Polaron pattern recognition
in correlated oxide surfaces
Subproject P07
The formation of polarons by charge trapping is pervasive in transition metal oxides. Polarons have been widely studied in binary compounds but comparatively much less so in perovskites.
In P07, we aim to combine advanced first-principles approaches with computer-vision and machine-learning techniques to accelerate and automatize the study of polarons and novel polaron effects in perovskites.
The project has three main pillars: (i) artificial intelligence-aided analysis of experimental ncAFM/STM results (from P02 Diebold, P04 Parkinson) to extract lattice symmetry, surface structure, and chemical composition; (ii) calculation of polaronic configurational energies at different concentrations and temperature using NN; and (iii) identification of unusual types of polarons and polaron-defect complexes in doped perovskites such as spin-, ferroelectric-, Jahn-Teller-, small polarons, and bipolarons.
In the long-term, we plan to establish a fully automatic diagnosis of ncAFM/STM (symmetry, defects, domains) and LEED (diffraction, surface reconstruction) and the construction of a combined experiment & theory database. The research will benefit from two external collaborators and synergy with several experimental (P02, P04) and computational (P03 Kresse, P09 Madsen) TACO partners.
Expertise
Theoretical and computational modeling of quantum materials, in particular transition metal oxides in bulk phases and surfaces, to predict and interpret novel physical effects and states of matter arising from fundamental quantum interactions: electron-electron correlation, electron-phonon coupling, spin-spin exchange, spin-orbit coupling, to name the most relevant ones. The theoretical research is conducted in strong synergy and cooperation with experimental groups.
Methods:
- Density functional theory, hybrid functionals, GW, BSE
- First principles molecular dynamics
- Effective Hamiltonian
- Diagrammatic quantum Monte Carlo
- Dynamical mean-field theory
- Machine learning and computer vision
Applications:
- Polarons: formation, dynamics, polaron-mediated effects, many-body properties
- Computational surface science: energetics, reconstructions, surface polarons, polarity effects, adsorption and chemical reactions
- Quantum magnetism: all-rank multipolar spin-spin interactions beyond Heisenberg exchange
- Electronic and magnetic phase transitions
Our goals in TACO:
- Accelerated study of polaron properties by integrating molecular dynamics and machine learning methods (kernel-ridge regression, standard and convolutional neural-networks
- Implementation of automated identification of local structures in atomically resolved images using computer vision methods
- Complementing the experimental measurements with extensive first principles modeling of perovskite surfaces.
Team

Publications
2022

Meier, Matthias; Hulva, Jan; Jakub, Zdenek; Kraushofer, Florian; Bobić, Mislav; Bliem, Roland; Setvin, Martin; Schmid, Michael; Diebold, Ulrike; Franchini, Cesare; Parkinson, Gareth S.
Journal ArticleOpen AccessIn: Science Advances, vol. 8, iss. 13, pp. eabn4580, 2022.
Abstract | Links | BibTeX | Tags: P02, P04, P07
@article{SCIADV2022,
title = {CO oxidation by Pt_{2}/Fe_{3}O_{4}: Metastable dimer and support configurations facilitate lattice oxygen extraction},
author = {Matthias Meier and Jan Hulva and Zdenek Jakub and Florian Kraushofer and Mislav Bobić and Roland Bliem and Martin Setvin and Michael Schmid and Ulrike Diebold and Cesare Franchini and Gareth S. Parkinson},
url = {https://www.science.org/doi/10.1126/sciadv.abn4580},
doi = {10.1126/sciadv.abn4580},
year = {2022},
date = {2022-04-01},
urldate = {2022-04-01},
journal = {Science Advances},
volume = {8},
issue = {13},
pages = {eabn4580},
abstract = {Heterogeneous catalysts based on subnanometer metal clusters often exhibit strongly size-dependent properties, and the addition or removal of a single atom can make all the difference. Identifying the most active species and deciphering the reaction mechanism is extremely difficult, however, because it is often not clear how the catalyst evolves in operando. Here, we use a combination of atomically resolved scanning probe microscopies, spectroscopic techniques, and density functional theory (DFT)–based calculations to study CO oxidation by a model Pt/Fe_{3}O_{4}(001) “single-atom” catalyst. We demonstrate that (PtCO)_{2} dimers, formed dynamically through the agglomeration of mobile Pt-carbonyl species, catalyze a reaction involving the oxide support to form CO_{2}. Pt_{2} dimers produce one CO_{2} molecule before falling apart into two adatoms, releasing the second CO. Olattice extraction only becomes facile when both the Pt-dimer and the Fe_{3}O_{4} support can access metastable configurations, suggesting that substantial, concerted rearrangements of both cluster and support must be considered for reactions occurring at elevated temperature.},
keywords = {P02, P04, P07},
pubstate = {published},
tppubtype = {article}
}

