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Register a new userReaction energetics of Hydrogen on the Si(100) surface: A periodic many-electron theory study
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Added by
Theodoros Tsatsoulis
Publication date
2018
fields
Physics
and research's language is
English
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We report on a many-electron wavefunction theory study for the reaction energetics of hydrogen dissociation on the Si(100) surface. We demonstrate that quantum chemical wavefunction based methods using periodic boundary conditions can predict chemically accurate results for the activation barrier and the chemisorption energy in agreement with experimental findings. These highly accurate results for the reaction energetics enable a deeper understanding of the underlying physical mechanism and make it possible to benchmark widely used density functional theory methods.
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We evaluate the electronic, geometric and energetic properties of quasi 1-D wires formed by dangling bonds on Si(100)-H (2 x 1). The calculations are performed with density functional theory (DFT). Infinite wires are found to be insulating and Peierls distorted, however finite wires develop localized electronic states that can be of great use for molecular-based devices. The ground state solution of finite wires does not correspond to a geometrical distortion but rather to an antiferromagnetic ordering. For the stability of wires, the presence of abundant H atoms in nearby Si atoms can be a problem. We have evaluated the energy barriers for intradimer and intrarow diffusion finding all of them about 1 eV or larger, even in the case where a H impurity is already sitting on the wire. These results are encouraging for using dangling-bond wires in future devices.
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The CO_{2} electro-reduction reaction (CORR) is a promising avenue to convert greenhouse gases into high-value fuels and chemicals, in addition to being an attractive method for storing intermittent renewable energy. Although polycrystalline Cu surfaces have long known to be unique in their capabilities of catalyzing the conversion of CO_{2} to higher-order C1 and C2 fuels, such as hydrocarbons (CH_{4}, C_{2}H_{4} etc.) and alcohols (CH_{3}OH, C_{2}H_{5}OH), product selectivity remains a challenge. In this study, we select three metal catalysts (Pt, Au, Cu) and apply in situ surface enhanced infrared absorption spectroscopy (SEIRAS) and ambient-pressure X-ray photoelectron spectroscopy (APXPS), coupled to density-functional theory (DFT) calculations, to get insight into the reaction pathway for the CORR. We present a comprehensive reaction mechanism for the CORR, and show that the preferential reaction pathway can be rationalized in terms of metal-carbon (M-C) and metal-oxygen (M-O) affinity. We show that the final products are determined by the configuration of the initial intermediates, C-bound and O-bound, which can be obtained from CO_{2} and (H)CO_{3}, respectively. C1 hydrocarbons are produced via OCH_{3, ad} intermediates obtained from O-bound CO_{3, ad} and require a catalyst with relatively high affinity for O-bound intermediates. Additionally, C2 hydrocarbon formation is suggested to result from the C-C coupling between C-bound CO_{ad} and (H)CO_{ad}, which requires an optimal affinity for the C-bound species, so that (H)CO_{ad} can be further reduced without poisoning the catalyst surface. Our findings pave the way towards a design strategy for CORR catalysts with improved selectivity, based on this experimental/theoretical reaction mechanisms that have been identified.
We report a detailed study of surface and interface properties of pulsed-laser deposited NiMnSb films on Si (100) substrate as a function of film thickness. As the thickness of films is reduced below 35 nm formation of a porous layer is observed. Porosity in this layer increases with decrease in NiMnSb film thickness. These morphological changes of the ultra thin films are reflected in the interesting transport and magnetic properties of these films. On the other hand, there are no influences of compositional in-homogeneity and surface/interface roughness on the magnetic and transport properties of the films.
We present a detailed study of the energetics of water clusters (H$_2$O)$_n$ with $n le 6$, comparing diffusion Monte Carlo (DMC) and approximate density functional theory (DFT) with well converged coupled-cluster benchmarks. We use the many-body decomposition of the total energy to classify the errors of DMC and DFT into 1-body, 2-body and beyond-2-body components. Using both equilibrium cluster configurations and thermal ensembles of configurations, we find DMC to be uniformly much more accurate than DFT, partly because some of the approximate functionals give poor 1-body distortion energies. Even when these are corrected, DFT remains considerably less accurate than DMC. When both 1- and 2-body errors of DFT are corrected, some functionals compete in accuracy with DMC; however, other functionals remain worse, showing that they suffer from significant beyond-2-body errors. Combining the evidence presented here with the recently demonstrated high accuracy of DMC for ice structures, we suggest how DMC can now be used to provide benchmarks for larger clusters and for bulk liquid water.
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