THEORY DEPARTMENT
Fritz Haber Institute of the Max Planck Society

All FHI Seminars

Is the CO2 molecule really linear?
Speaker: Dr. Philip R. Bunker
 Steacie Laboratory, National Research Council of Canada, Ottawa, Ontario, Canada
Time:Friday, 20th September 2019, 9:30 AM
Location: Haber-Villa
Organized: MP
Abstract: This talk has arisen from my efforts to defend the position taken by Per Jensen that CO2 is bent. If one determines the OCO bending angle using quantum mechanics, or if one were to use a Coulomb Explosion Imaging experiment, it appears to me that he is correct. The talk ought to be accessible to anybody that has some small knowledge of quantum mechanics, but you might not agree with the conclusion.

Ultrafast Phonon and Carrier Dynamics at Semiconductor Hetero-interfaces Studied by Transient Reflection and Transmission Measurements
Speaker:Kunie Ishioka
 NIMS Japan
Time:Monday, 23rd September 2019, 2:00 PM
Location: PC Seminar Room G2.06, Building G
Organized: PC
Abstract: Hetero-interfaces between two different materials often show different electronic and phononic properties from bulk, which gives a basis to modern opto-electronic device technologies. In the present talk I present our recent results on two different hetero-interface systems. Thin GaP films can be grown on Si(001) with nearly perfect lattice match. We perform pump-probe reflectivity measurements on the buried GaP/Si(001) interface either above or below-bandgap excitation. The above-gap photoexcitation can induce coherent LO phonons in the GaP film, whose coupling with photoexcited plasma is found to depend on the GaP thickness due to the quasi-two-dimensional confinement of the plasma [1]. The same laser pulse can also generate coherent LA phonons at the GaP/Si interface as well as at the GaP surface [2], suggesting a possibility for an application as an opto-acoustic transducer. Lead halide perovskite solar cells, which have been developing rapidly in the past few years, typically consist of a perovskite film sandwiched between thin layers of electron- and hole-transport layers. We monitor the charge separation dynamics at the interfaces of CH3NH3PbI3 with three typical hole transport materials (HTMs) using differential transient transmission measurements [3]. The differential signals reveals the hole injection from the perovskite to organic HTMs, PTAA and PEDOT:PSS, to occur on the time scale of 1 ps, whereas that to inorganic NiOx an order of magnitude longer. We find an anti-correlation between the hole injection time and the fill factor, one of the key device properties, of the solar cells made with the three different HTM References: [1] Ishioka et al., J. Phys.: Cond. Matter 31, 094003 (2019). [2] Ishioka et al., Appl. Phys. Lett. 111, 062105 (2017). [3] Ishioka et al., J. Phys. Chem. Lett. 8, 3902 (2017).

Introduction to Statistical Mechanics Applied to Catalysis
Speaker:Prof. S. Ted Oyama
 University of Tokyo Department of Chemical Systems Engineering
Time:Monday, 23rd September 2019, 3:30 PM
Location: F Building, Room 0.04
Organized: AC
Abstract: Content of the lectures will be: 1)Boltzmann distribution 2)Partition functions 3)Thermodynamic functions 4)Entropy 5)Translational entropy 6)Vibrational entropy 7)Rotational entropy 8)Transition state theory 9)Pre-exponential factors

Introduction to Statistical Mechanics Applied to Catalysis
Speaker:Prof. S. Ted Oyama
 University of Tokyo Department of Chemical Systems Engineering
Time:Tuesday, 24th September 2019, 3:30 PM
Location: F Building, Room 0.04
Organized: AC
Abstract: Content of the lectures will be: 1)Boltzmann distribution 2)Partition functions 3)Thermodynamic functions 4)Entropy 5)Translational entropy 6)Vibrational entropy 7)Rotational entropy 8)Transition state theory 9)Pre-exponential factors