Reticcioli, Michele; Diebold, Ulrike; Franchini, Cesare
Modeling polarons in density functional theory: lessons learned from TiO2
Journal ArticleOpen AccessIn: Journal of Physics: Condensed Matter, vol. 34, no. 20, pp. 204006, 2022.
Abstract | Links | BibTeX | Tags: P02, P07
@article{JPCM2022,
title = {Modeling polarons in density functional theory: lessons learned from TiO_{2}},
author = {Michele Reticcioli and Ulrike Diebold and Cesare Franchini},
url = {https://iopscience.iop.org/article/10.1088/1361-648X/ac58d7},
doi = {10.1088/1361-648X/ac58d7},
year = {2022},
date = {2022-03-14},
urldate = {2022-03-14},
journal = {Journal of Physics: Condensed Matter},
volume = {34},
number = {20},
pages = {204006},
abstract = {Density functional theory (DFT) is nowadays one of the most broadly used and successful techniques to study the properties of polarons and their effects in materials. Here, we systematically analyze the aspects of the theoretical calculations that are crucial to obtain reliable predictions in agreement with the experimental observations. We focus on rutile TiO_{2}, a prototypical polaronic compound, and compare the formation of polarons on the (110) surface and subsurface atomic layers. As expected, the parameter U used to correct the electronic correlation in the DFT+U formalism affects the resulting charge localization, local structural distortions and electronic properties of polarons. Moreover, the polaron localization can be driven to different sites by strain: Due to different local environments, surface and subsurface polarons show different responses to the applied strain, with impact on the relative energy stability. An accurate description of the properties of polarons is key to understand their impact on complex phenomena and applications: As an example, we show the effects of lattice strain on the interaction between polarons and CO adsorbates.},
keywords = {P02, P07},
pubstate = {published},
tppubtype = {article}
}
2021
Jakub, Zdenek; Meier, Matthias; Kraushofer, Florian; Balajka, Jan; Pavelec, Jiri; Schmid, Michael; Franchini, Cesare; Diebold, Ulrike; Parkinson, Gareth S.
Rapid oxygen exchange between hematite and water vapor
Journal ArticleOpen AccessIn: Nature Communications, vol. 12, iss. 1, no. 6488, 2021.
Abstract | Links | BibTeX | Tags: P02, P04, P07
@article{Jakub2021,
title = {Rapid oxygen exchange between hematite and water vapor},
author = {Zdenek Jakub and Matthias Meier and Florian Kraushofer and Jan Balajka and Jiri Pavelec and Michael Schmid and Cesare Franchini and Ulrike Diebold and Gareth S. Parkinson},
doi = {10.1038/s41467-021-26601-4},
year = {2021},
date = {2021-11-10},
journal = {Nature Communications},
volume = {12},
number = {6488},
issue = {1},
publisher = {Springer Science and Business Media LLC},
abstract = {Oxygen exchange at oxide/liquid and oxide/gas interfaces is important in technology and environmental studies, as it is closely linked to both catalytic activity and material degradation. The atomic-scale details are mostly unknown, however, and are often ascribed to poorly defined defects in the crystal lattice. Here we show that even thermodynamically stable, well-ordered surfaces can be surprisingly reactive. Specifically, we show that all the 3-fold coordinated lattice oxygen atoms on a defect-free single-crystalline “r-cut” (1-102) surface of hematite (α-Fe_{2}O_{3}) are exchanged with oxygen from surrounding water vapor within minutes at temperatures below 70 °C, while the atomic-scale surface structure is unperturbed by the process. A similar behavior is observed after liquid-water exposure, but the experimental data clearly show most of the exchange happens during desorption of the final monolayer, not during immersion. Density functional theory computations show that the exchange can happen during on-surface diffusion, where the cost of the lattice oxygen extraction is compensated by the stability of an HO-HOH-OH complex. Such insights into lattice oxygen stability are highly relevant for many research fields ranging from catalysis and hydrogen production to geochemistry and paleoclimatology.},
keywords = {P02, P04, P07},
pubstate = {published},
tppubtype = {article}
}