Atomic-scale design protocols towards energy, electronic, catalysis and sensing applications

Resume : Layered perovskites AnBnO3n 2 exhibit a natural internal stacking in blocks of n octahedra along (110), and are interesting players in the field of multiferroicity and beyond [1-4]. Our showcase are two n=5 materials which qualify as the first example of ferroelectric metal and, respectively, ferromagnetic multiferroic metal: Bi5Ti5O17, which exhibits coexisting metallicity and spontaneous polarization (P along the stacking direction) as well as a switchable depolarizing field in a finite system [1]; and Bi5Mn5O17, a ferromagnet with coexisting metallicity and spontaneous polarization (P transverse to the stacking direction) thanks to an unusual sheet-like Fermi surface [4]. In both cases the polar distortion involves Bi-O bonding-driven off-centering. Further, the n=4 material La2Ti2O7 (a band insulator and ferroelectric, due to uncompensated rotations) becomes upon magnetic doping either a ferroelectric weak-ferromagnet (La2Mn2O7) with anomalously large linear magnetoelectric coupling [2] or a ferroelectric ferromagnet (V-doped La2Ti2O7 [2,3]) with magnetization inversion upon polarization inversion, i.e. quintessential magnetoelectricity. Refs: [1] A. Filippetti, V. Fiorentini, F. Ricci, P. Delugas, and J. Iniguez: Prediction of a native ferroelectric metal, Nature Comm. 7, 11211 (2016). [2] M. Scarrozza, M. B. Maccioni, G. M. Lopez, and V. Fiorentini, Topological multiferroics, Phase Trans. 88, 953 (2015) [3] M. Scarrozza, A. Filippetti, and V. Fiorentini: Ferromagnetism and orbital order in a topological ferroelectric, Phys. Rev. Lett. 109, 217202 (2012); Multiferroicity in vanadium-doped LaTiO: insights from first principles, Eur. Phys. J. 86, 128 (2013) [4] A. Urru et al., to be published

Resume : For future low power-consumption nanoelectronics, a room-temperature single-electron transistor may be configured by placing a small (few nm diam.) Si nanodot in a thin (<10 nm) SiO2 interlayer in Si. This can be achieved by ion-irradiation induced interface mixing, which turns the oxide layer into metastable SiOx, and subsequent high-temperature thermal decomposition which leaves, for a sufficiently small mixed volume, a single Si nanodot in the SiO2 layer. Corresponding ion mixing simulations have been performed using the binary collision approximation (BCA)[1], followed by kinetic Monte-Carlo (KMC) simulations [2] of the decomposition process, with good qualitative agreement with the structures observed in related experiments. Quantitatively, however, the BCA simulation appears to overestimate the mixing effect. This is attributed to the neglect of the positive entropy of mixing of the Si-SiO2 system, i.e. the immiscibility counteracts the collisional mixing by “up-hill diffusion” [3]. Consequently, intermitting KMC diffusion steps have been introduced into the BCA mixing simulation, resulting in an excellent predictive power for the irradiation step of the production process. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 688072. • [1] W. Möller et al., NIM B, 322, 23–33 • [2] M. Strobel et al., PRB 64, 245422 • [3] B. Liedke et al., NIM B 316 (2013) 56–61

Resume : Ferroelectric domain walls are emerging as robust 2D systems with promising functionality. Recent scanning tunneling and impedance microscopy studies revealed DC and AC conductivity, 2D electron gas and modified chemistry at ferroelectric domain walls. We study phonons localized at ferroelectric domain walls, and scattering of bulk phonons off ferroelectric domain walls using continuum theory and discrete models. We also discuss signatures of these phenomena in scanning impedance microscopy data.

