Concerted Use of Slab and Cluster Models in an ab Initio Study of Hydrogen Desorption from the Si(100) Surface

Steckel, Janice A.; Phung, Truc; Jordan, Kenneth D.; Nachtigall, Petr

doi:10.1021/jp0035176

Cited by 42 publications

(42 citation statements)

References 70 publications

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“…B3LYP represents a significant improvement upon PW91, giving energies which are much closer to our QMC results, and only lower by about 0.05, 0.2, and 0.15 eV for Si 21 H 20 . This is in accordance with earlier studies using the B3LYP functional for the Si-H system [11,18,24]. Inter-dimer H2 and H4 mechanisms.…”

supporting

confidence: 93%

“…We optimized all geometries using the PW91 functional [17], which gives a good description of the structural properties of Si (lattice constant error < 1%). Moreover, for cluster models of H 2 /Si(001), the geometries optimized using PW91 and the hybrid functional B3LYP were found to be very similar [18], and the energetics of the reaction on both sets of geometries essentially the same within B3LYP (as shown below, B3LYP gives energies very close to our accurate QMC results). It is therefore a sound procedure to use QMC on geometries obtained from PW91 calculations to assess whether a more accurate treatment of electronic correlation can change the physical picture.…”

supporting

confidence: 66%

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Quantum Monte Carlo Calculations ofH2Dissociation on Si(001)

et al. 2002

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We present quantum Monte Carlo calculations for various reaction pathways of H2 with Si(001), using large model clusters of the surface. We obtain reaction energies and energy barriers noticeably higher than those from approximate exchange-correlation functionals. In improvement over previous studies, our adsorption barriers closely agree with experimental data. For desorption, the calculations give barriers for conventional pathways in excess of the presently accepted experimental value, and pinpoint the role of coverage effects and desorption from steps.The dissociative adsorption of molecular hydrogen on the Si(001) surface has become a paradigm in the study of adsorption systems. Despite its apparent simplicity, more than a decade of extensive experimental and theoretical investigations have not clarified fundamental aspects of the chemical reaction of H 2 with this surface.Many of the experimental observations are hard to reconcile in a unified picture: the sticking probability for dissociative adsorption of H 2 on the clean surface is very small at room temperature suggesting a high adsorption barrier; sticking increases dramatically with higher surface temperatures [1]. On the other hand, the nearly thermally distributed kinetic energy of desorbing molecules has lead researchers to the conclusion that the molecules have transversed almost no adsorption barrier [2]. Microscopically, these observations were originally interpreted in terms of an intra-dimer mechanism, where the hydrogen molecule interacts with one single dimer of the Si(001) surface [3]. However, very recent experiments have pointed to additional mechanisms involving not just a single dimer but nearby dimers [4,5]. The existence of highly reactive pathways was first demonstrated on steps [6] or H-precovered surfaces [7], and evidence that H 2 reacts with two adjacent dimers has also now been given for the clean surface [8]. In Fig. 1, the intra-dimer (H2*) and two inter-dimer pathways at different coverages (H2 and H4) are schematically shown.Theoretically, density-functional theory (DFT) calculations performed on intra-dimer and inter-dimer mechanisms have lead to limited agreement with experiments. While correctly predicting the existence of a barrier-less H4 inter-dimer reaction path at high coverages [9], previous DFT slab calculations yielded an adsorption barrier for the low-coverage H2* and H2 pathways too low to explain the small sticking coefficient observed at low temperatures [7]. Desorption barriers from DFT obtained within the generalized gradient approximation (GGA) were also generally lower than the experimental value (2.5 eV, Ref.[10]). Additional evidence for a possible inadequacy of DFT-GGA to describe this reaction comes from comparison with highly correlated quantum chemistry calculations for small cluster models of the surface: For the intra-dimer pathway, these methods obtain values for the desorption barrier that are at large variance with the DFT-GGA value [11][12][13]. In this Letter, we use quantum Monte Carlo (QMC)...

