Work function calculation for thick metal slabs with local pseudopotentials

Reinaudi, Luis; Pópolo, Mario Del; Leiva, E.P.M.

doi:10.1016/s0039-6028(96)01254-x

Cited by 9 publications

(3 citation statements)

References 18 publications

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“…Besides, an added feature in our device is a metal/n-type semiconductor Ohmic junction established at the interface between Zn and ZnO nanotips. This is because the Fermi level of Zn (−4.2 eV) , is higher than that of ZnO (−4.4 eV, average value reported as the Fermi level for ZnO). – To achieve thermal equilibrium in this junction, electrons must flow from the Zn metal into the lower-energy states of the conduction band in the n-type semiconductor, that is, ZnO, which makes the ZnO in the junction region more n-type . As a consequence, we believe that the Fermi level of the entire ZnO nanotip is raised because the length of our ZnO nanotips is so short that a considerable section of the wire is affected by the electron accumulation layer.…”

Section: Resultsmentioning

confidence: 99%

Enhanced Electron Transport in Dye-Sensitized Solar Cells Using Short ZnO Nanotips on A Rough Metal Anode

Yang

Ito

et al. 2009

J. Phys. Chem. C

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Many efforts have been directed toward the enhancement of electron transport in dye-sensitized solar cells (DSSC) using one-dimensional nanoarchitectured semiconductors. However, the improvement resulting from these ordered 1-D nanostructured electrodes is often offset or diminished by the deterioration in other device parameters intrinsically associated with the use of these 1-D nanostrucutres, such as the two-sided effect of the length of the nanowires impacting the series resistance and roughness factor. In this work, we mitigate this problem by allocating part of the roughness factor to the collecting anode instead of imparting all the roughness factors onto the semiconductor layer attached to the anode. A microscopically rough Zn microtip array is used as an electron-collecting anode on which ZnO nanotips are grown to serve as the semiconductor component of the DSSC. For the same surface roughness factor, our Zn-microtip|ZnO-nanotip DSSC exhibits an enhanced fill factor compared with DSSCs that have ZnO nanowires supported by a planar anode. In addition, the open-circuit voltage of the Zn-microtip|ZnO-nanotip DSSC is also improved due to a favorable band shift at the Zn−ZnO interface, which raises the Fermi level of the semiconductor and consequently enlarges the energy gap between the quasi-Fermi level of ZnO and the redox species. With these improvements, the overall efficiency becomes 1.4% with an open-circuit voltage of 770 mV, while the surface roughness factor of ZnO is approximately 60. Electrochemical impedance spectroscopic study reveals that the electron collection time is much shorter than the electron lifetime, suggesting that fast electron collection occurs in our device due to the significantly reduced electron collection distance along the short ZnO nanotips. The overall improvement demonstrates a new approach to enhance the efficiency of dye-sensitized solar cells.

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Section: Resultsmentioning

confidence: 99%

Enhanced Electron Transport in Dye-Sensitized Solar Cells Using Short ZnO Nanotips on A Rough Metal Anode

Yang

Ito

et al. 2009

J. Phys. Chem. C

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“…[14][15][16] The electronic structure, instead, has been determined by means of angle-resolved photoemission experiments, 17 while ultraviolet photoemission spectroscopy has been used for accurate estimates of the Pt͑111͒ work function. 18 After the pioneering works of Lang and Kohn, [19][20][21][22][23] accurate calculations of Pt bulk and ͑111͒ surface [24][25][26][27][28][29][30][31][32][33][34] played an important role in the prediction of the behavior of the solid metal for technical applications. Stateof-the-art computational studies of bulk Pt and Pt surfaces 24,25 are based on density functional theory ͑DFT͒, 35 within the independent particle formalism of Kohn and Sham, 36 and employ the general gradient approximation ͑GGA͒ for the exchange-correlation functionals.…”

Section: Introductionmentioning

confidence: 99%

Modeling bulk and surface Pt using the “Gaussian and plane wave” density functional theory formalism: Validation and comparison to k-point plane wave calculations