Resume : The electronic and optical properties of monolayer Transition Metal Dichalcogenides such as MoS2, and WS2 are dominated by excitonic effects due to large binding energies from 2D confinement, spin splitting of the valence band, and inversion symmetry breaking. Previous Raman spectroscopy studies have investigated excited excitonic states1, symmetry dependent exciton-phonon coupling 2, thermal conductivity 3, and interlayer coupling4. However these studies are often limited by low excitation energy resolution or are only performed at a single temperature. We present a temperature dependent resonance Raman spectroscopy study on CVD grown monolayer WS2 flakes using excitation energies from 1.86eV to 2.16eV in resonance with the A exciton. Resonance Raman profiles were obtained for a range of temperatures from 4K to 295K, and for multiple phonons including A1’, E’, 2ZA, LA, 2LA, and an unassigned peak attributed to two phonon Raman scattering. The high energy resolution of the resonance Raman profiles allowed observation of both excitons and trions at 4K for the first time, with energies 2.04eV and 2.063eV respectively. Modelling of the Raman scattering amplitude demonstrates that exciton-trion scattering is also required to explain the results. The amplitudes of the scattering terms allow the coupling strength of different phonons to excitons, trions, and exciton-trion scattering to be probed. In addition we discuss how two-phonon scattering peaks allow us to use large wavevector phonons to probe the dark exciton density of states. The resonance profiles for two-phonon, large-wavevector processes are shown to be well described by the same initial and final state resonance model used to describe the single phonon processes. This indicates that dark excitons in WS2 probed in these experiments are a continuum of states.

Resume : I will discuss antiferroelectric (AFE) materials whose anomalous response to applied electric fields makes them attractive, for example, as capacitors for pulse-power applications that require a fast energy release. After summarizing the basic phenomenology and our current understanding of classic compounds like PbZrO3 [1], I will address the question of how to induce AFE behavior by suitable chemical doping of a ferroelectric (FE) material, showing representative first-principles results for BiFeO3-RFeO3 solid solutions [2,3,4], where R is a lanthanide. I will then focus on the representative case of BiFeO3-NdFeO3 mixtures, to show that it is possible to predict optimum conditions (composition and cationic Bi-Nd order, direction of appied electric field) yielding enhanced functional properties of such AFEs [5]. In particular, I will discuss the optimization of the room-temperature polarization vs. electric field hysteresis loop, which determines the performance in energy applications and can be simulated by using first-principles-based effective models that I will briefly introduce [6]. Time allowing, I will outline current prospects on tuning AFE behaviors, or even inducing novel ones, in nano-structured materials. Work done in collaboration with many colleagues, particularly the group of L. Bellaiche at U. Arkansas (USA). Work at LIST funded by Luxembourg National Research Fund. [1] First-principles study of the multimode antiferroelectric transition of PbZrO3, Jorge Íñiguez, Massimiliano Stengel, Sergey Prosandeev and L. Bellaiche, Physical Review B 90, 220103(R) (2014). [2] First-principles investigation of the structural phases and enhanced response properties of the BiFeO3-LaFeO3 multiferroic solid solution, O. E. González-Vázquez, Jacek C. Wojdeł, Oswaldo Diéguez and Jorge Íñiguez, Physical Review B 85, 064119 (2012). [3] Finite-temperature properties of rare-earth-substituted BiFeO3 multiferroic solid solutions, Bin Xu, Dawei Wang, Jorge Íñiguez and L. Bellaiche Advanced Functional Materials 25, 552 (2015). [4] Electric phase diagram of bulk BiFeO3, Massimiliano Stengel and Jorge Íñiguez, Physical Review B 92, 235148 (2015). [5] Designing lead-free antiferroelectrics for energy storage, Bin Xu, Jorge Íñiguez and L. Bellaiche, Nature Communications 8, 15682 (2017). [6] Novel nanoscale twinned phases in perovskite oxides, S. Prosandeev, Dawei Wang, Wei Ren, Jorge Íñiguez and L. Bellaiche, Advanced Functional Materials 23, 234 (2013).

Resume : Many processes in organic devices, such as charge transport, are critically influenced by the packing of the molecules, and thus ultimately influenced by the crystal structure of the semi-crystalline semiconductors. Semi-crystalline materials are likely to exhibit different polymorphs, depending on the structure of the side chains, the molecular weight and the processing conditions. As a consequence, designing new materials for improved efficiency is a truly multi-parameter problem and often yields disappointing results. Being able to predict the likely crystal polymorph of a given molecule as a function of temperature, or in other words, drawing the phase diagram of the material, is therefore an important challenge. In this work, we choose as a model system 3-hexylthiophene (3HT) oligomers of different length. We represent the molecules by a modified version of the force field by Moreno et al.1 We investigate potential crystal structures by selecting a number of space groups that are consistent with the likely trans-geometry of the 3HT oligomers and then building a crystal. We find the unit cell parameters for each space group (stacking, lamellar stacking distances and the unit cell angles), by scanning the parameter space using molecular mechanics simulations. We rank the minimised crystal structures according to the Helmholtz free energy, rather than potential energy, in order to evaluate the results against thermodynamic data. Finally, we compare our results with a thermodynamic study of 3HT oligomers.2,3 This step allows us to validate our method and to ultimately accept or reject the proposed crystal structures. 1. M. Moreno, M. Casalegno, G. Raos, S. V. Meille, R. J. Po J. Phys. Chem. B, 2010, 114, 1591-1602. 2. F. P. V. Koch, P. Smith, M. Heeney J. Am. Chem. Soc. 2013, 135, 13695-13698 3. F. P. V. Koch, M. Heeney, P. Smith J. Am. Chem. Soc. 2013, 135, 13699-13709

