The Muon Spectroscopy Computational Project

Publications

• Exploring the Temperature Dependent Solid-State ALC Spectrum of the C₆H₆Mu^• Radical with Ab-Initio Simulation Techniques
  JPS Conf. Proc. 21, 011036, (2018)
  In this work, we used a number of different computational techniques to study the temperature dependence of the Avoided Level Crossing spectrum of crystalline benzene.

• Computational Prediction of Muon Stopping Sites Using AIRSS
  The Journal of Chemical Physics, 148, 134114, (2018)
  The stopping site of the muon in a muon-spin relaxation experiment (µ+SR) is generally unknown and there few techniques that can be used to determine the muon stopping site. In this work, we propose a purely theoretical method that can be used to predict muon stopping sites in crystalline materials using only computer simulations.

• Comparison between Density Functional Theory and Density Functional Tight Binding approaches for finding the muon stopping site in organic molecular crystals
  The Journal of Chemical Physics, 150, 154301, (2019)
  Expanding on our previous use of AIRSS to find the muon stopping site, this paper focuses on its application to organic molecules and shows how the tight binding software DFTB+, combined with the 3ob-3-1 parameter set, can produce satisfying results for it in a fraction of the time required by DFT simulations.

• A Muon Spectroscopic and Computational Study of the Microscopic Electronic Structure in Thermoelectric Hybrid Silicon Nanostructures
  J. Phys. Chem. C, 124, 18, 9656–9664, (2020)
  Phenylacetylene-capped silicon nanoparticles have attracted interest as a novel thermoelectric material. In this paper, we report a combined muon spectroscopic (μSR) and computational study of this material in solution to investigate the microscopic electronic structure of this system.

• Computational prediction of muon stopping sites: A novel take on the unperturbed electrostatic potential method
  The Journal of Chemical Physics, 153, 044111, (2020)
  In this work, we present a software implementation of the Unperturbed Electrostatic Potential (UEP) Method: an approach used for finding the muon stopping site in crystalline materials. The UEP method requires only one DFT calculation, necessary to compute the electronic density of the host material.

• Mudirac: A Dirac equation solver for elemental analysis with muonic X‐rays
  X-Ray Spectrometry,1–17, (2020)
  In this work, we present mudirac: a new open‐source software for the integration of the radial Dirac equation developed specifically for muonic atoms. The software can be used to predict frequencies and transitions probabilities between levels of the muonic atom, which are useful for the interpretation of muonic X‐ray spectra in elemental analysis.

• Observation of a molecular muonium polaron and its application to probing magnetic and electronic states
  Phys.Rev.B 104,064429, (2021)
  Here, we give evidence for the detection of a muonium state that propagates in a molecular semiconductor lattice via thermally activated dynamics: a muonium polaron.

• Low-temperature magnetic crossover in the topological kagome magnet TbMn₆Sn₆
  Communications Physics volume 5, Article number: 107, (2022)
  Here, we explore magnetic correlations in the recently identified topological kagome system TbMn₆Sn₆ using muon spin rotation, combined with local field analysis and neutron diffraction. Our studies identify an out-of-plane ferrimagnetic structure with slow magnetic fluctuations which exhibit a critical slowing down below T^*_C1 ≃ 120 K and finally freeze into static patches with ideal out-of-plane order below T_C1 ≃ 20 K.

• MuSpinSim: spin dynamics calculations for muon science
  J. Phys.: Conf. Ser. 2462 012017, (2023)
  In this work, we present muspinsim: an open-source python package to simulate the spin dynamics of a system of a muon along with other spins such as electrons and atomic nuclei. All of its utilities to facilitate µSR experiments are also detailed.

• Magnetic structure and crystal field states of Pr₂Pd₃Ge₅: μSR and neutron scattering investigations
  Phys.Rev.B 107,104412, (2023)
  In this work, we present the results of muon spin relaxation (μSR), powder neutron diffraction, and inelastic neutron scattering investigations on polycrystalline Pr₂Pd₃Ge₅. The material exhibits dual antiferromagnetic transitions, confirmed by heat capacity measurements. Our findings reveal a canted antiferromagnetic structure of ordered Pr³⁺ moments. The internal field calculations at muon stopping sites predicted by DFT calculation are in good agreement with experimental observations. In the paramagnetic state, 3 crystal electric field excitations were identified arising from the crystal electric field split J=4 ground state of Pr³⁺.

• Hidden magnetism uncovered in a charge ordered bilayer kagome material ScV₆Sn₆
  Nat Commun 14, 7796, (2023)
  Here, we present the discovery of an unnexpected hidden magnetism of the charge orger for the recently discovered charge ordered kagome material - ScV₆Sn₆ using advanced muon-spin rotation spectroscopy. An enhancement was observed in the internal field width sensed by the muon ensemble, which takes place within the charge ordered state. Furthermore, the muon spin relaxation rate below the charge ordering temperature is substantially enhanced by applying an external magnetic field. Taken together with the hidden magnetism found in AV₃Sb₅ (A = K, Rb, Cs) and FeGe kagome systems, our results suggest ubiqitous time-reversal symmetry-breaking in charge ordered kagome lattices.

