Johannes Voss

All Publications

• Interpretable Machine Learning Models for Practical Antimonate Electrocatalyst Performance. Chemphyschem : a European journal of chemical physics and physical chemistry Deo, S., Kreider, M., Kamat, G., Hubert, M., Zamora Zeledón, J., Wei, L., Matthews, J., Keyes, N., Singh, I., Jaramillo, T., Abild-Pedersen, F., Burke Stevens, M., Winther, K., Voss, J. 2024: e202400010

  Abstract

  Computationally predicting the performance of catalysts under reaction conditions is a challenging task due to the complexity of catalytic surfaces and their evolution in situ, different reaction paths, and the presence of solid-liquid interfaces in the case of electrochemistry. We demonstrate here how relatively simple machine learning models can be found that enable prediction of experimentally observed onset potentials. Inputs to our model are comprised of data from the oxygen reduction reaction on non-precious transition-metal antimony oxide nanoparticulate catalysts with a combination of experimental conditions and computationally affordable bulk atomic and electronic structural descriptors from density functional theory simulations. From human-interpretable genetic programming models, we identify key experimental descriptors and key supplemental bulk electronic and atomic structural descriptors that govern trends in onset potentials for these oxides and deduce how these descriptors should be tuned to increase onset potentials. We finally validate these machine learning predictions by experimentally confirming that scandium as a dopant in nickel antimony oxide leads to a desired onset potential increase. Macroscopic experimental factors are found to be crucially important descriptors to be considered for models of catalytic performance, highlighting the important role machine learning can play here even in the presence of small datasets.

  View details for DOI 10.1002/cphc.202400010

  View details for PubMedID 38547332

• Factors Affecting the Electron Conductivity in Single Crystal Li₇La₃Zr₂O₁₂ and Li₇P₃S₁₁ ACS APPLIED ENERGY MATERIALS Demir, S., Tekin, A., Chan, Y., Scheurer, C., Reuter, K., Luntz, A. C., Voss, J. 2024; 7 (6): 2392-2404

  View details for DOI 10.1021/acsaem.3c03092

  View details for Web of Science ID 001186312500001

• Number of sites-based solver for determining coverages from steady-state mean-field micro-kinetic models. Journal of computational chemistry Vijay, S., H Heenen, H., Singh, A. R., Chan, K., Voss, J. 2023

  Abstract

  Kinetic models parameterized by ab-initio calculations have led to significant improvements in understanding chemical reactions in heterogeneous catalysis. These studies have been facilitated by implementations which determine steady-state coverages and rates of mean-field micro-kinetic models. As implemented in the open-source kinetic modeling program, CatMAP, the conventional solution strategy is to use a root-finding algorithm to determine the coverage of all intermediates through the steady-state expressions, constraining all coverages to be non-negative and to properly sum to unity. Though intuitive, this root-finding strategy causes issues with convergence to solution due to these imposed constraints. In this work, we avoid explicitly imposing these constraints, solving the mean-field steady-state micro-kinetic model in the space of number of sites instead of solving it in the space of coverages. We transform the constrained root-finding problem to an unconstrained least-squares minimization problem, leading to significantly improved convergence in solving micro-kinetic models and thus enabling the efficient study of more complex catalytic reactions.

  View details for DOI 10.1002/jcc.27263

  View details for PubMedID 38009447

• X-ray free electron laser studies of electron and phonon dynamics of graphene adsorbed on copper PHYSICAL REVIEW MATERIALS Ogasawara, H., Wang, H., Gladh, J., Gallo, A., Page, R., Voss, J., Luntz, A., Diesen, E., Abild-Pedersen, F., Nilsson, A., Soldemo, M., Zajac, M., Attar, A., Chen, M. E., Cho, S., Katoch, A., Kim, K., Kim, K., Kim, M., Kwon, S., Park, S., Ribeiro, H., Sainio, S., Wang, H., Yang, C., Heinz, T. 2023; 7 (2)

  View details for DOI 10.1103/PhysRevMaterials.7.024005

  View details for Web of Science ID 000943101300002

• Atom-Specific Probing of Electron Dynamics in an Atomic Adsorbate by Time-Resolved X-Ray Spectroscopy. Physical review letters Schreck, S., Diesen, E., Dell'Angela, M., Liu, C., Weston, M., Capotondi, F., Ogasawara, H., LaRue, J., Costantini, R., Beye, M., Miedema, P. S., Halldin Stenlid, J., Gladh, J., Liu, B., Wang, H. Y., Perakis, F., Cavalca, F., Koroidov, S., Amann, P., Pedersoli, E., Naumenko, D., Nikolov, I., Raimondi, L., Abild-Pedersen, F., Heinz, T. F., Voss, J., Luntz, A. C., Nilsson, A. 2022; 129 (27): 276001

  Abstract

  The electronic excitation occurring on adsorbates at ultrafast timescales from optical lasers that initiate surface chemical reactions is still an open question. Here, we report the ultrafast temporal evolution of x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) of a simple well-known adsorbate prototype system, namely carbon (C) atoms adsorbed on a nickel [Ni(100)] surface, following intense laser optical pumping at 400 nm. We observe ultrafast (∼100  fs) changes in both XAS and XES showing clear signatures of the formation of a hot electron-hole pair distribution on the adsorbate. This is followed by slower changes on a few picoseconds timescale, shown to be consistent with thermalization of the complete C/Ni system. Density functional theory spectrum simulations support this interpretation.