Introduction to Statistical Mechanics Applied to Catalysis
Speaker:Prof. S. Ted Oyama
 University of Tokyo Department of Chemical Systems Engineering
Time:Wednesday, 25th September 2019, 3:30 PM
Location: F Building, Room 0.04
Organized: AC
Abstract: Content of the lectures will be: 1)Boltzmann distribution 2)Partition functions 3)Thermodynamic functions 4)Entropy 5)Translational entropy 6)Vibrational entropy 7)Rotational entropy 8)Transition state theory 9)Pre-exponential factors

Introduction to Statistical Mechanics Applied to Catalysis
Speaker:Prof. S. Ted Oyama
 University of Tokyo Department of Chemical Systems Engineering
Time:Thursday, 26th September 2019, 3:30 PM
Location: F Building, Room 0.04
Organized: AC
Abstract: Content of the lectures will be: 1)Boltzmann distribution 2)Partition functions 3)Thermodynamic functions 4)Entropy 5)Translational entropy 6)Vibrational entropy 7)Rotational entropy 8)Transition state theory 9)Pre-exponential factors

Observation of Surface Species and Reactions Pathways on Solid Acids
Speaker:Prof. Friederike C. Jentoft
 Department of Chemical Engineering, University of Massachusetts
Time:Monday, 30th September 2019, 11:00 AM
Location: Building F, Room 0.04
Organized: AC
Abstract: Numerous transformations en route from biomass- or petroleum-derived feedstocks to chemicals and fuels are achieved by means of acid catalysts; for example, isomerization, dehydration, cracking, and alkylation all proceed on acid sites. While mechanisms for these transformations have been proposed in the literature, direct evidence for postulated intermediates and their involvement is often lacking. Our fundamental research into surface species and reaction pathways is motivated by practical challenges, that is, controlling selectivity and avoiding coke formation. In recent years, we have advanced the interpretation of IR and UV-vis spectra of stable surface species on solid acids through a variety of measures, including use of model reactants and well-defined catalysts such as zeolites, specific experiments to discriminate neutral and charged surface species, analogies with liquid phase chemistry, and insight from theory. The lecture introduces these methodologies and the resulting correlations. The acquired knowledge of spectra and surface reaction chemistry is then applied to identify the complex mixture of surface species formed during methanol-to-olefins conversion. Several mechanisms are currently discussed in the literature for this reaction that suggest a role of stable surface species as active intermediates (“hydrocarbon pool)”. A comparison of the proposed intermediates and catalytic cycles with our spectroscopic findings questions the validity of some of these mechanisms while lending more credence to others.

The one-step model of 2PPE combined with inverse photoemission: applications to simple metals and complex compounds
Speaker:Jürgen Braun
 Ludwig-Maximilians Universität
Time:Tuesday, 1st October 2019, 2:00 PM
Location: PC Seminar Room G2.06, Building G
Organized: PC
Abstract: A brief introduction to the theory of angle-resolved photoemission spectroscopy (ARPES) of solids is given with an emphasis on the so-called one-step model of photoemission that describes excitation, transport to the surface and the escape to the vacuum in a coherent way. As the latest development a theoretical frame for the description of pump-probe photoemission is presented. The approach is based on a general formulation using the Keldysh formalism for the lesser Green function to describe the real-time evolution of the electronic degrees of freedom in the initial state after a strong pump pulse that drives the system out of equilibrium [1,2,3]. The theory is implemented within the fully relativistic spin-density matrix formulation [4], and is part of the Munich SPR-KKR program package [5]. As a first application, the theoretical description of two-photon photoemission (2PPE) for Ag(100) within the SPR-KKR-approach is introduced [2]. Furthermore, first examples of angular-resolved 2PPE calculations on Fe(100) will be presented where correlation effects are accounted for by means of a static self-energy ΣDMFT(E) obtained for Fe from dynamical mean-field theory. At last the impact of relativistic effects on image potential states on the ferromagntic metals Fe, Co and Ni will be discussed within a combined IPE and 2PPE analysis.. [1] J. Braun, R. Rausch, M. Potthoff, J. Minar, and H. Ebert, Pump-probe theory of angle-resolved photoemission, Phys. Rev. B 91, 035119 (2015). [2] J. Braun, R. Rausch, M. Potthoff , and H. Ebert, One-step theory of two-photon photoemission, Phys. Rev. B 94, 125128 (2016). [3] J. Braun and H. Ebert, Relativistic theory of 2PPE from ferromagnetic materials, Phys. Rev. B 98, 245142 (2018). [4] J. Braun, K. Miyamoto, T. Okuda, M. Donath, A. Kimura, H. Ebert, and J. Minar, Topological behavior of d-like surface resonances: the one-step model in its density matrix formulation applied to W(110), New Journal of Physics 16, 015005 (2014). [5] H. Ebert et al., The Munich SPR-KKR package, version 8.4, http://olymp.cup.uni-muenchen.de/ak/ebert/ SPRKKR (2019).

