Authors: Maytal Caspary Toroker | Michele Pavone
Source: Advanced Theory and Simulations (article, 2023-10-01)
Field: Materials Science — Materials Chemistry

Editorial for the Special Issue on “Computational Materials Science” The collection of articles featured in this special issue “Computational Materials Science” are meant to showcase the progress in the field of modeling nanocrystal catalysts. Most of the authors featured in this issue are members of COST Action CA18234 “Computational materials sciences for efficient water splitting with nanocrystals from abundant elements”, which is a European network of experts in computational modeling of nanostructured materials and catalysis. The purpose of this action is to connect methods at different length and time scales and integrate all of them within a united framework for modeling the complex features of nanostructured and reactive materials. This special issue presents the current status and the most recent research progress in reaching the ambitious goal of an effective and reliable first-principles and multi-scale modeling for nanostructured catalysts. In the following a short overview of the main results in the collected contributions. 1. Pourbaix diagrams can be used to provide information on thermodynamically stable surfaces under certain conditions of pH and potential U, which is critical for starting building the surface model. In a paper by Kai S. Exner, Francesc Illas, and co-workers (article 2200217), a detailed analysis is provided on how to build the diagrams from density functional theory (DFT) calculations. The diagrams for a series of MXenes are provided, including Ti2C, Ti3C2, V2C, and Mo2C with single and double mixed terminations involving O, OH, H, or F surface groups. The Pourbaix diagrams for all explored MXenes exhibit similar trends in the predicted stable surface coverage at different values of pH and U. In aqueous environment, MXenes will not show their bare surface at any pH-U working conditions. The authors have shown that depending on the pH and U conditions, other terminations rather than the typically assumed fully O* or fully OH* covered surfaces should be considered. In particular, the fully H* terminated surface is of importance for U < –0.6 V versus SHE. Mixed surface phases involving –F moieties with –O or –OH groups can also appear such as in the case of Ti2C and Ti3C at strong acidic conditions and slightly negative potentials of –0.6 V < U versus SHE < 0 V, which are of relevance to the hydrogen evolution reaction (HER). 2. The choice of the approximate XC functional is an important step for modeling oxygen evolution reaction (OER) and HER catalysis. In a paper by Gianfranco Pacchioni and co-workers (article 2200513), the role of the XC functional was demonstrated on single atom catalysis for 16 transition metal atoms embedded in N-doped graphene. The use of Perdew–Burke–Ernzerhof (PBE) that is commonly adopted to study single atom catalysis appears acceptable for 4d and 5d metals, while in the case of 3d systems PBE+U or PBE0 approaches are recommended, in particular for magnetic ground states. There is not only a quantitative problem in reproducing the Gibbs free energies, but also a qualitative difference, with some SACs that are predicted to be very active at the PBE level and totally inactive using the PBE0 hybrid functional. 3. What is the best method to address the materials and redox processes for effective oxidation of saltwater? To answer this question, Robert B. Wexler and Emily A. Carter (article 2200592) report a benchmark study based on DFT and least-squares linear regression on the O, Cl, and H chemisorption enthalpy trends and scaling on 3d transition metals, Pd, and Pt in the face-centered cubic (fcc) and their ground-state crystal structures. This work present a wealth of results with different DFT methods on systems that are relevant for seawater electrolysis. Beside the importance of selecting the proper methods to address these materials/processes, the authors prove that the O and Cl chemisorption enthalpies are strongly correlated, suggesting that the transition metals considered will oxidize unselectively water and Cl−. This strong correlation appears also for crystal reduction potentials of binary oxides and chlorides, indicating a fundamental challenge for future seawater electrode materials design. 4. Chemical models of complex processes involve several chemical reactions and parameters that hold some uncertainty. Sensitivity analysis is key tool to quantify and trace this uncertainty to specific input parameters. In this context, Anja Bieberle-Hütter and co-workers (article 2200615) present a work on the implementation and validation of the Sobol's global variance-based sensitivity analysis method, which can be set-up for microkinetic modeling and can easily be applied for different models. Such analysis framework is successfully demonstrated by means of two case studies: CO oxidation and OER at the photoanode in a photo-electrochemical cell. The reported results also highlight the influence of each input parameter on the output uncertainty, for example for the OER the most relevant are the catalyst valence band potential and the solvent reorganization energy. Such approach holds great potential to be integrated with atomistic tools for multiscale modelling of complex catalytic materials and processes. 5. Reactivity at a transition metal surface can be strongly affected by the exposed facets and surface steps. Eugene Kotomin and co-worker (article 2200619) present a first-principles study on photocatalytic activity toward water splitting of strontium titanate SrTiO3 (STO) and how it can be further enhanced on multifaceted nanoparticles. With periodic DFT calculations on water adsorption and proton diffusion the authors report new insights on the thermodynamics of the HER within the framework of computational hydrogen electrode, highlighting how surface morphology can impact catalytic activity toward water splitting, with flat surfaces providing best catalytic activity toward formation of molecular hydrogen. 6. One of the great obstacles for theoretical characterization is how to calculate the activation energy during heterogeneous catalysis. Usually, due to large computational time, calculations of kinetic activation barriers are avoided and catalysis is evaluated based on thermodynamic adsorption energies. In a paper by Nadav Snir and Maytal Caspary Toroker (article 2300182), a new method is suggested for calculating the inner sphere component of the reorganization energy that contributes to the activation energies. The algorithm is based on Marcus theory combined with the climbing image nudged elastic band method, which allows the calculation of the activation energy at different potentials and without simulating solvation in order to obtain the inner sphere component alone arising from the reorganization of the ionic surface. The method is simple to use and can be adopted to evaluate activation energies and to determine the rate limiting step. 7. Multiscale modeling is necessary for more realistic assessment of nanomaterials with subtle structural modifications. José R. B. Gomes and co-workers (article 2200628) presented a review with techniques that range from quantum mechanical approaches based on DFT to classical atomistic and coarse-grained force field methods as well as machine learning. Several material test cases are presented including: MOFs, LDHs, and MXenes. 