  View details for DOI 10.1103/PhysRevLett.129.276001

  View details for PubMedID 36638285

• Symmetry-resolved CO desorption and oxidation dynamics on O/Ru(0001) probed at the C K-edge by ultrafast x-ray spectroscopy JOURNAL OF CHEMICAL PHYSICS LaRue, J., Liu, B., Rodrigues, G. S., Liu, C., Torres, J., Schreck, S., Diesen, E., Weston, M., Ogasawara, H., Perakis, F., Dell'Angela, M., Capotondi, F., Ball, D., Carnahan, C., Zeri, G., Giannessi, L., Pedersoli, E., Naumenko, D., Amann, P., Nikolov, I., Raimondi, L., Spezzani, C., Beye, M., Voss, J., Wang, H., Cavalca, F., Gladh, J., Koroidov, S., Abild-Pedersen, F., Kolb, M., Miedema, P. S., Costantini, R., Heinz, T. F., Luntz, A. C., Pettersson, L. M., Nilsson, A. 2022; 157 (16): 164705

  Abstract

  We report on carbon monoxide desorption and oxidation induced by 400 nm femtosecond laser excitation on the O/Ru(0001) surface probed by time-resolved x-ray absorption spectroscopy (TR-XAS) at the carbon K-edge. The experiments were performed under constant background pressures of CO (6 × 10-8 Torr) and O2 (3 × 10-8 Torr). Under these conditions, we detect two transient CO species with narrow 2π* peaks, suggesting little 2π* interaction with the surface. Based on polarization measurements, we find that these two species have opposing orientations: (1) CO favoring a more perpendicular orientation and (2) CO favoring a more parallel orientation with respect to the surface. We also directly detect gas-phase CO2 using a mass spectrometer and observe weak signatures of bent adsorbed CO2 at slightly higher x-ray energies than the 2π* region. These results are compared to previously reported TR-XAS results at the O K-edge, where the CO background pressure was three times lower (2 × 10-8 Torr) while maintaining the same O2 pressure. At the lower CO pressure, in the CO 2π* region, we observed adsorbed CO and a distribution of OC-O bond lengths close to the CO oxidation transition state, with little indication of gas-like CO. The shift toward "gas-like" CO species may be explained by the higher CO exposure, which blocks O adsorption, decreasing O coverage and increasing CO coverage. These effects decrease the CO desorption barrier through dipole-dipole interaction while simultaneously increasing the CO oxidation barrier.

  View details for DOI 10.1063/5.0114399

  View details for Web of Science ID 000876502600007

  View details for PubMedID 36319417

• Data-driven and constrained optimization of semi-local exchange and nonlocal correlation functionals for materials and surface chemistry JOURNAL OF COMPUTATIONAL CHEMISTRY Trepte, K., Voss, J. 2022

  Abstract

  Reliable predictions of surface chemical reaction energetics require an accurate description of both chemisorption and physisorption. Here, we present an empirical approach to simultaneously optimize semi-local exchange and nonlocal correlation of a density functional approximation to improve these energetics. A combination of reference data for solid bulk, surface, and gas-phase chemistry and physical exchange-correlation model constraints leads to the VCML-rVV10 exchange-correlation functional. Owing to the variety of training data, the applicability of VCML-rVV10 extends beyond surface chemistry simulations. It provides optimized gas phase reaction energetics and an accurate description of bulk lattice constants and elastic properties.

  View details for DOI 10.1002/jcc.26872

  View details for Web of Science ID 000787684800001

  View details for PubMedID 35474584

• Hubbard-corrected oxide formation enthalpies without adjustable parameters JOURNAL OF PHYSICS COMMUNICATIONS Voss, J. 2022; 6 (3)

  View details for DOI 10.1088/2399-6528/ac6069

  View details for Web of Science ID 000776457500001

• Simulations of x-ray absorption spectra for CO desorbing from Ru(0001) with transition-potential and time-dependent density functional theory approaches STRUCTURAL DYNAMICS-US Rodrigues, G. S., Diesen, E., Voss, J., Norman, P., Pettersson, L. M. 2022; 9 (1): 014101