Resume : One of the most significant challenges in the development of water splitting device is finding efficient new solar-energy absorber materials. For an efficient conversion of the energy from a source of visible light a given semiconductor must fulfill strict requirements such as: an appropriate band gap, high dielectric constant, good charge carrier mobility and suitable band positions to perform hydrogen and oxygen evolution water splitting half-reactions. Therefore, these properties are of crucial importance in designing new materials for solar energy conversion. Computational chemistry, mainly based on Density Functional Theory (DFT), has proven to be highly reliable to reproduce these properties, generally difficult to obtain experimentally. Consequently, a step forward in designing new materials for the aforementioned application can be done by using DFT to predict in silico properties of never synthetized semiconductors. In this talk, the properties of YTaON2 and YTiO2N, that were never characterized experimentally, will be presented based on DFT calculations. The discussion will include considerations on the thermodynamic stability of the proposed polymorphs constructed by varying anion ordering along with comparisons with the known parent compounds: LaTaON2 and LaTiO2N. DFT results shows that YTaON2 has a direct 2.1 eV band gap, advantageous dielectric, and transport properties as compared to the LaTaON2 analogue, previously proposed as promising visible light absorber semiconductor for solar-fuels.

Resume : Essential materials properties can now be assessed through ab initio methods. When coupled with the exponential rise in computational power, this predictive power provides an opportunity for large-scale computational searches for new materials. We can now screen thousands of materials by their computed properties even before the experiments. This computational paradigm allows experimentalists to focus on the most promising candidates, and enable researchers to efficiently and rapidly explores new chemical spaces. In this talk, I will present the challenges as well as opportunities in materials discovery in high-throughput ab initio computing for opto-electronic materials. I will especially focus on results on p-type transparent conducting materials but also on very recent work on electrides. The impact of high-throughput computing is multiplied when the generated data is shared with free and easy access. I will finish my talk by presenting the Materials Project (http://www.materialproject.org), a collaborative project which precisely targets such a data dissemination.

Resume : Anatase titanium dioxide (TiO2) has been extensively applied as a support and a catalyst in various applications. Contrast to the stability, the reactive (001) facet becomes more attractive for catalytic reactions than the stable (101) surface. Herein, the catalytic and electronic charge nature of the anatase-TiO2 (001) and (101) surfaces were elucidated by using a plane-wave based density functional theory (DFT). Our investigation indicates that the (001) facet reveals promising catalytic properties for a selective catalytic reduction of NO using NH3 (SCR-NH3 of NO) and a H2S desulfurization at low temperatures. Their rate determining steps require activation energies approximately 13 to 15 kcal/mol. The obtained results agree well with the experimental observation that active sites, i.e. five-fold-coordinate Ti atoms (Ti5c) and two-fold-coordinate O atoms (O2c), play important roles on the NH3-SCR of NO reaction over the (001) surface. The insights into mechanisms and charge properties assure the superior catalytic performance of this (001) surface compared to the (101) surface. According to this finding, the anatase-TiO2 (001) catalyst is not only promising for these pollutant removal, but it is also attractive for using in other catalytic applications.

