. The three-center two-positron bond. Chem Sci 2022; 13:13795-13802. [PMID: 36544737 PMCID: PMC9710307 DOI: 10.1039/d2sc04630j] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Accepted: 10/16/2022] [Indexed: 12/24/2022] Open
Abstract
Computational studies have shown that one or more positrons can stabilize two repelling atomic anions through the formation of two-center positronic bonds. In the present work, we study the energetic stability of a system containing two positrons and three hydride anions, namely 2e+[H3 3-]. To this aim, we performed a preliminary scan of the potential energy surface of the system with both electrons and positrons in a spin singlet state, with a multi-component MP2 method, that was further refined with variational and diffusion Monte Carlo calculations, and confirmed an equilibrium geometry with D 3h symmetry. The local stability of 2e+[H3 3-] is demonstrated by analyzing the vertical detachment and adiabatic energy dissociation channels. Bonding properties of the positronic compound, such as the equilibrium interatomic distances, force constants, dissociation energies, and bonding densities are compared with those of the purely electronic H3 + and Li3 + systems. Through this analysis, we find compelling similarities between the 2e+[H3 3-] compound and the trilithium cation. Our results strongly point out the formation of a non-electronic three-center two-positron bond, analogous to the well-known three-center two-electron counterparts, which is fundamentally distinct from the two-center two-positron bond [D. Bressanini, J. Chem. Phys., 2021, 155, 054306], thus extending the concept of positron bonded molecules.
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Affiliation(s)
- Jorge Charry
- Department of Physics and Materials Science, University of LuxembourgL-1511 Luxembourg CityLuxembourg
| | - Félix Moncada
- Department of Physics, AlbaNova University Center, Stockholm UniversityS-106 91 StockholmSweden,Department of Chemistry, Universidad Nacional de ColombiaAv. Cra 30 #45-03BogotáColombia
| | - Matteo Barborini
- Department of Physics and Materials Science, University of LuxembourgL-1511 Luxembourg CityLuxembourg
| | - Laura Pedraza-González
- Department of Chemistry and Industrial Chemistry, University of PisaVia Moruzzi 1356124PisaItaly
| | - Márcio T. do N. Varella
- Instituto de Física, Universidade de São PauloRua do Matão 1731São PauloSão Paulo05508-090Brazil
| | - Alexandre Tkatchenko
- Department of Physics and Materials Science, University of LuxembourgL-1511 Luxembourg CityLuxembourg
| | - Andrés Reyes
- Department of Chemistry, Universidad Nacional de ColombiaAv. Cra 30 #45-03BogotáColombia
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Charry Martinez J, Barborini M, Tkatchenko A. Correlated Wave Functions for Electron-Positron Interactions in Atoms and Molecules. J Chem Theory Comput 2022; 18:2267-2280. [PMID: 35333513 PMCID: PMC9009097 DOI: 10.1021/acs.jctc.1c01193] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Indexed: 11/29/2022]
Abstract
The positron, as the antiparticle of the electron, can form metastable states with atoms and molecules before its annihilation with an electron. Such metastable matter-positron complexes are stabilized by a variety of mechanisms, which can have both covalent and noncovalent character. Specifically, electron-positron binding often involves strong many-body correlation effects, posing a substantial challenge for quantum-chemical methods based on atomic orbitals. Here we propose an accurate, efficient, and transferable variational ansatz based on a combination of electron-positron geminal orbitals and a Jastrow factor that explicitly includes the electron-positron correlations in the field of the nuclei, which are optimized at the level of variational Monte Carlo (VMC). We apply this approach in combination with diffusion Monte Carlo (DMC) to calculate binding energies for a positron e+ and a positronium Ps (the pseudoatomic electron-positron pair), bound to a set of atomic systems (H-, Li+, Li, Li-, Be+, Be, B-, C-, O- and F-). For PsB, PsC, PsO, and PsF, our VMC and DMC total energies are lower than that from previous calculations; hence, we redefine the state of the art for these systems. To assess our approach for molecules, we study the potential-energy surfaces (PES) of two hydrogen anions H- mediated by a positron (e+H22-), for which we calculate accurate spectroscopic properties by using a dense interpolation of the PES. We demonstrate the reliability and transferability of our correlated wave functions for electron-positron interactions with respect to state-of-the-art calculations reported in the literature.