  Abstract

  The desorption of a carbon monoxide molecule from a Ru(0001) surface was studied by means of X-ray Absorption Spectra (XAS) computed with Transition Potential (TP-DFT) and Time Dependent (TD-DFT) DFT methods. By unraveling the evolution of the CO electronic structure upon desorption, we observed that at 2.3 Å from the surface, the CO molecule has already predominantly gas-phase character. While C 1s XAS is quite insensitive to changes in the C-O bond length, the O 1s excitation is very sensitive with the π* coming down in energy upon CO bond stretching, which competes with the increase in orbital energy due to the repulsive interaction with the metallic surface. We show in a systematic way that the TP-DFT method can describe the XAS rather well at the endpoints (chemisorbed and gas phase) but is affected by artificial charge transfer and/or incorrect spin treatment in the transition region in cases like CO, where there are low-lying π* orbitals and large exchange interactions between the core 1s and valence-acceptor π* orbitals. As an alternative, we demonstrate by comparing with experimental data that a linear response approach using TD-DFT employing common exchange-correlation functionals and finite-size clusters can yield a good description of the spectral evolution of the 1s → π* transition with correct spin and gas-to-chemisorbed chemical shifts in good agreement with experiment.

  View details for DOI 10.1063/4.0000135

  View details for Web of Science ID 000746515600003

  View details for PubMedID 35071691

  View details for PubMedCentralID PMC8759799

• MCML: Combining physical constraints with experimental data for a multi-purpose meta-generalized gradient approximation. Journal of computational chemistry Brown, K., Maimaiti, Y., Trepte, K., Bligaard, T., Voss, J. 2021

  Abstract

  The predictive power of density functional theory for materials properties can be improved without increasing the overall computational complexity by extending the generalized gradient approximation (GGA) for electronic exchange and correlation to density functionals depending on the electronic kinetic energy density in addition to the charge density and its gradient, resulting in a meta-GGA. Here, we propose an empirical meta-GGA model that is based both on physical constraints and on experimental and quantum chemistry reference data. The resulting optimized meta-GGA MCML yields improved surface and gas phase reaction energetics without sacrificing the accuracy of bulk property predictions of existing meta-GGA approaches.

  View details for DOI 10.1002/jcc.26732

  View details for PubMedID 34406661

• Ultrafast Adsorbate Excitation Probed with Subpicosecond-Resolution X-Ray Absorption Spectroscopy. Physical review letters Diesen, E., Wang, H. Y., Schreck, S., Weston, M., Ogasawara, H., LaRue, J., Perakis, F., Dell'Angela, M., Capotondi, F., Giannessi, L., Pedersoli, E., Naumenko, D., Nikolov, I., Raimondi, L., Spezzani, C., Beye, M., Cavalca, F., Liu, B., Gladh, J., Koroidov, S., Miedema, P. S., Costantini, R., Heinz, T. F., Abild-Pedersen, F., Voss, J., Luntz, A. C., Nilsson, A. 2021; 127 (1): 016802

  Abstract

  We use a pump-probe scheme to measure the time evolution of the C K-edge x-ray absorption spectrum from CO/Ru(0001) after excitation by an ultrashort high-intensity optical laser pulse. Because of the short duration of the x-ray probe pulse and precise control of the pulse delay, the excitation-induced dynamics during the first picosecond after the pump can be resolved with unprecedented time resolution. By comparing with density functional theory spectrum calculations, we find high excitation of the internal stretch and frustrated rotation modes occurring within 200 fs of laser excitation, as well as thermalization of the system in the picosecond regime. The ∼100  fs initial excitation of these CO vibrational modes is not readily rationalized by traditional theories of nonadiabatic coupling of adsorbates to metal surfaces, e.g., electronic frictions based on first order electron-phonon coupling or transient population of adsorbate resonances. We suggest that coupling of the adsorbate to nonthermalized electron-hole pairs is responsible for the ultrafast initial excitation of the modes.

  View details for DOI 10.1103/PhysRevLett.127.016802

  View details for PubMedID 34270277

• Assessing density functionals for describing methane dissociative chemisorption on Pt(110)-(2×1) surface Chinese Journal of Chemical Physics Wei, F., Smeets, E., Voss, J., Kroes, G., Lin, S., Guo, H. 2021; 34: 883

  View details for DOI 10.1063/1674-0068/cjcp2110207

• Accuracy of XAS theory for unraveling structural changes of adsorbates: CO on Ni(100) AIP ADVANCES Diesen, E., Rodrigues, G. S., Luntz, A. C., Abild-Pedersen, F., Pettersson, L. M., Voss, J. 2020; 10 (11)

  View details for DOI 10.1063/5.0028002

  View details for Web of Science ID 000593976400001

• Closing the Gap Between Experiment and Theory: Reactive Scattering of HCl from Au(111) JOURNAL OF PHYSICAL CHEMISTRY C Gerrits, N., Geweke, J., Smeets, E. F., Voss, J., Wodtke, A. M., Kroes, G. 2020; 124 (29): 15944–60