Resume : The first step of Fischer-Tropsch Synthesis (FTS), which converts syngas (CO/H2) to hydrocarbons within the gas-to-liquid technology, consists in the activation of CO in a CO*/H* adlayer on the surface of metallic catalysts (Ru, Co, Fe). Since FTS activity and selectivity depend on CO cleavage, the elucidation of reaction mechanisms and active sites for this transformation has been a very active field of research, with static DFT approaches playing a central role.(1-3) Two main mechanisms for CO cleavage have been proposed for Ru catalysts based on static Density Functional Theory (DFT) calculations: the direct C–O cleavage (on step-edge sites) and the hydrogen-assisted route (on flat surfaces). For the former CO cleavage on different surface sites present on Ru nanoparticles, we recently found there is a particle size effect that can be rationalized via first principles calculations combined with bonding analysis.(1) Nevertheless, in order to compare the two proposed mechanisms, it is needed to go beyond the static simulation approach by introducing adlayer and coverage effects using mobile and reactive co-adsorbates, under finite temperatures since the diffusion of surface species and the interaction of the reaction intermediates with the co-adsorbates can modulate the reaction path. Here, we evaluate how finite temperature effects influence CO cleavage mechanisms during Ru FTS using ab initio molecular dynamics (AIMD) simulations on Ru flat and stepped model surfaces covered with a CO*/H* adlayer.(4) 1. L. Foppa, C. Copéret, A. Comas-Vives, J. Am. Chem. Soc. 2016, 138, 16655. 2. B. T. Loveless, C. Buda, M. Neurock, E. Iglesia, J. Am. Chem. Soc. 2013, 135, 6107. 3. G. T. K. Gunasooriya, A. P. van Bavel, H. P. C. E. Kuipers, M. Saeys, ACS Catal. 2016, 6, 3660. 4. L. Foppa, M. Iannuzzi, C. Copéret, A. Comas-Vives, 2018, submitted.

Resume : Understanding processes at electrochemical electrode-electrolyte interfaces is crucial in order to improve devices in electrochemical energy storage and conversion, such as batteries or fuel cells. In spite of this relevance, our knowledge about microscopic structures and processes at these interfaces is still rather limited. The theoretical description of these interfaces is hampered by at least two factors. i) In electrochemistry, properties of the electrode-electrolyte interfaces are governed by the electrode potential which adds considerable complexity to the theoretical treatment since charged surfaces have to be considered. ii) The theoretical treatment of processes at solid-liquid interfaces necessitates a proper description of the liquid which in principle requires to perform computationally expensive statistical averages. I will in particular focus on how, despite these obstacles, the electrochemical environment can be appropriately and efficiently taken into account in theoretical first-principles studies. For example, the presence of the electrolyte can be treated in a grand-canonical approach as a reservoir. Furthermore, in order to design interfaces with improved properties, the concept of descriptors can be rather helpful. It will be discussed whether the height of metal self-diffusion barriers can serve as a descriptor for the occurrence of dendrite growth in batteries which is one of the major issues in the safe operation of batteries.

Resume : In order to evaluate the potential use of metal-free hexagonal boron nitride (h-BN) nanosheet catalysts, a study was performed, within the frame of density functional theory (DFT), on the formic acid (FA) dehydrogenation to CO2 and H2 that occurs on hydrogen-activated h-BN defects. In the BN material model, the activated site constellations were obtained by removing adjacent B, N couples and partially hydrogenating them. Different mechanistic hypotheses were considered. In particular, the possibility of preferentially dehydrogenating O or C atoms of FA, either by N or B sites of h-BN was evaluated. The calculated energy profiles would suggest that the expected mechanism firstly involves the dehydrogenation of the C atom and then the dehydrogenation of the O one, through a five-terms cyclic transition state. In the latter, the carboxylic oxygen was bound to a B site of h-BN. On the grounds of the theoretical results obtained, it was conceived an experimental study, which included defective h-BN nanosheet catalyst synthesis as well as its morpho-structural characterization and the FA catalytic decomposition analysis. In this case, the conversion of FA to CO2 and H2 clearly increased along with the hydrogenation degree of the boron nitride based catalyst, seeming to experimentally confirm the H2 defect activation, promoting the dehydrogenation processes.

