Author: Ageo Meier de Andrade
This thesis is built around two pillars. One is heterogeneous catalysis in the broader context of green chemistry. The focus here is on identifying catalytically active materials suitable for the valorization of renewable feedstocks. The second pillar deals with materials modelling itself, both its role to help identify the features responsible for certain desired material properties and the assessment of model quality and how to overcome challenges when modelling complex systems.
Density functional theory (DFT) has become a standard method in heterogeneous catalysis and materials science, as it generally combines good accuracy with an affordable computational cost. The choice of density functional (in relation to the system under study) strongly affect the accuracy of the DFT results. In this thesis, a subset of functionals have been tested and validated with respect to their ability to predict structural and energetic properties of single- and multi-component materials. It is shown that the inclusion of dispersion corrections by computing the nonlocal correlation self-consistently, as done in the vdW-DF-cx functional, increases the accuracy of computed results in relation to experimental data.
In the evaluation of the functionals, the computed properties were rationalized in terms of (i) the reduced density gradient distribution, unique for each material, and (ii) the exchange enhancement factor, unique for each density functional and dependent on the reduced density gradient distribution. Moreover, a tool is presented that can guide researchers towards the most appropriate density functional for the problem in question. This involves a protocol that brings DFT results into better agreement with experiment.
Heterogeneous catalysts are complex and catalyst research is often performed using model experiments and calculations. Here descriptors have important roles to play. Two descriptors for catalytic activity have been scrutinized in this thesis. The first is the work function of metal surfaces. Here, it is shown that the adsorption of selected ad-atoms on Ni surfaces provides a route to control the metal’s work function over a wide energy range. The second descriptor is the difference in stability between the enol and keto tautomers of a model lignin molecule on a model metal catalyst surface in the context of lignin depolymerization. The aim is to explore the reasons underlying the relative stabilities and to enhance the preference for enol in the keto-to-enol tautomerization. The modelling results show that a mixed PdPt alloy surface stabilizes the enol tautomer, suggesting that this could be an active catalyst for lignin depolymerization.
Doctorate thesis, Acta Universitatis Upsaliensis, 2021. , p. 74
Authors: Ageo Meier de Andrade, Jolla Kullgren, and Peter Broqvist
This work reports on the performance of density functional theory (DFT) for a series of single and binary systems, aiming for a quantitative description of NiX (X=C, Si, Ge, and Sn) alloys. Both semilocal GGA and a meta-GGA density functional, with and without dispersion corrections, are tested. We found in our study that no single functional simultaneously provides an accurate quantitative description of the investigated structural and energetic properties. However, the spread in computed DFT data could be rationalized in terms of the distribution of reduced density gradients and differences in the evolution of the exchange enhancement factors for different functionals. We demonstrate how to construct a regression model based on data from several density functionals that increases the predictivity of semilocal DFT. We foresee that the use of regression models (or extensions of it) can be valuable in the development of more accurate density functionals that in the future could provide a quantitative accuracy for complex multicomponent systems.
Phys. Rev. B 105, 085127 (2022)
Authors: Yocefu Hattori, Jie Meng, Kaibo Zheng, Ageo Meier de Andrade, Jolla Kullgren, Peter Broqvist, Peter Nordlander, and Jacinto Sá
Plasmonic materials have optical cross sections that exceed by 10-fold their geometric sizes, making them uniquely suitable to convert light into electrical charges. Harvesting plasmon-generated hot carriers is of interest for the broad fields of photovoltaics and photocatalysis; however, their direct utilization is limited by their ultrafast thermalization in metals. To prolong the lifetime of hot carriers, one can place acceptor materials, such as semiconductors, in direct contact with the plasmonic system. Herein, we report the effect of operating temperature on hot electron generation and transfer to a suitable semiconductor. We found that an increase in the operation temperature improves hot electron harvesting in a plasmonic semiconductor hybrid system, contrasting what is observed on photodriven processes in nonplasmonic systems. The effect appears to be related to an enhancement in hot carrier generation due to phonon coupling. This discovery provides a new strategy for optimization of photodriven energy production and chemical synthesis.
Nano Lett. 2021, 21, 2, 1083–1089
Authors: Ageo Meier de Andrade, Pemikar Srifa, Peter Broqvist, and Kersti Hermansson
It has been suggested in the literature that keto‐to‐enol tautomerization plays a vital role for lignin fragmentation under mild conditions. On the other hand, previous modelling has shown that the adsorbed keto form is more stable than enol on the Pd(111) catalyst. The current density functional theory study of lignin model molecules shows that, in the gas‐phase, keto is more stable than enol, but on the Pd surface, we find enol conformers that are at least as stable as keto. This supports the experimental result that the favourable reaction pathway for lignin depolymerization involves keto‐enol tautomerization. An energy decomposition analysis gives insights concerning the origin of the fine energy balance between the keto and enol forms, where the molecule–surface interaction (−7 eV) and the molecular strain energy (+3 eV) are the main contributors to the adsorption energy.
ChemSusChem, 2020, 13, 6574-6581
Authors: Ageo Meier de Andrade, Jolla Kullgren and Peter Broqvist
We evaluate the qualitative and quantitative accuracy of various flavors of density functionals with and without accounting for dispersion corrections. Our test system is nickel in the form of bulk, surfaces, and nanoparticles for which we compute structural properties, bulk cohesive energies, surface energies, and work functions and compare to experimental data. We find that the inclusion of any dispersion, either by an a posteriori correction or by a self-consistent treatment by explicitly computing the nonlocal correlation contribution to the total energy, has a significant effect on the calculated properties and improves the quantitative comparison to experiments. Besides the quantitative agreement, we also investigate qualitative features by comparing Wulff shapes of metal nanoparticles as obtained using the different density functionals. We find that all tested functionals predict similar Wulff shapes for nickel nanoparticles but still have some small differences. These results show that the relative energies calculated using the semilocal GGA and meta-GGA functionals, with and without dispersion, are quite similar. Our findings can also be generalized to other systems when rationalized in terms of the computed reduced density gradients. We find that the distribution of reduced density gradients in a material is correlated to the steepness of the exchange enhancement factor and propose that this information can be used as a quantitative guide when it comes to picking the most appropriate density functional for specific target systems as well as when it comes to extrapolating DFT data to predict experiments.
Phys. Rev. B 102, 2020, 075115