  View details for DOI 10.1021/acs.jpcc.0c03756

  View details for Web of Science ID 000555507000030

• Mechanisms of Two-Electron and Four-Electron Electrochemical Oxygen Reduction Reactions at Nitrogen-Doped Reduced Graphene Oxide ACS CATALYSIS Kim, H., Bukas, V. J., Park, H., Park, S., Diederichsen, K. M., Lim, J., Cho, Y., Kim, J., Kim, W., Han, T., Voss, J., Luntz, A. C., McCloskey, B. D. 2020; 10 (1): 852–63

  View details for DOI 10.1021/acscatal.9b04106

  View details for Web of Science ID 000506725100093

• Adsorption on transition metal surfaces: Transferability and accuracy of DFT using the ADS41 dataset PHYSICAL REVIEW B Sharada, S., Karlsson, R. B., Maimaiti, Y., Voss, J., Bligaard, T. 2019; 100 (3)

  View details for DOI 10.1103/PhysRevB.100.035439

  View details for Web of Science ID 000477888900003

• High-Throughput Screening of Solid-State Li-Ion Conductors Using Lattice-Dynamics Descriptors ISCIENCE Muy, S., Voss, J., Schlem, R., Koerver, R., Sedlmaier, S. J., Maglia, F., Lamp, P., Zeier, W. G., Shao-Horn, Y. 2019; 16: 270-+

  Abstract

  Low lithium-ion migration barriers have recently been associated with low average vibrational frequencies or phonon band centers, further helping identify descriptors for superionic conduction. To further explore this correlation, here we present the computational screening of ∼14,000 Li-containing compounds in the Materials Project database using a descriptor based on lattice dynamics reported recently to identify new promising Li-ion conductors. An efficient computational approach was optimized to compute the average vibrational frequency or phonon band center of ∼1,200 compounds obtained after pre-screening based on structural stability, band gap, and their composition. Combining a low computed Li phonon band center with large computed electrochemical stability window and structural stability, 18 compounds were predicted to be promising Li-ion conductors, one of which, Li3ErCl6, has been synthesized and exhibits a reasonably high room-temperature conductivity of 0.05-0.3 mS/cm, which shows the promise of Li-ion conductor discovery based on lattice dynamics.

  View details for DOI 10.1016/j.isci.2019.05.036

  View details for Web of Science ID 000473321700022

  View details for PubMedID 31203184

  View details for PubMedCentralID PMC6581664

• Specific Reaction Parameter Density Functional Based on the Meta-Generalized Gradient Approximation: Application to H-2 + Cu(111) and H-2 + Ag(111) JOURNAL OF PHYSICAL CHEMISTRY A Smeets, E. F., Voss, J., Kroes, G. 2019; 123 (25): 5395–5406

  Abstract

  Specific reaction parameter density functionals (SRP-DFs), which can describe dissociative chemisorption reactions on metals to within chemical accuracy, have so far been based on exchange functionals within the generalized gradient approximation (GGA) and on GGA correlation functionals or van der Waals correlation functionals. These functionals are capable of describing the molecule-metal surface interaction accurately, but they suffer from the general GGA problem that this can be done only at the cost of a rather poor description of the metal. Here, we show that it is possible also to construct SRP-DFs for H2 dissociation on Cu(111) based on meta-GGA functionals, introducing three new functionals based on the "made-simple" (MS) concept. The exchange parts of the three functionals (MS-PBEl, MS-B86bl, and MS-RPBEl) are based on the expressions for the PBE, B86b, and RPBE exchange functionals. Quasi-classical trajectory (QCT) calculations performed with potential energy surfaces (PESs) obtained with the three MS functionals reproduce molecular beam experiments on H2, D2 + Cu(111) with chemical accuracy. Therefore, these three non-empirical functionals themselves are also capable of describing H2 dissociation on Cu(111) with chemical accuracy. Similarly, QCT calculations performed on the MS-PBEl and MS-B86bl PESs reproduced molecular beam and associative desorption experiments on D2, H2 + Ag(111) more accurately than was possible with the SRP48 density functional for H2 + Cu(111). Also, the three new MS functionals describe the Cu, Ag, Au, and Pt metals more accurately than the all-purpose Perdew-Burke-Ernzerhof (PBE) functional. The only disadvantage we noted of the new MS functionals is that, as found for the example of H2 + Cu(111), the reaction barrier height obtained by taking weighted averages of the MS-PBEl and MS-RPBEl functionals is tunable over a smaller range (9 kJ/mol) than possible with the standard GGA PBE and RPBE functionals (33 kJ/mol). As a result of this restricted tunability, it is not possible to construct an SRP-DF for H2 + Ag(111) on the basis of the three examined MS meta-GGA functionals.