Resume : Chalcogenide phase-change (PC) materials are widely used in data storage due to their ability to switch reversibly between crystalline (electrically conductive, optically reflective) and amorphous (resistive, non-reflective) phases. The switching is achieved with a short electric or laser pulse, and the current state can be read with a less powerful one. The memory is non-volatile, and rewritable in timescale of nanoseconds. A paper published in 2011 [1] reported the same behaviour in crystalline heterostructure with the switching between two crystalline states that behaved not only similarly but with better operating characteristics than the alloy material. Today's simulation methods allow screening of different materials with good accuracy. However, the number of possible layer sequences in a chalcogenide heterostructure is high enough to make 'brute-force' screening not feasible. A genetic algorithm is known to perform well when searching for a global minimum in a complex landscape with a large number of local minima. The results of genetic algorithm search for the most stable heterostructure with Ge2Sb2Te5 overall chemical composition are discussed [2]. Based on the search, a potential structure for the phase-change material is suggested, with a XRD pattern that agrees with experimental pattern of an epitaxially grown structure. [1] Robert E. Simpson et al., Nat. Nanotechnol., 6, 501–505 (2011). [2] J. Kalikka et al., Nanoscale 8, 18212-18220 (2016).

Resume : The number of possible materials is practically infinite, while only few hundred thousands of (inorganic) materials are known to exist and for few of them even basic properties are systematically known. In order to speed up the identification and design of new and novel optimal materials for a desired property or process, strategies for quick and well-guided exploration of the materials space are highly needed. A desirable strategy would be to start from a large body of experimental or theoretical data, and by means of “data-analytics” methods, to identify yet unseen patterns or structures in the data. Specifically I will describe how to spot yet unseen patterns or structures in the data, by identifying the key atomic and collective physical actuators by compressed sensing and machine learning. This enables us to build maps of materials where different regions correspond to materials with different properties. As the connections between actuators and materials properties are intricate, an attempt to describe the relationship in terms of an insightful physical model may be pointless. I will demonstrate our methodology for describing and predicting 2D topological insulators, the metal/insulator classification, catalytic CO2 activation, and more.

Resume : In this talk, we shall discuss the application of single-particle and quasiparticle approaches for the calculation of the properties of complex materials from a first principles perspective. Beside reviewing the fundamental theories we describe the technical procedures to obtain quantitative predictions without adjustable parameters using self-consistent hybrid functionals (scPBE0), GW, the Bethe-Salpeter equation (BSE), and DFT+U with interaction parametrs U/J derived from the constrained random phase approximation. Specific topics include: band gaps and band structure, convergence protocols in GW (comparison between the conventional approach based on an incremental variation of a specific set of parameters and the basis-set extrapolation scheme), and optical properties using the BSE and model-BSE methods. Most of the examples will focus on (spin-orbit) transition metal oxides, where the entanglement of orbital, spin and lattice interactions gives rise to collective effects which are difficult to model and understand, but are of key importance for practical functionalizations.

Resume : We investigated the atomic scale tribological properties of transition metal dichalcogenides (TMDs), using ab-initio techniques. Such compounds are formed by triatomic layers with MX2 stoichiometry (M: transition metal cation, X: chalcogen anion) held together by van der Waals forces. We considered 6 prototypical MX2 TMDs (M=Mo, W; X=S, Se, Te) with hexagonal P63/mmc symmetry, focusing on how specific phonon modes contribute to their intrinsic friction. Within the DFT framework, we described the exchange-correlation interaction energy by means of the PBE functional, including long range dispersion interactions in the Grimme formulation (DFT-D3 van der Waals). We identified and disentangled the electro-structural features that determine the intra- and inter-layer motions affecting the intrinsic friction by means of electro-structural descriptors such as orbital polarization, bond covalency and cophonicity.1 We show how the phonon modes affecting the intrinsic friction can be adjusted by means of an external electrostatic field. In this way, the electric field turns out to be a knob to control the intrinsic friction. The presented outcomes are a step forward in the development of layer exfoliation and manipulation methods, which are fundamental for the production of TMD-based optoelectronical devices and nanoelectromechanical systems. [1] Cammarata, Antonio and Polcar, Tomas (2015) DOI 10.1039/C5RA24837J

Resume : It is estimated that 23% of all energy consumed is lost on energy dissipation due to friction and wear. The control of energy loss under tribological conditions is then mandatory for a sustainable development. To this aim, tribological research has focused on transition metal dichalcogenides (TMD) which are considered to be among the best solid lubricants due to their lamellar structure. Specifically, molybdenum disulfide has revealed its super low friction behavior [1]. However, a full understanding of the mechanism behind this behavior remains lacking. In this contribution we aim to elucidate the phenomena taking place at the nanoscale when two layers of molybdenum disulfide slide one atop of another. In particular, by means of molecular dynamics simulations, we studied the effect of rotational sliding anisotropy [2] (i.e., the changing frictional behavior upon a non-zero misfit angle between the two layers or varying the sliding direction) on the energy dissipation due to friction. We simulated different sliding conditions (varying e.g. normal load) in order to highlight their effect on the lubricating properties. These results will help on the one hand to identify the fundamental mechanisms that govern friction at an atomistic level in TMD’s, as well as providing guidelines for the design of novel layered materials with improved tribological properties.