Santarossa¹,

Vargas²,

Iannuzzi³

et al. 2008

The Journal of Chemical Physics

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We present a study on structural and electronic properties of bulk platinum and the two surfaces (111) and (100) comparing the Gaussian and plane wave method to standard plane wave schemes, normally employed for density functional theory calculations on metallic systems. The aim of this investigation is the assessment of methods based on the expansion of the Kohn-Sham orbitals into localized basis sets and on the supercell approach, in the description of the metallicity of Pt. Electronic structure calculations performed at Gamma-point only on supercells of different sizes, from 108 up to 864 atoms, are compared to the results obtained for the unit cell of four Pt atoms where the k-point expansion of the wave function over Monkhorst-Pack grids up to (10x10x10) has been employed. The evaluation of the two approaches with respect to bulk properties is done through the calculation of the equilibrium lattice constant, the bulk modulus, and the total and the d-projected density of states. For the Pt(111) and Pt(100) surfaces, we consider the relaxation of the first layers, the surface energies, the work function, the total density of states, as well as the center and filling of the d bands. Our results confirm that the accuracy of two approaches in the description of electronic and structural properties of Pt is equivalent, providing that consistent supercells and k-point meshes are used. Moreover, we estimate the supercell size that can be safely adopted in the Gaussian and plane wave method in order to obtain the same reliability of previous theoretical studies based on well converged plane wave calculations available in literature. The latter studies, in turn, set the level of agreement with experimental data. In particular, we obtain excellent agreement in the evaluation of the density of states for either bulk and surface systems, and our data are also in good agreement with previous works on Pt reported in literature. We conclude that Gaussian and plane wave calculations, with simulation cells of 400-800 atoms, can be safely used in the study of chemistry related problems involving transition metal surfaces. We present a study on structural and electronic properties of bulk platinum and the two surfaces ͑111͒ and ͑100͒ comparing the Gaussian and plane wave method to standard plane wave schemes, normally employed for density functional theory calculations on metallic systems. The aim of this investigation is the assessment of methods based on the expansion of the Kohn-Sham orbitals into localized basis sets and on the supercell approach, in the description of the metallicity of Pt. Electronic structure calculations performed at ⌫-point only on supercells of different sizes, from 108 up to 864 atoms, are compared to the results obtained for the unit cell of four Pt atoms where the k-point expansion of the wave function over Monkhorst-Pack grids up to ͑10ϫ 10ϫ 10͒ has been employed. The evaluation of the two approaches with respect to bulk properties is done through the calculation of the equilibrium latt...

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“…Work functions are commonly evaluated using this expression, by measuring the Fermi energy E s F of thin slabs with respect to the potential in the vacuum region [5][6][7][8][19][20][21][22]. In figure 1, we show the calculated local density of states (LDOS) of a six-layer-thick Al(100) slab.…”

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confidence: 99%

Deriving accurate work functions from thin-slab calculations

Fall

Binggeli

Baldereschi

1999

J. Phys.: Condens. Matter

177

159

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Quantum-size effects have been shown to influence significantly the determination of work functions from thin-slab calculations. We show here that a technique based on macroscopic averages can be used to reduce such effects and determine more precisely the work functions of metals from ab initio thin-film calculations. The technique combines the mean electrostatic potential step across the slab surface with the Fermi energy of a bulk crystal. The method is applied to Al(100) slabs containing 1-14 atomic layers.

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Work function calculation for thick metal slabs with local pseudopotentials

Cited by 9 publications

References 18 publications

Enhanced Electron Transport in Dye-Sensitized Solar Cells Using Short ZnO Nanotips on A Rough Metal Anode

Enhanced Electron Transport in Dye-Sensitized Solar Cells Using Short ZnO Nanotips on A Rough Metal Anode

Modeling bulk and surface Pt using the “Gaussian and plane wave” density functional theory formalism: Validation and comparison to k-point plane wave calculations

Deriving accurate work functions from thin-slab calculations

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