  View details for DOI 10.1021/acs.jpca.9b02914

  View details for Web of Science ID 000473251700024

  View details for PubMedID 31149824

  View details for PubMedCentralID PMC6600505

• Multi-ion Conduction in Li3OCl Glass Electrolytes JOURNAL OF PHYSICAL CHEMISTRY LETTERS Heenen, H. H., Voss, J., Scheurer, C., Reuter, K., Luntz, A. C. 2019; 10 (9): 2264–69

  Abstract

  Antiperovskite glasses such as Li3OCl and doped analogues have been proposed as excellent electrolytes for all-solid-state Li ion batteries (ASSB). Incorporating these electrolytes in ASSBs results in puzzling properties. This Letter describes a theoretical Li3OCl glass created by conventional melt-quench procedures. The ion conductivities are calculated using molecular dynamics based on a polarizable force field that is fitted to an extensive set of density functional theory-based energies, forces, and stresses for a wide range of nonequilibrium structures encompassing crystal, glass, and melt. We find high Li+ ion conductivity in good agreement with experiments. However, we also find that the Cl- ion is mobile as well so that the Li3OCl glass is not a single-ion conductor, with a transference number t + ≈ 0.84. This has important implications for its use as an electrolyte for all-solid-state batteries because the Cl could react irreversibly with the electrodes and/or produce glass decomposition during discharge-charge.

  View details for DOI 10.1021/acs.jpclett.9b00500

  View details for Web of Science ID 000466991300036

  View details for PubMedID 30995402

• Combining Experiment and Theory To Unravel the Mechanism of Two-Electron Oxygen Reduction at a Selective and Active Co-catalyst ACS CATALYSIS Bukas, V. J., Kim, H., Sengpiel, R., Knudsen, K., Voss, J., McCloskey, B. D., Luntz, A. C. 2018; 8 (12): 11940–51

  View details for DOI 10.1021/acscatal.8b02813

  View details for Web of Science ID 000453491100097

• Theoretical Investigations of the Electrochemical Reduction of CO on Single Metal Atoms Embedded in Graphene ACS CENTRAL SCIENCE Kirk, C., Section, L., Siahrostami, S., Karamad, M., Bajdich, M., Voss, J., Norskov, J. K., Chan, K. 2017; 3 (12): 1286–93

  Abstract

  Single transition metal atoms embedded at single vacancies of graphene provide a unique paradigm for catalytic reactions. We present a density functional theory study of such systems for the electrochemical reduction of CO. Theoretical investigations of CO electrochemical reduction are particularly challenging in that electrochemical activation energies are a necessary descriptor of activity. We determined the electrochemical barriers for key proton-electron transfer steps using a state-of-the-art, fully explicit solvent model of the electrochemical interface. The accuracy of GGA-level functionals in describing these systems was also benchmarked against hybrid methods. We find the first proton transfer to form CHO from CO to be a critical step in C1 product formation. On these single atom sites, the corresponding barrier scales more favorably with the CO binding energy than for 211 and 111 transition metal surfaces, in the direction of improved activity. Intermediates and transition states for the hydrogen evolution reaction were found to be less stable than those on transition metals, suggesting a higher selectivity for CO reduction. We present a rate volcano for the production of methane from CO. We identify promising candidates with high activity, stability, and selectivity for the reduction of CO. This work highlights the potential of these systems as improved electrocatalysts over pure transition metals for CO reduction.

  View details for PubMedID 29296669

  View details for PubMedCentralID PMC5746853

• Li+ Defects in a Solid-State Li Ion Battery: Theoretical Insights with a Li3OCl Electrolyte CHEMISTRY OF MATERIALS Stegmaier, S., Voss, J., Reuter, K., Luntz, A. C. 2017; 29 (10): 4330–40

  View details for DOI 10.1021/acs.chemmater.7b00659

  View details for Web of Science ID 000402498000022

• Pressure-induced structural, electronic, and optical evolution of hybrid perovskites Jaffe, A., Lin, Y., Beavers, C., Voss, J., Mao, W., Karunadasa, H. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569103603

• Hybrid perovskites under pressure: Accessing new properties through lattice compression Jaffe, A., Lin, Y., Umeyama, D., Beavers, C., Voss, J., Mao, W., Karunadasa, H. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569103671

• Hydrodeoxygenation of Phenol to Benzene and Cyclohexane on Rh(111) and Rh(211) Surfaces: Insights from Density Functional Theory JOURNAL OF PHYSICAL CHEMISTRY C Garcia-Pintos, D., Voss, J., Jensen, A. D., Studt, F. 2016; 120 (33): 18529–37

  View details for DOI 10.1021/acs.jpcc.6b02970

  View details for Web of Science ID 000382180000021

• Elucidating the electronic structure of supported gold nanoparticles and its relevance to catalysis by means of hard X-ray photoelectron spectroscopy SURFACE SCIENCE Reinecke, B. N., Kuhl, K. P., Ogasawara, H., Li, L., Voss, J., Abild-Pedersen, F., Nilsson, A., Jaramillo, T. F. 2016; 650: 24-33

  View details for DOI 10.1016/j.susc.2015.12.025

  View details for Web of Science ID 000377837800006

• mBEEF-vdW: Robust fitting of error estimation density functionals PHYSICAL REVIEW B Lundgaard, K. T., Wellendorff, J., Voss, J., Jacobsen, K. W., Bligaard, T. 2016; 93 (23)