Nano-optics with 2D materials
Speaker:Pablo Alonso González
 University of Oviedo, Spain
Time:Monday, 14th October 2019, 11:00 AM
Location: PC Seminar Room G2.06, Building G
Organized: PC
Abstract: The advent of two-dimensional (2D) materials with extraordinary optical properties has allowed the visualization of nanolight in the form of low-loss and electrically tunable (active) plasmon polaritons in graphene, or high optical quality phonon polaritons in h-BN or MoO3, introducing a very encouraging arena for scientifically ground-breaking discoveries in nano-optics. In this talk I will show first proof-of-concept devices based on 2D materials for nano-optics.

The slowly-evolving picture of the Pt{110} electrode surface: Is there still something new to learn from single crystal platinum voltammetry?
Speaker:Gary A. Attard
 University of Liverpool, UK
Time:Tuesday, 29th October 2019, 11:00 AM
Location: PC Seminar Room G2.06, Building G
Organized: PC
Abstract: In this lecture, it will be asserted that our understanding of the surface structure of “well-defined” Pt{110} is still far from complete. It is shown that depending on the cooling environment following flame-annealing, several different structural phases may be identified corresponding to (1x1) and variously disordered (1x1) and (1x2) reconstructed surface phases. Furthermore, by utilising stepped Pt{110} electrodes together with CO charge-displacement measurements it is suggested that one may associate “local” values of the potential of zero charge to each of the voltammetric peaks. The consequences of this assertion for the interpretation of the multiplicity of voltammetric curves displayed by all Pt{hkl} electrodes will be discussed. From this fundamental perspective, it will then be demonstrated how nitrate reduction may be used as a quantitative probe of Pt{110}-(1x1) facets present at a Pt nanoparticle. Thus, combined with measurements of other surface site specific redox states to measure the abundance of Pt{111} and Pt{100} sites, a very complete picture of terrace site distributions at Pt nanoparticles may be determined via purely electrochemical approaches.

Personalities and Rivalries that Made Modern Chemistry: Haber, Bosch, Ostwald, Le Chatelier, Nernst, Langmuir, and the Fixation of Nitrogen
Speaker: Dr. Patrick Coffey?
 Visiting Scholar, Office for the History of Science and Technology, University of California, Berkeley
Time:Tuesday, 29th October 2019, 11:15 AM
Location: Seminar Room, Buikding P, Faradayweg 16, 14195 Berlin
Organized: GFW
Abstract: In 1898, William Crookes predicted worldwide famine among the "civilized" countries when South American nitrates, imported as fertilizer, would be exhausted; there was hope, however, and it lay with the chemists. Almost 80% of the air is nitrogen, and if that could be “fixed”, rupturing the strong molecular nitrogen triple bond and forming bonds with oxygen or hydrogen, disaster could be averted. The leading chemists (and chemical companies) were all listening. Fritz Haber, motivated by scientific curiosity, personal ambition, patriotism, greed, and a desire to avenge the slights that Nernst had inflicted upon him, would cross the finish line first. Carl Bosch would take Haber’s laboratory process, which produced a few milliliters of ammonia, and build factories that produced a hundred tons a day. The Haber-Bosch process has changed the world for good and evil; the process uses 1-2% of the world’s total energy production and is responsible for 300 million metric tons of carbon dioxide emissions. In 1896, Arrhenius predicted global warming; fourteen years later, Haber guaranteed it.

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