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
2016
Wolfbeisser, Astrid; Sophiphun, Onsulang; Bernardi, Johannes; Wittayakun, Jatuporn; Föttinger, Karin; Rupprechter, Günther
Methane dry reforming over ceria-zirconia supported Ni catalysts
Journal ArticleOpen AccessIn: Catalysis Today, vol. 277, pp. 234–245, 2016.
Abstract | Links | BibTeX | Tags: P08, P10, pre-TACO
@article{Wolfbeisser2016,
title = {Methane dry reforming over ceria-zirconia supported Ni catalysts},
author = {Astrid Wolfbeisser and Onsulang Sophiphun and Johannes Bernardi and Jatuporn Wittayakun and Karin Föttinger and Günther Rupprechter},
doi = {10.1016/j.cattod.2016.04.025},
year = {2016},
date = {2016-11-15},
urldate = {2016-11-15},
journal = {Catalysis Today},
volume = {277},
pages = {234--245},
publisher = {Elsevier BV},
abstract = {Nickel nanoparticles supported on Ce_{1-x}Zr_{x}O_{2} mixed oxides prepared by different synthesis methods, as well as Ni-ZrO_{2} and Ni-CeO_{2}, were evaluated for their catalytic performance in methane dry reforming (MDR). MDR is an interesting model reaction to evaluate the reactivity and surface chemistry of mixed oxides. Textural and structural properties were studied by N_{2} adsorption and XRD. Mixed oxide preparation by co-precipitation resulted in catalysts with higher surface area than that of pure ZrO_{2} or CeO_{2}. XRD analysis showed the formation of different Ce_{1-x}Zr_{x}O_{2} solid solutions depending on using a surfactant or not. The catalyst prepared by surfactant assisted co-precipitation was not active for methane dry reforming most likely because of the encapsulation of Ni particles by ceria-zirconia particles, as revealed by TEM and H_{2} chemisorption. The catalytic activity of the catalyst prepared by co-precipitation without surfactant was comparable to Ni-ZrO_{2}. Clearly, catalyst activity strongly depends on preparation and on the resulting phase composition rather than on nominal composition. Compared to Ni-ZrO_{2} the ceria-zirconia supported Ni catalyst did not achieve higher activity or stability for methane dry reforming but, nevertheless, the formation of filamentous carbon was strongly reduced (100 times less carbonaceous species). Consequently, using ceria-zirconia as a support material decreases the risk of reactor tube blocking.},
keywords = {P08, P10, pre-TACO},
pubstate = {published},
tppubtype = {article}
}
van Roekeghem, Ambroise; Carrete, Jesús; Oses, Corey; Curtarolo, Stefano; Mingo, Natalio
Journal ArticleOpen AccessIn: Physical Review X, vol. 6, no. 4, pp. 041061, 2016.
Abstract | Links | BibTeX | Tags: P09, pre-TACO
@article{Roekeghem2016,
title = {High-Throughput Computation of Thermal Conductivity of High-Temperature Solid Phases: The Case of Oxide and Fluoride Perovskites},
author = {Ambroise van Roekeghem and Jesús Carrete and Corey Oses and Stefano Curtarolo and Natalio Mingo},
doi = {10.1103/physrevx.6.041061},
year = {2016},
date = {2016-06-13},
urldate = {2016-06-13},
journal = {Physical Review X},
volume = {6},
number = {4},
pages = {041061},
publisher = {American Physical Society (APS)},
abstract = {Using finite-temperature phonon calculations and machine-learning methods, we assess the mechanical stability of about 400 semiconducting oxides and fluorides with cubic perovskite structures at 0, 300, and 1000 K. We find 92 mechanically stable compounds at high temperatures—including 36 not mentioned in the literature so far—for which we calculate the thermal conductivity. We show that the thermal conductivity is generally smaller in fluorides than in oxides, largely due to a lower ionic charge, and describe simple structural descriptors that are correlated with its magnitude. Furthermore, we show that the thermal conductivities of most cubic perovskites decrease more slowly than the usual T^{−1} behavior. Within this set, we also screen for materials exhibiting negative thermal expansion. Finally, we describe a strategy to accelerate the discovery of mechanically stable compounds at high temperatures.},
keywords = {P09, pre-TACO},
pubstate = {published},
tppubtype = {article}
}
2014
Föttinger, Karin; Rupprechter, Günther
Journal ArticleIn: Accounts of Chemical Research, vol. 47, no. 10, pp. 3071–3079, 2014.