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supporting

confidence: 93%

supporting

confidence: 66%

Quantum Monte Carlo Calculations ofH2Dissociation on Si(001)

et al. 2002

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“…[13][14][15][16][17] The first uncertainty in these calculations is the validity of the surface model, which is either a hydrogen-terminated cluster or a periodic slab model containing several layers. 23 The simplest cluster model for Si͑100͒ is Si 9 H 12 , which has a single surface dimer. One can then increase the number of dimers systematically by adding more dimer units along the same row ͑Fig.…”

Section: Introductionmentioning

confidence: 99%

Are both symmetric and buckled dimers on Si(100) minima? Density functional and multireference perturbation theory calculations

Jung

Shao

Gordon

et al. 2003

The Journal of Chemical Physics

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We report a spin-unrestricted density functional theory(DFT) solution at the symmetric dimer structure for cluster models of Si(100). With this solution, it is shown that the symmetric structure is a minimum on the DFTpotential energy surface, although higher in energy than the buckled structure. In restricted DFT calculations the symmetric structure is a saddle point connecting the two buckled minima. To further assess the effects of electron correlation on the relative energies of symmetric versus buckled dimers on Si(100), multireference second order perturbation theory (MRMP2) calculations are performed on these DFT optimized minima. The symmetric structure is predicted to be lower in energy than the buckled structure via MRMP2, while the reverse order is found by DFT. The implications for recent experimental interpretations are discussed. KeywordsDensity functional theory, Perturbation theory, Electron correlation calculations, Potential energy surfaces Disciplines Chemistry CommentsThe following article appeared in Journal of Chemical Physics 119 (2003) We report a spin-unrestricted density functional theory ͑DFT͒ solution at the symmetric dimer structure for cluster models of Si͑100͒. With this solution, it is shown that the symmetric structure is a minimum on the DFT potential energy surface, although higher in energy than the buckled structure. In restricted DFT calculations the symmetric structure is a saddle point connecting the two buckled minima. To further assess the effects of electron correlation on the relative energies of symmetric versus buckled dimers on Si͑100͒, multireference second order perturbation theory ͑MRMP2͒ calculations are performed on these DFT optimized minima. The symmetric structure is predicted to be lower in energy than the buckled structure via MRMP2, while the reverse order is found by DFT. The implications for recent experimental interpretations are discussed.

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“…[11][12][13] There has been considerable theoretical effort to understand these processes. 14,15 Thermal and nonthermal, photon driven removal of H has been shown to result in quite different surfaces. 16 Direct single photon desorption of H from Si surfaces in UHV has been reported with 157 nm (7.9 eV) photons.…”

Section: Introductionmentioning

confidence: 99%

Photoreactivity of Si(111)−H in Ambient

Bodlaki

Borguet

2006

J. Phys. Chem. C

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Second harmonic generation rotational anisotropy (SHG-RA) provides a convenient means to monitor the chemical state of the Si surfaces and to follow the conversion of a H-terminated surface to SiO 2 by oxidation as a function of time in ambient. SHG at 800 nm is sensitive to changes in the surface electronic properties induced by oxidation, and it probes both the initial stage of oxidation and the logarithmic oxide growth. We found that intense, ultrashort (4 ps) 800 nm laser pulses accelerate the initial stage of oxidation of Si( 111)-H in ambient. The cross-section of the photoinduced process was found to be (1.7 ( 0.5) × 10 -23 cm 2 . A mechanism involving drift of photoexcited electrons toward the surface is proposed to explain the photooxidation.

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Concerted Use of Slab and Cluster Models in an ab Initio Study of Hydrogen Desorption from the Si(100) Surface

Cited by 42 publications

References 70 publications

Quantum Monte Carlo Calculations ofH2Dissociation on Si(001)

Quantum Monte Carlo Calculations ofH2Dissociation on Si(001)

Are both symmetric and buckled dimers on Si(100) minima? Density functional and multireference perturbation theory calculations

Photoreactivity of Si(111)−H in Ambient

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