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Affiliation(s)
| | - Matteo Barborini
- Department of Physics and Materials
Science, University of Luxembourg, L-1511, Luxembourg
City, Luxembourg
| | - Alexandre Tkatchenko
- Department of Physics and Materials
Science, University of Luxembourg, L-1511, Luxembourg
City, Luxembourg
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Bressanini D. e+(PsH)2: a three-positron molecule with a positronic chemical bond. J Chem Phys 2022; 156:154302. [DOI: 10.1063/5.0089157] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Two new positronic molecules have been recently discovered: [Angew. Chem. Int. Ed. 57, 8859-8864 (2018)] and (PsH)2 [J. Chem. Phys. 155, 054306 (2021)]. These molecules seem to be stabilized by a new type of bond, the positronic bond, where one or two positrons are directly responsible for the bonding of two otherwise repelling negative ions. We show that a positron can attach to (PsH)2 to form a locally stable species with three positrons whose potential energy curve shows an equilibrium structure at about 8 bohr and a binding energy of 11.5(5) mhartree with respect to the dissociation into PsH + e+PsH. This molecule, tentatively called e+(PsH)2, is the first system with three positrons discovered.
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Affiliation(s)
- Dario Bressanini
- Dipartimento di Scienza e Alta Tecnologia, University of Insubria Department of Science and High Technology, Italy
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Abstract
We show that two positrons can form a chemical bond between two otherwise repelling ions, similar to what happens to two hydrogen atoms forming a hydrogen molecule. Two positronium hydride atoms (PsH) can form the stable species (PsH)2 when the two coupled positrons have opposite spins, while they form an antibonding state if they have the same spin. This is completely analogous to the landmark description by Heitler and London [Z. Phys. 44, 455 (1927)] on the formation of a chemical bond in the hydrogen molecule coupling two electrons with opposite spins. This is the first time two positrons are shown to behave like two electrons in ordinary matter, enlarging the definition of what is a chemical bond dating back to Lewis [J. Am. Chem. Soc. 38, 762 (1916)]. We suggest a few experimental routes to form and detect such a peculiar molecule.
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Affiliation(s)
- Dario Bressanini
- Dipartimento di Scienza e Alta Tecnologia, Università dell'Insubria, Via Valleggio 9, I-22100 Como, Italy
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Abstract
The recently discovered positronic molecule e+H- 2 [J. Charry et al., Angew. Chem., Int. Ed. 57, 8859-8864 (2018)] has a new type of bond, the single-positron bond. We studied its stability using quantum Monte Carlo techniques. We computed an accurate potential energy curve of the reaction H- + PsH → e+H- 2 → H2 + Ps- to establish its global stability with respect to all possible dissociation channels and to define the range of its local stability. We showed that the e+H- 2 system is stable with respect to the dissociation into H- + PsH, with a binding energy of 23.5(1) mhartree. For R < 3.2 bohrs, the system is unstable, and it decays into H2 + Ps-. There are no other bound structures for R < 3.2 bohrs. We discuss possible routes to its experimental production.
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Affiliation(s)
- Dario Bressanini
- Dipartimento di Scienza e Alta Tecnologia, Università dell'Insubria, Via Valleggio 9, I-22100 Como, Italy
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Morales-Silva MA, Jordan KD, Shulenburger L, Wagner LK. Frontiers of stochastic electronic structure calculations. J Chem Phys 2021; 154:170401. [PMID: 34241059 DOI: 10.1063/5.0053674] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In recent years there has been a rapid growth in the development and application of new stochastic methods in electronic structure. These methods are quite diverse, from many-body wave function techniques in real space or determinant space to being used to sum perturbative expansions. This growth has been spurred by the more favorable scaling with the number of electrons and often better parallelization over large numbers of central processing unit (CPU) cores or graphical processing units (GPUs) than for high-end non-stochastic wave function based methods. This special issue of the Journal of Chemical Physics includes 33 papers that describe recent developments and applications in this area. As seen from the articles in the issue, stochastic electronic structure methods are applicable to both molecules and solids and can accurately describe systems with strong electron correlation. This issue was motivated, in part, by the 2019 Telluride Science Research Center workshop on Stochastic Electronic Structure Methods that we organized. Below we briefly describe each of the papers in the special issue, dividing the papers into six subtopics.
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Affiliation(s)
- Miguel A Morales-Silva
- Quantum Simulations Group, Lawrence Livermore National Laboratory, Livermore, California 94551, USA
| | - Kenneth D Jordan
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
| | - Luke Shulenburger
- HEDP Theory Department, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
| | - Lucas K Wagner
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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