  View details for DOI 10.1103/PhysRevB.93.235162

  View details for Web of Science ID 000378815500002

• High-pressure single-crystal structures of 3D lead-halide hybrid perovskites and pressure effects on their electronic and optical properties ACS Cent. Sci Jaffe, A., Lin, Y., Beavers, C. M., Voss, J., Mao, W. L., Karunadasa, H. I. 2016; 2: 201

  Abstract

  We report the first high-pressure single-crystal structures of hybrid perovskites. The crystalline semiconductors (MA)PbX3 (MA = CH3NH3 (+), X = Br(-) or I(-)) afford us the rare opportunity of understanding how compression modulates their structures and thereby their optoelectronic properties. Using atomic coordinates obtained from high-pressure single-crystal X-ray diffraction we track the perovskites' precise structural evolution upon compression. These structural changes correlate well with pressure-dependent single-crystal photoluminescence (PL) spectra and high-pressure bandgaps derived from density functional theory. We further observe dramatic piezochromism where the solids become lighter in color and then transition to opaque black with compression. Indeed, electronic conductivity measurements of (MA)PbI3 obtained within a diamond-anvil cell show that the material's resistivity decreases by 3 orders of magnitude between 0 and 51 GPa. The activation energy for conduction at 51 GPa is only 13.2(3) meV, suggesting that the perovskite is approaching a metallic state. Furthermore, the pressure response of mixed-halide perovskites shows new luminescent states that emerge at elevated pressures. We recently reported that the perovskites (MA)Pb(Br x I1-x )3 (0.2 < x < 1) reversibly form light-induced trap states, which pin their PL to a low energy. This may explain the low voltages obtained from solar cells employing these absorbers. Our high-pressure PL data indicate that compression can mitigate this PL redshift and may afford higher steady-state voltages from these absorbers. These studies show that pressure can significantly alter the transport and thermodynamic properties of these technologically important semiconductors.

  View details for DOI 10.1021/acscentsci.6b00055

  View details for PubMedCentralID PMC4850512

• Interfacial Challenges in Solid-State Li Ion Batteries JOURNAL OF PHYSICAL CHEMISTRY LETTERS Luntz, A. C., Voss, J., Reuter, K. 2015; 6 (22): 4599–4604

  View details for DOI 10.1021/acs.jpclett.5b02352

  View details for Web of Science ID 000365460700024

  View details for PubMedID 26551954

• From the Sabatier principle to a predictive theory of transition-metal heterogeneous catalysis JOURNAL OF CATALYSIS Medford, A. J., Vojvodic, A., Hummelshoj, J. S., Voss, J., Abild-Pedersen, F., Studt, F., Bligaard, T., Nilsson, A., Norskov, J. K. 2015; 328: 36-42

  View details for DOI 10.1016/j.jcat.2014.12.033

  View details for Web of Science ID 000356748300007

• Inherent Enhancement of Electronic Emission from Hexaboride Heterostructure PHYSICAL REVIEW APPLIED Voss, J., Vojvodic, A., Chou, S. H., Howe, R. T., Abild-Pedersen, F. 2014; 2 (2)

  View details for DOI 10.1103/PhysRevApplied.2.024004

  View details for Web of Science ID 000344331500001

• DFT Study of Atomically-Modified Alkali-Earth Metal Oxide Films on Tungsten JOURNAL OF PHYSICAL CHEMISTRY C Chou, S. H., Voss, J., Vojvodic, A., Howe, R. T., Abild-Pedersen, F. 2014; 118 (21): 11303-11309

  View details for DOI 10.1021/jp4120578

  View details for Web of Science ID 000336771700017

• Effects of d-band shape on the surface reactivity of transition-metal alloys PHYSICAL REVIEW B Xin, H., Vojvodic, A., Voss, J., Norskov, J. K., Abild-Pedersen, F. 2014; 89 (11)

  View details for DOI 10.1103/PhysRevB.89.115114

  View details for Web of Science ID 000332705300001

• Tunneling and Polaron Charge Transport through Li2O2 in Li-O-2 Batteries JOURNAL OF PHYSICAL CHEMISTRY LETTERS Luntz, A. C., Viswanathan, V., Voss, J., Varley, J. B., Norskov, J. K., Scheffler, R., Speidel, A. 2013; 4 (20): 3494-3499

  View details for DOI 10.1021/jz401926f

  View details for Web of Science ID 000326124500021

• Formation of heavy d-electron quasiparticles in Sr3Ru2O7 NEW JOURNAL OF PHYSICS Allan, M. P., Tamai, A., Rozbicki, E., Fischer, M. H., Voss, J., King, P. D., Meevasana, W., Thirupathaiah, S., Rienks, E., Fink, J., Tennant, D. A., Perry, R. S., Mercure, J. F., Wang, M. A., Lee, J., Fennie, C. J., Kim, E., Lawler, M. J., Shen, K. M., Mackenzie, A. P., Shen, Z., Baumberger, F. 2013; 15

  View details for DOI 10.1088/1367-2630/15/6/063029

  View details for Web of Science ID 000320698500003

• Thermionic current densities from first principles. journal of chemical physics Voss, J., Vojvodic, A., Chou, S. H., Howe, R. T., Bargatin, I., Abild-Pedersen, F. 2013; 138 (20): 204701-?