Selected Presentations

• Computational Prediction of Muon Stopping Sites in Silicon
  The 14th International Conference on Muon Spin Rotation, Relaxation and Resonance. 30 June 2017, Sapporo, Japan.
  This work focuses on the paramagnetic states formed by muons in semiconductors. In particular, it revisits the case of muons in pure Si, and uses a combination of computational methods to estimate the muon stopping sites.

• Computer Simulations for Interpreting µSR Experiments: Beyond DFT
  Muon Spectroscopy User Meeting: Future Developments and Site Calculations. 17 July 2018, The Cosener’s House, Abingdon, UK.
  This presentation discusses the computational methods that we had developed so far to estimate the muon stopping site in crystalline materials. The key new concept is the development of methods based on calculations other than ab-initio calculations. The idea is that the new calculations are computationally faster than the purely ab initio ones. One of the methods that I have tested is the DFT-based Tight-Binding.

• CalcALC: a user tool for predicting and interpreting ALC and QLCR spectra
  Muon Spectroscopy User Meeting: Future Developments and Site Calculations. 17 July 2018, The Cosener’s House, Abingdon, UK.\

• Computer Simulations for Interpreting μSR Experiments
  The 2018 ISIS Muon Spectroscopy Training School. 22 March 2018, Rutherford Appleton Laboratory, Harwell, UK.
  This talk presents the key concepts and the main approximations used in our computer models, and also discusses why some of these approximations are relevant to muon experiments. In particular, there is a brief introduction to Density Functional Theory (DFT) and how it can be used to study muonated molecular and crystalline systems. This talk also presents the basis for the method that we are developing to predict the muon stopping sites in crystalline materials.

• Computer Simulations for Interpreting μSR Experiments
  International Advanced School on Muon Spectroscopy. 15-22 August 2019, Rutherford Appleton Laboratory, Harwell, UK.
  This talk presents the key concepts and the main approximations used in our computer models. The talk discusses Density Functional Theory (DFT), briefly presents some of the current codes that implement DFT and how these different codes can be used to study muonated crystalline systems. In particular, the talk presents all the methods that we developed to predict the muon stopping site in crystalline systems.

• The Ada Lovelace Project on Muon Spectroscopy
  2020 Edition Muon Site Calculation Meeting (Virtual Edition). 4 September, 2020.
  In this talk, we presented the work that we are doing -and plan to do- as part of a grant that we obtained from Ada Lovelace Centre for the development of muon software. The main objective of this grant is the development of a sustainable and user-friendly software platform that can be used for developing software for interpreting muon experiments.

• Scientific Computing for Muons: the Muon Spectroscopy Computational Project
  Muon Jamboree! (Virtual Edition). 13-16 December, 2021.
  In this talk, we presented the Muon Spectrocopy Computational Project to the worlwide muon community.

• Muon Galaxy: Extending Galaxy for Muon Science
  Galaxy Community Conference 2021 (Virtual Edition). 28 June - 10 July, 2021.
  In this talk, we presented our newly developed Galaxy instance, Muon Galaxy, to the global Galaxy community.

• MuSpinSim: spin dynamics calculations for muon science
  15th International Conference on Muon Spin Rotation, Relaxation and Resonance. 28 August - 2 September, 2022.
  In this talk, we presented our MuSpinSim, the latest addition to the MSCP, to the global muon community.

• Muon Galaxy: Facilitating FAIR data analysis in muon science
  RSECon 2022. 6-8 September, 2022.
  In this talk, we presented a full version of Muon Galaxy and stressed its capabilities to perform FAIR analysis in muon science.

• Muon Galaxy – an open web platform for computational muon science
  NOBUGS 2022. 19-22 September, 2022.
  The goal of the NOBUGS (New Opportunities for Better User Group Software) Conference Series is to foster collaboration and exchange between scientists and IT professionals working on software for X-ray, neutron and muon sources from around the world. We presented Muon Galaxy to this community.

• Galaxy and Scientific Communities: How to Incorporate New Ones, Uplift Engaged Ones and Maintain Mature Ones​
  THE PASC23 CONFERENCE 2023. 26-28 June, 2023.
  The goal of the Platform for Advanced Scientific Computing (PASC) Conference for 2023 focusses on advances in aggregating, synthesizing, and transitioning across scales, domains, and communities. We presented the capabilites of the Galaxy platform and its specific use in Muon Science and Astrophysics.

• Computing Simulations for Large Scale Experiments: the Case of Muons​
  Presentation to the Catalysis Hub. 18 July, 2023, Harwell, UK.\

• Computational Techniques to Support Muon Science: the Muon Spectroscopy Computational Project at ISIS
  Japan Proton Accelerator Research Complex (J-PARC). 4 August, 2023.\

• Finding the Muon Stopping Site: pymuon-suite in​ Galaxy​
  Muon User Meeting 2023: celebrating the work of Pabitra Biswas. 11-12 September, 2023, The Queens College, Oxford, UK.\

• Applications to Catalysis Workflows​
  European Galaxy Days (EGD). 4-6 October, 2023, Freiburg, Germany.\

• Galaxy workflow tools for processing and analysis of catalysis data (Short Lecture)​
  Presentation to the Catalysis Hub. 2 November, 2023, Harwell, UK.\

• Galaxy workflow tools for processing and analysis of catalysis data (Flash Pitch)
  Presentation to the Catalysis Hub. 2 November, 2023, Harwell, UK.\

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