Using G0W0G_0W_0 Level Alignment to Identify Catechol's Structure on TiO2_2(110)

We perform state-of-the-art calculations for a prototypical dye sensitized solar cell: catechol on rutile TiO$_2$(110). Catechol is often used as an anchoring group for larger more complex organic and inorganic dyes on TiO$_2$ and forms a type II heterojunctions on TiO$_2$(110). In particular, we compare quasiparticle (QP) $G_0W_0$ with hybrid exchange correlation functional (HSE) density functional theory (DFT) calculations for the catechol-rutile TiO$_2$(110) interface. In so doing, we provide a theoretical interpretation of ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) experiments for this prototypical system. Specifically, we demonstrate that the position, presence, and intensity of peaks associated with catechol's HOMO, intermolecular OH$-$O bonds, and interfacial hydrogen bonds to the surface bridging O atoms (O$_{br}$H$-$C and O$_{br}$H$-$O) may be used to fingerprint deprotonation of catechol's OH anchoring groups. Furthermore, our results suggest deprotonation of these groups, while being nearly isoenergetic at high coverages, may significantly increase the photovoltaic efficiency of catechol$-$TiO$_2$(110) interfaces.Comment: 7 pages, 4 figures, corrected table

Coverage Dependence of the Level Alignment for Methanol on TiO2_2(110)

Electronic level alignment at the interface between an adsorbed molecular layer and a semiconducting substrate determines the activity and efficiency of many photocatalytic materials. We perform $G_0W_0$ calculations to determine the coverage dependence of the level alignment for a prototypical photocatalytic interface: 1/2 and 1 monolayer (ML) intact and dissociated CH$_3$OH on rutile TiO$_2$(110). We find changes in the wavefunction's spatial distribution, and a consequent renormalization of the quasiparticle energy levels, as a function of CH$_3$OH coverage and dissociation. Our results suggest that the occupied molecular levels responsible for hole trapping are not those observed in the ultraviolet photoemission spectroscopy (UPS) spectrum. Rather, they are those of isolated CH$_3$O on the surface. We find the unoccupied molecular levels have either 2D character with weight above the surface at 1 ML coverage, or significant hybridization with the surface at 1/2 ML coverage. These results suggest the resonance observed in the two photon phooemission (2PP) spectrum arises from excitations to unoccupied "Wet electron" levels with 2D character.Comment: 8 pages, 5 figures, 1 tabl

Las métricas de investigación y su uso responsable

Universidad Pablo de Olavid

Comparing quasiparticle H2_2O level alignment on anatase and rutile TiO2_2

Knowledge of the molecular frontier levels' alignment in the ground state can be used to predict the photocatalytic activity of an interface. The position of the adsorbate's highest occupied molecular orbital (HOMO) levels relative to the substrate's valence band maximum (VBM) in the interface describes the favorability of photogenerated hole transfer from the VBM to the adsorbed molecule. This is a key quantity for assessing and comparing H$_2$O photooxidation activities on two prototypical photocatalytic TiO$_2$ surfaces: anatase (A)-TiO$_2$(101) and rutile (R)-TiO$_2$(110). Using the projected density of states (DOS) from state-of-the-art quasiparticle (QP) $G_0W_0$ calculations, we assess the relative photocatalytic activity of intact and dissociated H$_2$O on coordinately unsaturated (Ti$_{\textit{cus}}$) sites of idealized stoichiometric A-TiO$_2$(101)/R-TiO$_2$(110) and bridging O vacancies (O$_{\textit{br}}^{\textit{vac}}$) of defective A-TiO$_{2-x}$(101)/R-TiO$_{2-x}$(110) surfaces ($x=\frac{1}{4},\frac{1}{8}$) for various coverages. Such a many-body treatment is necessary to correctly describe the anisotropic screening of electron-electron interactions at a photocatalytic interface, and hence obtain accurate interfacial level alignments. The more favorable ground state HOMO level alignment for A-TiO$_2$(101) may explain why the anatase polymorph shows higher photocatalytic activities than the rutile polymorph. Our results indicate that (1) hole trapping is more favored on A-TiO$_2$(101) than R-TiO$_2$(110) and (2) HO@Ti$_{\textit{cus}}$ is more photocatalytically active than intact H$_2$O@Ti$_{\textit{cus}}$