8. Extended surface models retain the common flaw of lacking proper description of finite-size effects in nanostructure systems. To address this issue, Angel Morales and co-worker (article 2200670) report a relativistic, all-electron, non-periodic DFT study on the interaction between a metal cluster and a metal-oxide nanoparticle substrate. This work provides a neat example on the relevance of large model to describe realistic nanostructured catalysts. The Ru13 cluster supported on an octahedral anatase (TiO2)84 nanoparticle is used as case study. The formation of the metal/anatase heterostructure leads to a decrease of the energy gap inherent to the bare anatase nanoparticle, with the contribution of partially filled Ru 4d orbitals with Kohn–Sham energies in the same energy range of O 2p occupied and Ti 3d empty manifolds. This feature is systematic, no matter the interaction involves the oxide nanoparticle facet or edge regions. This study constitutes a first step in designing a strategy to investigate metal-semiconductor nanostructures using realistic models that go beyond the use of extended surfaces. 9. Multi-ferroic oxides show promising activity as photocatalyst for their peculiar opto-electronic properties: Bismuth Ferrite is the protypical solid of this class of materials, but further optimization of its properties are needed for an optimal catalytic efficiency. Ricardo Grau-Crespo and co-worker (article 2200673) report a DFT study on the BiCoxFe1−xO3 (x = 0; 0.0625; 0.125) solid solutions, with the aim of investigating how Co substitution at Fe site can be useful in engineering the band gap and band alignment, without losing the ferroelectric properties. The results based on bulk and surface DFT calculations and on Monte Carlo simulations of defect interaction and segregation provide a complete overview of the thermodynamic and electronic properties of the proposed solid solutions. 10. Charge transport via interfaces in materials is crucial in comprehending the constraints of many electronic devices, including electrocatalysis. Nonetheless, simulating experimental length scale structures puts a challenge in terms of computational efforts. In the work by Yair Reichman and Maytal Caspary Toroker (article 2300155), several heterostructure systems of typical semiconductors with zinc-blende unit cells were investigated. The study analyzed the correlation between the transmission coefficient of the one-electron wave function to pass through the interface and interface characteristic parameters. As demonstrated for zinc-blende structure materials under strain, the primary conclusion is that the parameters of the material's potential can be used to predict the transmission coefficient of the electronic wave function even when the potential has a complex realistic curvature. Overall, the main results from this collection of papers can be sum up in a simple message: further advances in this field call for improving the accuracy of each method (such as choosing a proper exchange-correlation function in DFT calculations) and, at the same time, combining complementary models at different scales. As the majority of the community is performing DFT calculations with continuous effort, the effective and consistent overlap between DFT and MD simulations is a first good step to improve over standard 0 K DFT calculations. The next pressing issues in catalytic design is to account for the complex nanoscale architecture of heterogeneous functional interfaces along with the necessary solvent environment. Thus, multiscale modeling with mixed methodologies is anticipated to be the required avenue to tackle such ambitious goal. Eventually, as guest editors, we are grateful to all the authors who contributed to this special issue and would like to express our appreciation especially to Dr. Stefan Spiegel, the editor-in-chief of Advanced Theory and Simulations, for providing the platform to demonstrate and showcase the latest progress in computational materials science research from a group of motivated scientists with a strong expertise in the area of nanocrystal catalysis that joined their efforts to build a common COST action network. Maytal Caspary Toroker received a Ph.D. in chemistry from the Technion Israel Institute of Technology in 2009. After spending a postdoctoral fellowship at Princeton University, Prof. Caspary Toroker built an independent research group at the Department of Materials Science and Engineering at the Technion in 2013. The research group has experience with quantum computation for understanding material behaviour at surfaces and interfaces, specializing in combining Density Functional theory, particular heterogenous catalysis in solid state material surfaces, and quantum dynamics for charge transport calculations. The group has strong background in computational and theoretical tools to study metallic and semiconducting materials for electricity, fuels, and solar applications. Prof. Caspary Toroker is responsible for several national and European projects including holding Chair of CA18234 COST Action. Michele Pavone received the Ph.D. in Chemical Sciences in 2007 from University of Naples Federico II in Italy. After postdoctoral fellowship at Princeton University (USA) in the group of Prof. Emily Carter, Michele Pavone started his independent research group at the Department of Chemical Sciences at the University of Naples Federico II where he is now Associate Professor of Physical Chemistry. Prof. Pavone research group is active in the field of computational chemistry and materials sciences with a specific focus on development and application of ab initio approaches to physico-chemical processes in heterogeneous functional interfaces for energy conversion and storage. Prof. Pavone is responsible for several national and European projects (including a Vice-Chair role in the EU COST Action 18 234), and his research achievements have been recognized with several awards from the Italian Chemical Society. Pourbaix diagram ; MXenes ; Action (physics) ; Nanotechnology ; Scale (ratio) ; Computer science ; Field (mathematics) ; Materials science ; Chemistry ; Mathematics ; Physics ; Physical chemistry MXene and MAX Phase Materials ; Nanomaterials for catalytic reactions ; Catalysis and Hydrodesulfurization Studies