Resume : The surfaces of many late transition metals are oxidized under ambient conditions or at increased oxygen pressures, which has strong implications for corrosion and catalysis. Stable O-enriched states resulting from oxidation may consist of the metal surface with high concentration of adsorbed O atoms, the corresponding metal-oxide, or something in between (e.g. surface oxides). The quantitative atomistic modeling of oxidation reactions catalyzed on transition metals often therefore requires accounting for the reactivity on more than one stable phase. In this work, CO oxidation on Pd(100) and the corresponding surface oxide phase PdO(101)/Pd(100) formed on it is addressed by means of Density Functional Theory calculations and kinetic Monte Carlo simulations. We use a novel multi-lattice microkinetic modeling approach to investigate the role of the metal and oxide phases and how their coexistence under different operation conditions affects catalytic performance. This also allows probing the relevance of sites at the interface between the two phases and the effect of phase transitions on the overall reactivity. We furthermore show how results from this two-phase model can be generalized to understand the kinetics of multifunctional catalysts combining a metal, an oxide, and their interface.

Resume : A common goal for materials employed in nuclear environments is to exhibit the highest radiation tolerance. The lifetimes of current and even more of new-build and future reactors are largely determined by materials issues such as embrittlement and swelling in fuel cladding and structural components. Radiation tolerance-related requirements are further boosted by the higher performance expected for Generation IV fission reactors and fusion reactors, which will expose materials to much higher numbers of atomic displacements then current and near-feature reactors. In the process of energy production via fission (and, to some extent, by fusion), both fuel components and structural materials are subject to substantial radiation damage, which initially appears in the form of local intrinsic point defects within the material (i.e. vacancies and interstitials). The point defects agglomerate, interact with the underlying microstructure and lead to undesirable effects such as blistering and radiation-induced embrittlement, which render the materials unsuitable for the desired application. Another important factor is represented by helium embrittlement. He originates from the transmutation of reactor elements which can release alpha particles that acquire electrons to become helium atoms. He is insoluble and mobile in most metals and migrates to grain boundaries and interfaces where it forms bubbles leading to embrittlement. Many of the materials being developed for deployment in these environments are based on incremental improvements to existing materials such as Oxide Dispersion Strengthened (ODS) steels. Here, we present nanoscale Zr-Nb metallic multilayer composite as s a model material to understand the role of interfaces, defects and He in radiation environments using density functional theory in an attempt to create radiation damage tolerant, self-healing material.

Resume : High compressive strains have been used as a way to tune physical properties of three-dimensional perovskite crystals. Pressure in the GPa range generates structural distorsions in perovskite lattice, affecting the electronic structure and modifying optical and transport properties. Surprisingly, stacks of hyrid organic-inorganic perovskite flakes demonstrate tunability of optical spectra at much lower pressures, in the range of tens of MPa. Pristine flakes are near-white emitting, and in-situ photoluminescence experiments during loading and unloading in a mechanical pressure cell reveal drastic change in their optical emission spectrum, particularly an enhancement of the blue emission. Using first principles simulations, we are able to reproduce the main features of the optical properties and to analyze their variations under compressive strain.

Resume : Hybrid organic-inorganic compounds attract a lot of interest for their flexible structures and multifunctional properties. For example, they can have coexisting magnetism and ferroelectricity whose possible coupling gives rise to magnetoelectricity. Here using first-principles computations, we show that, in a perovskite metal-organic framework (MOF), the magnetic and electric orders are further coupled to optical excitations, leading to an Electric tuning of the Magneto-Optical Kerr effect (EMOKE). Moreover, the Kerr angle can be switched by reversal of both ferroelectric and magnetic polarization only. The interplay between the Kerr angle and the organic-inorganic components of MOFs offers surprising unprecedented tools for engineering MOKE in complex compounds. Note that this work may be relevant to acentric magnetic systems in general, e.g., multiferroics.