Quantum Theory of Diffusion with Application to Light Interstitials in Metals

Flynn, C. P.; Stoneham, A. M.

doi:10.1103/physrevb.1.3966

Cited by 682 publications

(225 citation statements)

References 16 publications

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“…At very low temperatures, coherent tunneling is expected to be the dominant mechanism, giving way to phonon-assisted tunneling as the temperature increases, and eventually to classical over-barrier jumps at still higher temperatures. 17 Hirth 1 suggests that at temperatures above 300 K diffusion could be described by small polaron theory, 62 whereas at temperatures above 800 K, H diffuses in a partly delocalized manner. In this work, which represents our first attempt at integrating diffusion kinetics with mechanics, we ignore these myriad complications and simply describe diffusion by over-barrier hops in the temperature range 300-600 K.…”

Section: B Kmc Model For Diffusionmentioning

confidence: 99%

Effect of atomic scale plasticity on hydrogen diffusion in iron: Quantum mechanically informed and on-the-fly kinetic Monte Carlo simulations

et al. 2008

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We present an off-lattice, on-the-fly kinetic Monte Carlo (KMC) model for simulating stress-assisted diffusion and trapping of hydrogen by crystalline defects in iron. Given an embedded atom (EAM) potential as input, energy barriers for diffusion are ascertained on the fly from the local environments of H atoms. To reduce computational cost, on-the-fly calculations are supplemented with precomputed strain-dependent energy barriers in defect-free parts of the crystal. These precomputed barriers, obtained with high-accuracy density functional theory calculations, are used to ascertain the veracity of the EAM barriers and correct them when necessary. Examples of bulk diffusion in crystals containing a screw dipole and vacancies are presented. Effective diffusivities obtained from KMC simulations are found to be in good agreement with theory. Our model provides an avenue for simulating the interaction of hydrogen with cracks, dislocations, grain boundaries, and other lattice defects, over extended time scales, albeit at atomistic length scales.

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Section: B Kmc Model For Diffusionmentioning

confidence: 99%

Effect of atomic scale plasticity on hydrogen diffusion in iron: Quantum mechanically informed and on-the-fly kinetic Monte Carlo simulations

et al. 2008

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“…49 The Debye temperature for beryllium is quite high and so the quantum corrections can be neglected only above ϳ200°C, which, however, can be relevant e.g. for the operation of beryllium components of fusion reactors.…”

Section: A Hydrogen Atoms In Interstitial Positionsmentioning

confidence: 99%

Hydrogen in beryllium: Solubility, transport, and trapping

2009

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The paper presents the results of ab initio simulation of hydrogen properties in beryllium. Both interstitial hydrogen positions in the lattice and various hydrogen positions in a vacancy have been studied. The most energetically favorable interstitial hydrogen configuration among the four considered high-symmetry configurations is the basal tetrahedral one, in agreement with the earlier predictions. The most probable diffusion pathway for hydrogen atoms in the bulk involves the exchange of octahedral and basal tetrahedral positions with the effective migration energy of ϳ0.4 eV. For hydrogen atom in a vacancy, an off-center ͑nearly basal tetrahedral͒ configuration is definitely preferred. Addition of more hydrogen atoms to a vacancy remains energetically favorable up to at least five hydrogen atoms, though the binding energies fall down with the increase in the number of hydrogen atoms in the vacancy.

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“…Now, if the potential wells for a H atom in two neighboring sites are not the same, one expects that the vibrational states can no longer line up, and the quantum tunneling will be reduced [40]. With an effective energy difference " between two vibrational ground states at the two neighboring adsorption sites, the tunneling diffusion rate assisted by phonons can be approximated by [41] …”

Section: Prl 97 166101 (2006) P H Y S I C a L R E V I E W L E T T E mentioning

confidence: 99%

Quantum Diffusion of H on Pt(111): Step Effects

2006

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Using a linear optical diffraction technique, we have systematically investigated the defect effects on quantum surface diffusion of hydrogen on Pt(111) surfaces. The quantum tunneling effect was clearly observed for hydrogen diffusion at low temperatures as manifested by a leveling off of the diffusion coefficient on flat surfaces. The strong influence of surface defects on the quantum diffusion is in good agreement with the creation of an inhomogeneous surface with adsorption sites of different binding energies. DOI: 10.1103/PhysRevLett.97.166101 PACS numbers: 68.35.Fx, 68.35.Dv, 68.43.Jk, 82.20.Xr Because of the small mass of the hydrogen atom and the weakly corrugated potential energy surface, diffusion of hydrogen on metal surfaces may take both classical overbarrier hopping and quantum mechanical under-barrier tunneling. Quantum effects in surface diffusion are of broad interest and have been intensively studied both experimentally [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and theoretically [16 -26]. The first observation of a nearly temperature independent surface (chemical) diffusivity of H on W(110) in the low temperature regime by Gomer and coworkers [1] using field emission microscopy (FEM) has stimulated a great theoretical effort [16 -26] because of the observed unexpected different behavior from the light atom diffusion in bulk metals, for which a much stronger temperature dependence was found [27]. Experimentally, while similar behaviors were observed by the same group using the same technique for H on a number of other metal surfaces [2 -7], only one report using a different technique, scanning tunneling microscopy (STM), has confirmed the weak temperature dependence of surface (tracer) diffusivity for H on Cu(100) [13], but at a diffusion rate about 6 -9 orders of magnitude slower (10 ÿ19 cm 2 = sec vs 10 ÿ10 -10 ÿ13 cm 2 = sec). Using a linear optical diffraction (LOD) technique that probes diffusion over a length scale of microns, Zhu and his coworkers found an activated quantum diffusion with a strong temperature dependence for H on Ni(111) [11,12] and Ni(100) [8], drastically different from what has been observed by Gomer and his coworkers on the same systems [7]. These differing and apparently contradictory observations, using different techniques, need to be resolved in order to remove any doubts on the experimental observation of quantum surface diffusion.Recognizing that different techniques detect different physical properties of a system, and that such properties might be influenced by different processes, we studied the quantum effects in surface diffusion using one of the above techniques, the linear optical diffraction technique [28][29][30]. The system we have chosen is H on Pt(111), because there is a theoretical prediction for this system [26], and we have extensively studied the over-barrier diffusion of this system [31]. Compared to FEM and STM, which detect the H diffusion only within a single well-ordered terrace, the linear optical diffraction technique probes...

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Quantum Theory of Diffusion with Application to Light Interstitials in Metals

Cited by 682 publications

References 16 publications

Effect of atomic scale plasticity on hydrogen diffusion in iron: Quantum mechanically informed and on-the-fly kinetic Monte Carlo simulations

Effect of atomic scale plasticity on hydrogen diffusion in iron: Quantum mechanically informed and on-the-fly kinetic Monte Carlo simulations

Hydrogen in beryllium: Solubility, transport, and trapping

Quantum Diffusion of H on Pt(111): Step Effects

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