Abstract | Links | BibTeX | Tags: P08, P10, pre-TACO
@article{Foettinger2014,
title = {In Situ Spectroscopy of Complex Surface Reactions on Supported Pd–Zn, Pd–Ga, and Pd(Pt)–Cu Nanoparticles},
author = {Karin Föttinger and Günther Rupprechter},
doi = {10.1021/ar500220v},
year = {2014},
date = {2014-09-23},
journal = {Accounts of Chemical Research},
volume = {47},
number = {10},
pages = {3071--3079},
publisher = {American Chemical Society (ACS)},
abstract = {It is well accepted that catalytically active surfaces frequently adapt to the reaction environment (gas composition, temperature) and that relevant “active phases” may only be created and observed during the ongoing reaction. Clearly, this requires the application of in situ spectroscopy to monitor catalysts at work. While changes in structure and composition may already occur for monometallic single crystal surfaces, such changes are typically more severe for oxide supported nanoparticles, in particular when they are composed of two metals. The metals may form ordered intermetallic compounds (e.g. PdZn on ZnO, Pd_{2}Ga on Ga_{2}O_{3}) or disordered substitutional alloys (e.g. PdCu, PtCu on hydrotalcite). We discuss the formation and stability of bimetallic nanoparticles, focusing on the effect of atomic and electronic structure on catalytic selectivity for methanol steam reforming (MSR) and hydrodechlorination of trichloroethylene. Emphasis is placed on the in situ characterization of functioning catalysts, mainly by (polarization modulated) infrared spectroscopy, ambient pressure X-ray photoelectron spectroscopy, X-ray absorption near edge structure, and X-ray diffraction. In the present contribution, we pursue a two-fold, fundamental and applied, approach investigating technologically applied catalysts as well as model catalysts, which provides comprehensive and complementary information of the relevant surface processes at the atomic or molecular level. Comparison to results of theoretical simulations yields further insight.
Several key aspects were identified that control the nanoparticle functionality: (i) alloying (IMC formation) leads to site isolation of specific (e.g. Pd) atoms but also yields very specific electronic structure due to the (e.g. Zn or Ga or Cu) neighboring atoms; (i) for intermetallic PdZn, the thickness of the surface alloy, and its resulting valence band structure and corrugation, turned out to be critical for MSR selectivity; (ii) the limited stability of phases, such as Pd_{2}Ga under MSR conditions, also limits selectivity; (iii) favorably bimetallic catalysts act bifunctional, such as activating methanol AND water or decomposing trichlorothylene AND activating hydrogen; (iv) bifunctionality is achieved either by the two metals or by one metal and the metal–oxide interface; (v) intimate contact between the two interacting sites is required (that cannot be realized by two monometallic nanoparticles being just located close by).
The current studies illustrate how rather simple bimetallic nanoparticles may exhibit intriguing diversity and flexibility, exceeding by far the properties of the individual metals. It is also demonstrated how complex reactions can be elucidated with the help of in situ spectroscopy, in particular when complementary methods with varying surface sensitivity are applied.},
keywords = {P08, P10, pre-TACO},
pubstate = {published},
tppubtype = {article}
}
Several key aspects were identified that control the nanoparticle functionality: (i) alloying (IMC formation) leads to site isolation of specific (e.g. Pd) atoms but also yields very specific electronic structure due to the (e.g. Zn or Ga or Cu) neighboring atoms; (i) for intermetallic PdZn, the thickness of the surface alloy, and its resulting valence band structure and corrugation, turned out to be critical for MSR selectivity; (ii) the limited stability of phases, such as Pd2Ga under MSR conditions, also limits selectivity; (iii) favorably bimetallic catalysts act bifunctional, such as activating methanol AND water or decomposing trichlorothylene AND activating hydrogen; (iv) bifunctionality is achieved either by the two metals or by one metal and the metal–oxide interface; (v) intimate contact between the two interacting sites is required (that cannot be realized by two monometallic nanoparticles being just located close by).
The current studies illustrate how rather simple bimetallic nanoparticles may exhibit intriguing diversity and flexibility, exceeding by far the properties of the individual metals. It is also demonstrated how complex reactions can be elucidated with the help of in situ spectroscopy, in particular when complementary methods with varying surface sensitivity are applied.