  View details for DOI 10.1063/1.4805002

  View details for PubMedID 23742494

• Thermionic current densities from first principles. journal of chemical physics Voss, J., Vojvodic, A., Chou, S. H., Howe, R. T., Bargatin, I., Abild-Pedersen, F. 2013; 138 (20): 204701-?

  Abstract

  We present a density functional theory-based method for calculating thermionic emission currents from a cathode into vacuum using a non-equilibrium Green's function approach. It does not require semi-classical approximations or crude simplifications of the electronic structure used in previous methods and thus provides quantitative predictions of thermionic emission for adsorbate-coated surfaces. The obtained results match well with experimental measurements of temperature-dependent current densities. Our approach can thus enable computational design of composite electrode materials.

  View details for DOI 10.1063/1.4805002

  View details for PubMedID 23742494

• An orbital-overlap model for minimal work functions of cesiated metal surfaces JOURNAL OF PHYSICS-CONDENSED MATTER Chou, S. H., Voss, J., Bargatin, I., Vojvodic, A., Howe, R. T., Abild-Pedersen, F. 2012; 24 (44)

  Abstract

  We introduce a model for the effect of cesium adsorbates on the work function of transition metal surfaces. The model builds on the classical point-dipole equation by adding exponential terms that characterize the degree of orbital overlap between the 6s states of neighboring cesium adsorbates and its effect on the strength and orientation of electric dipoles along the adsorbate-substrate interface. The new model improves upon earlier models in terms of agreement with the work function-coverage curves obtained via first-principles calculations based on density functional theory. All the cesiated metal surfaces have optimal coverages between 0.6 and 0.8 monolayers, in accordance with experimental data. Of all the cesiated metal surfaces that we have considered, tungsten has the lowest minimum work function, also in accordance with experiments.

  View details for DOI 10.1088/0953-8984/24/44/445007

  View details for Web of Science ID 000310571100009

  View details for PubMedID 23018485

• Density functional theory based screening of ternary alkali-transition metal borohydrides: A computational material design project JOURNAL OF CHEMICAL PHYSICS Hummelshoj, J. S., LANDIS, D. D., Voss, J., Jiang, T., Tekin, A., Bork, N., Dulak, M., Mortensen, J. J., Adamska, L., Andersin, J., Baran, J. D., Barmparis, G. D., Bell, F., Bezanilla, A. L., Bjork, J., Bjorketun, M. E., Bleken, F., Buchter, F., Burkle, M., Burton, P. D., Buus, B. B., Calborean, A., Calle-Vallejo, F., Casolo, S., Chandler, B. D., Chi, D. H., Czekaj, I., Datta, S., Datye, A., DELARIVA, A., Despoja, V., Dobrin, S., Engelund, M., Ferrighi, L., Frondelius, P., Fu, Q., FUENTES, A., Furst, J., Garcia-Fuente, A., Gavnholt, J., Goeke, R., Gudmundsdottir, S., Hammond, K. D., Hansen, H. A., Hibbitts, D., Hobi, E., Howalt, J. G., Hruby, S. L., Huth, A., Isaeva, L., Jelic, J., Jensen, I. J., Kacprzak, K. A., Kelkkanen, A., Kelsey, D., Kesanakurthi, D. S., Kleis, J., Klupfel, P. J., Konstantinov, I., Korytar, R., Koskinen, P., Krishna, C., Kunkes, E., Larsen, A. H., Lastra, J. M., Lin, H., Lopez-Acevedo, O., Mantega, M., Martinez, J. I., Mesa, I. N., Mowbray, D. J., Myrdal, J. S., Natanzon, Y., Nistor, A., Olsen, T., Park, H., Pedroza, L. S., Petzold, V., Plaisance, C., Rasmussen, J. A., Ren, H., Rizzi, M., Ronco, A. S., Rostgaard, C., Saadi, S., Salguero, L. A., Santos, E. J., Schoenhalz, A. L., Shen, J., Smedemand, M., Stausholm-Moller, O. J., Stibius, M., Strange, M., Su, H. B., Temel, B., Toftelund, A., Tripkovic, V., Vanin, M., Viswanathan, V., Vojvodic, A., Wang, S., Wellendorff, J., Thygesen, K. S., Rossmeisl, J., Bligaard, T., Jacobsen, K. W., Norskov, J. K., Vegge, T. 2009; 131 (1)