Level alignment of a prototypical photocatalytic system: Methanol on TiO2(110)

Photocatalytic and photovoltaic activity depends on the optimal alignment of electronic levels at the molecule/semiconductor interface. Establishing level alignment experimentally is complicated by the uncertain chemical identity of the surface species. We address the assignment of the occupied and empty electronic levels for the prototypical photocatalytic system of methanol on a rutile TiO2 (110) surface. Using many-body quasiparticle (QP) techniques we show that the frontier levels measured in ultraviolet photoelectron and two photon photoemission spectroscopy experiments can be assigned with confidence to the molecularly chemisorbed methanol, rather than its decomposition product, the methoxy species. We find the highest occupied molecular orbital (HOMO) of the methoxy species is much closer to the valence band maximum, suggesting why it is more photocatalytically active than the methanol molecule. We develop a general semi-quantitative model for predicting many-body QP energies based on the appropriate description of electronic screening within the bulk, molecular or vacuum regions of the wavefunctions at molecule/semiconductor interfaces.Comment: 5 pages, 5 figure

Quasiparticle level alignment for photocatalytic interfaces

arXiv:1404.5166v1Electronic level alignment at the interface between an adsorbed molecular layer and a semiconducting substrate determines the activity and efficiency of many photocatalytic materials. Standard density functional theory (DFT)-based methods have proven unable to provide a quantitative description of this level alignment. This requires a proper treatment of the anisotropic screening, necessitating the use of quasiparticle (QP) techniques. However, the computational complexity of QP algorithms has meant a quantitative description of interfacial levels has remained elusive. We provide a systematic study of a prototypical interface, bare and methanol-covered rutile TiO2(110) surfaces, to determine the type of many-body theory required to obtain an accurate description of the level alignment. This is accomplished via a direct comparison with metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), and two-photon photoemission (2PP) spectroscopy. We consider GGA DFT, hybrid DFT, and G0W0, scQPGW1, scQPGW0, and scQPGW QP calculations. Our results demonstrate that G0W0, or our recently introduced scQPGW1 approach, are required to obtain the correct alignment of both the highest occupied and lowest unoccupied interfacial molecular levels (HOMO/LUMO). These calculations set a new standard in the interpretation of electronic structure probe experiments of complex organic molecule/semiconductor interfaces.We acknowledge funding from the European Projects DYNamo (No. ERC-2010- AdG-267374), and CRONOS (No. 280879-2 CRONOS CPFP7); Spanish Grants (Nos. FIS2012-37549-C05-02, FIS2010-21282-C02-01, PIB2010US-00652, RYC-2011-09582, JAE DOC, JCI-2010-08156); Grupos Consolidados UPV/EHU del Gobierno Vasco (No. IT-319-07); NSFC (Nos. 21003113 and 21121003); MOST (No. 2011CB921404); and NSF Grant No. CHE-1213189.Peer Reviewe

Phosphorus-Doped Graphene as a Metal-Free Material for Thermochemical Water Reforming at Unusually Mild Conditions

