Deriving accurate work functions from thin-slab calculations

The electronic band gap is a fundamental material parameter requiring control for light harvesting, conversion and transport technologies, including photovoltaics, lasers and sensors. Although traditional methods to tune band gaps rely on chemical alloying, quantum size effects, lattice mismatch or superlattice formation, the spectral variation is often limited to o1 eV, unless marked changes to composition or structure occur. Here we report large band gap changes of up to 200% or B2 eV without modifying chemical composition or use of epitaxial strain in the LaSrAlO 4 Ruddlesden-Popper oxide. First-principles calculations show that ordering electrically charged [LaO] 1 þ and neutral [SrO] 0 monoxide planes imposes internal electric fields in the layered oxides. These fields drive local atomic displacements and bond distortions that control the energy levels at the valence and conduction band edges, providing a path towards electronic structure engineering in complex oxides.

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“…In Fig. 2, we show the macroscopically averaged 32,33 Fig. 1), which occur to minimize the interatomic forces for a given Z in LaSrAlO 4 .…”

Section: Energeticsmentioning

confidence: 99%

Massive band gap variation in layered oxides through cation ordering

Balachandran

Rondinelli

2015

Nat Commun

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“…The work function is then the negative of the Fermi energy. 63,64 The molecular dynamics simulations were performed using a time step of 0.5 fs at a mean temperature of 300 K. No constraints on the positions of the metal atoms or the geometry of the water molecules were applied. Two different initial configurations corresponding the up and down structures were considered ͑for a description of these structures see Sec.…”

Section: Computational Detailsmentioning

confidence: 99%

Ab initio studies of a water layer at transition metal surfaces

Vassilev

Santen

Koper

2005

The Journal of Chemical Physics

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This paper presents a detailed study of a water adlayer adsorbed on Pt(111) and Rh(111) surfaces using periodic density functional theory methods. The interaction between the metal surface and the water molecules is assessed from molecular dynamics simulation data and single point electronic structure calculations of selected configurations. It is argued that the electron bands around the Fermi level of the metal substrate extend over the water adlayer. As a consequence in the presence of the water layer the surface as a whole still maintains its metallic conductivity—a result of a crucial importance for understanding the process of electron transfer through the water/metal interface and electrochemical reactions in particular. Our results also indicate that there exists a weak bond between the hydrogen of the water and the Rh metal atoms as opposed to the widespread (classical) models based on purely repulsive interaction. This suggests that the commonly used classical interactions potentials adopted for large scale molecular dynamics simulations of water/metal interfaces may need revision. Two adsorption models of water on transition metals with the OH bonds pointing towards or away of the surface are also examined. It is shown that due to the very close values of their adsorption energies one should consider the real structure of water on the surface as a mixture of these simple “up” and “down” models. A model for the structure of the adsorbed water layer on Rh(111) is proposed in terms of statistical averages from molecular dynamics simulations.

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“…These values compare well with other calculations 22,24 and the expected larger work function for the ͑111͒ surface is reproduced. The absolute values for the bare surface should be taken with some caution as no extensive testing of the dependence of the work function values on our model has been done ͑see the recent work of Fall et al 25 for a discussion on the determination of work functions from calculations͒.…”

Section: B Calculations For the Adsorption Of Ammonia On The "111… Amentioning

confidence: 99%

Adsorption of ammonia on the rhodium (111), (100), and stepped (100) surfaces: An ab initio and experimental study

Frechard

Santen

Siokou

et al. 1999

The Journal of Chemical Physics

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The adsorption of ammonia on the two low index ͑111͒ and ͑100͒ surfaces of rhodium has been studied by periodic calculations with density functional theory and compared to experimental results. The geometries of the adsorbates and the surfaces are completely optimized. For both surfaces the top site is found to be the most stable while the adsorption energy of ammonia is 8-10 kJ•mol Ϫ1 larger on the ͑100͒ surface. The presence of steps on the ͑100͒ surface has a minor effect on the heat of adsorption. The theoretical predictions of the adsorption energies and the changes in work function by NH 3 are in good agreement with experimental data. Moreover the prediction of the ontop adsorption as well as the weak interactions between the adsorbates is confirmed. The broadening of the temperature programmed desorption spectra and the two desorption peaks for the first adlayer are mainly due to an entropy effect which affects the preexponential factor of the desorption rate constant.

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Deriving accurate work functions from thin-slab calculations

Cited by 177 publications

References 26 publications

Massive band gap variation in layered oxides through cation ordering

Massive band gap variation in layered oxides through cation ordering

Ab initio studies of a water layer at transition metal surfaces

Adsorption of ammonia on the rhodium (111), (100), and stepped (100) surfaces: An ab initio and experimental study

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