  Abstract

  We present a computational screening study of ternary metal borohydrides for reversible hydrogen storage based on density functional theory. We investigate the stability and decomposition of alloys containing 1 alkali metal atom, Li, Na, or K (M(1)); and 1 alkali, alkaline earth or 3d/4d transition metal atom (M(2)) plus two to five (BH(4))(-) groups, i.e., M(1)M(2)(BH(4))(2-5), using a number of model structures with trigonal, tetrahedral, octahedral, and free coordination of the metal borohydride complexes. Of the over 700 investigated structures, about 20 were predicted to form potentially stable alloys with promising decomposition energies. The M(1)(Al/Mn/Fe)(BH(4))(4), (Li/Na)Zn(BH(4))(3), and (Na/K)(Ni/Co)(BH(4))(3) alloys are found to be the most promising, followed by selected M(1)(Nb/Rh)(BH(4))(4) alloys.

  View details for DOI 10.1063/1.3148892

  View details for Web of Science ID 000267799100002

  View details for PubMedID 19586090

• Structural stability and decomposition of Mg(BH4)(2) isomorphs-an ab initio free energy study JOURNAL OF PHYSICS-CONDENSED MATTER Voss, J., Hummelshoj, J. S., Lodziana, Z., Vegge, T. 2009; 21 (1): 012203

  Abstract

  We present the first comprehensive comparison between free energies, based on a phonon dispersion calculation within density functional theory, of theoretically predicted structures and the experimentally proposed α (P6(1)) and β (Fddd) phases of the promising hydrogen storage material Mg(BH(4))(2). The recently proposed low-density [Formula: see text] ground state is found to be thermodynamically unstable, with soft acoustic phonon modes at the Brillouin zone boundary. We show that such acoustic instabilities can be detected by a macroscopic distortion of the unit cell. Following the atomic displacements of the unstable modes, we have obtained a new F 222 structure, which has a lower energy than all previously experimentally and theoretically proposed phases of Mg(BH(4))(2) and is free of imaginary eigenmodes. A new meta-stable high-density I4(1)/amd structure is also derived from the [Formula: see text] phase. Temperatures for the decomposition are found to be in the range of 400-470 K and largely independent of the structural complexity, as long as the primary cation coordination polyhedra are properly represented. This opens a possibility of using simple model structures for screening and prediction of finite temperature stability and decomposition temperatures of novel borohydride systems.

  View details for DOI 10.1088/0953-8984/21/1/012203

  View details for Web of Science ID 000261517500004

  View details for PubMedID 21817204

• Gamma-point lattice free energy estimates from O(1) force calculations JOURNAL OF CHEMICAL PHYSICS Voss, J., Vegge, T. 2008; 128 (18): 184708

  Abstract

  We present a new method for estimating the vibrational free energy of crystal (and molecular) structures employing only a single force calculation, for a particularly displaced configuration, in addition to the calculation of the ground state configuration. This displacement vector is the sum of the phonon eigenvectors obtained from a fast-relative to, e.g., density-functional theory (DFT)-Hessian calculation using interatomic potentials. These potentials are based here on effective charges obtained from a DFT calculation of the ground state electronic charge density but could also be based on other, e.g., empiric approaches.

  View details for DOI 10.1063/1.2919122

  View details for Web of Science ID 000255983500052

  View details for PubMedID 18532837

• Point defect dynamics in sodium aluminum hydrides - A combined quasielastic neutron scattering and density functional theory study Shi, Q., Voss, J., Jacobsen, H. S., Lefmann, K., Zamponi, M., Vegge, T. ELSEVIER SCIENCE SA. 2007: 469–73

  View details for DOI 10.1016/j.jallcom.2007.04.041

  View details for Web of Science ID 000250822900100

• Hydrogen dynamics in Na3AlH6: A combined density functional theory and quasielastic neutron scattering study JOURNAL OF PHYSICAL CHEMISTRY B Voss, J., Shi, Q., Jacobsen, H. S., Zamponi, M., Lefmann, K., Vegge, T. 2007; 111 (15): 3886–92

  Abstract

  Understanding the elusive catalytic role of titanium-based additives on the reversible hydrogenation of complex hydrides is an essential step toward developing hydrogen storage materials for the transport sector. Improved bulk diffusion of hydrogen is one of the proposed effects of doping sodium alanate with TiCl3, and here we study hydrogen dynamics in doped and undoped Na3AlH6 using a combination of density functional theory calculations and quasielastic neutron scattering. The hydrogen dynamics is found to be vacancy mediated and dominated by localized jump events, whereas long-range bulk diffusion requires significant activation. The fraction of mobile hydrogen is found to be small for both undoped and doped Na3AlH6, even at 350 K, and improved hydrogen diffusion as a result of bulk-substituted titanium is found to be unlikely. We also propose that previously detected low-temperature point defect motion in sodium alanate could result from vacancy-mediated sodium diffusion.

  View details for DOI 10.1021/jp0667036

  View details for Web of Science ID 000245635100005

  View details for PubMedID 17388555