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Sustainable Chemistry & Engineering, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acssuschemeng.8b04462"[EN] P-doped graphene (Phy-G) prepared by pyrolysis of phytic acid at 900 degrees C under inert atmosphere has been evaluated as a metal-free catalyst for the thermochemical water splitting. XPS, solid-state P-31 NMR, and Raman spectroscopy confirm the presence of P atoms bonded to C atoms in the graphene lattice as well as some oxygenated P groups, such as phosphates or phosphonates. HRTEM and AFM images show the characteristic sheet morphology of 2D graphene materials of several micrometers lateral size and exhibiting a high crystallinity with the characteristic hexagonal arrangement of graphenic materials. Phy-G has been submitted to consecutive oxidation/activation thermochemical cycles at 650 and 800 degrees C under H2O-saturated Ar and dry Ar atmospheres, respectively. During the oxidation periods, H-2 evolution up to 21.6 mu mol/min.g was measured. However, no O-2 evolves in the activation steps. Experimental evidence and computational calculations support the formation of P=O bonds during the oxidation steps. The computational calculations suggest that the thermocatalytic H2O splitting occurs on the P atoms of doped graphene through a stepwise process involving an intermediate with a P-OH group and a H attached to a neighboring C atom and subsequent H-2 evolution, leading to the formation of P-O bonds.J.A. and H.G. give thanks for the financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa SEV2016-0683, GRAPAS, and CTQ2015-69563-CO2-1) and Generalitat Valenciana (Prometeo 2017-083). J.A. also thanks UPV for a postdoctoral scholarship. A.V. is grateful to the National Plan for Scientific and Technical Research and Innovation 2013-2016 (ENE2015-71254-C3-2-R) since part of this work has been carried out within the ARROPAR-CEX project. L.B. and A.M. give thanks for the financial support from the Ministry of Economy and Competitiveness (CTQ2015-69363-P). We thank Mr. Pere Creus for carrying out some of the calculations. A.M. gives thanks for the financial support from the Departament d'Innovacio, Universitats i Empresa (DIUE), Generalitat de Catalunya (Project 2017SGR348). Calculations were carried out at the Red Espanola de Supercomputacion (Projects QCM-2017-3-0038 and QCM-2018-1-0037).Albero-Sancho, J.; Vidal, A.; Migani, A.; Concepción Heydorn, P.; Blancafort, L.; García Gómez, H. (2019). Phosphorus-Doped Graphene as a Metal-Free Material for Thermochemical Water Reforming at Unusually Mild Conditions. ACS Sustainable Chemistry & Engineering. 7(1):838-846. https://doi.org/10.1021/acssuschemeng.8b04462S8388467

Early events in the photochemistry of 5-diazo Meldrum's acid : Formation of a product manifold in C-N bound and pre-dissociated intersection seam regions

5-Diazo Meldrum's acid (DMA) undergoes a photo-induced Wolff rearrangement (WR). Recent gas-phase experiments have identified three photochemical products formed in a sub-ps scale after irradiation, a carbene formed after nitrogen loss, a ketene formed after WR and a second carbene formed after nitrogen and CO elimination (A. Steinbacher, et al. Phys. Chem. Chem. Phys., 2014, 16, 7290-7298). In this work, ground- and excited-state potential energy surfaces (PESs) have been investigated at the MS-CASPT2// CASSCF level. The key element of the PESs is an extended S0/S1 conical intersection seam along the C-N dissociation coordinate. The C-N predissociated region of the seam is accessed after excitation to the bright S2 state, and decay paths from the seam to the three primary products have been characterized. For the ketene and carbene II products, we show two possible formation pathways, a direct and a stepwise one, which suggests that these products may be formed in a bi-modal fashion. We have also characterized two possible mechanisms for triplet formation, one occurring before C-N dissociation involving a (S1/T2/T1) crossing region, and another one through the carbene. In contrast, excitation to S1 leads to a C-N bound region of the seam from where DMA regeneration or diazirine formation is possible, with a preference for the first case. The results are in good agreement with experimental data. Together with our previous work on diazonaphthoquinone, they show the importance of an extended seam in the photochemistry of a-diazoketones

Quasiparticle level alignment for photocatalytic interfaces

Electronic level alignment at the interface between an adsorbed molecular layer and a semiconducting substrate determines the activity and efficiency of many photocatalytic materials. Standard density functional theory (DFT)-based methods have proven unable to provide a quantitative description of this level alignment. This requires a proper treatment of the anisotropic screening, necessitating the use of quasiparticle (QP) techniques. However, the computational complexity of QP algorithms has meant a quantitative description of interfacial levels has remained elusive. We provide a systematic study of a prototypical interface, bare and methanol-covered rutile TiO(110) surfaces, to determine the type of many-body theory required to obtain an accurate description of the level alignment. This is accomplished via a direct comparison with metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), and two-photon photoemission (2PP) spectroscopy. We consider GGA DFT, hybrid DFT, and GW, scQPGW1, scQPGW, and scQPGW QP calculations. Our results demonstrate that GW, or our recently introduced scQPGW1 approach, are required to obtain the correct alignment of both the highest occupied and lowest unoccupied interfacial molecular levels (HOMO/LUMO). These calculations set a new standard in the interpretation of electronic structure probe experiments of complex organic molecule/semiconductor interface