Hydrogen diffusion and trapping in α-iron: The role of quantum and anharmonic fluctuations

Cheng B, Paxton AT, Ceriotti M. 2018. Hydrogen diffusion and trapping in α-iron: The role of quantum and anharmonic fluctuations. Physical Review Letters. 120(22), 225901.


Journal Article | Published | English

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Author
Cheng, BingqingIST Austria ; Paxton, Anthony T.; Ceriotti, Michele
Abstract
We investigate the thermodynamics and kinetics of a hydrogen interstitial in magnetic α-iron, taking account of the quantum fluctuations of the proton as well as the anharmonicities of lattice vibrations and hydrogen hopping. We show that the diffusivity of hydrogen in the lattice of bcc iron deviates strongly from an Arrhenius behavior at and below room temperature. We compare a quantum transition state theory to explicit ring polymer molecular dynamics in the calculation of diffusivity. We then address the trapping of hydrogen by a vacancy as a prototype lattice defect. By a sequence of steps in a thought experiment, each involving a thermodynamic integration, we are able to separate out the binding free energy of a proton to a defect into harmonic and anharmonic, and classical and quantum contributions. We find that about 30% of a typical binding free energy of hydrogen to a lattice defect in iron is accounted for by finite temperature effects, and about half of these arise from quantum proton fluctuations. This has huge implications for the comparison between thermal desorption and permeation experiments and standard electronic structure theory. The implications are even greater for the interpretation of muon spin resonance experiments.
Publishing Year
Date Published
2018-06-01
Journal Title
Physical Review Letters
Volume
120
Issue
22
Article Number
225901
ISSN
eISSN
IST-REx-ID

Cite this

Cheng B, Paxton AT, Ceriotti M. Hydrogen diffusion and trapping in α-iron: The role of quantum and anharmonic fluctuations. Physical Review Letters. 2018;120(22). doi:10.1103/physrevlett.120.225901
Cheng, B., Paxton, A. T., & Ceriotti, M. (2018). Hydrogen diffusion and trapping in α-iron: The role of quantum and anharmonic fluctuations. Physical Review Letters. American Physical Society. https://doi.org/10.1103/physrevlett.120.225901
Cheng, Bingqing, Anthony T. Paxton, and Michele Ceriotti. “Hydrogen Diffusion and Trapping in α-Iron: The Role of Quantum and Anharmonic Fluctuations.” Physical Review Letters. American Physical Society, 2018. https://doi.org/10.1103/physrevlett.120.225901.
B. Cheng, A. T. Paxton, and M. Ceriotti, “Hydrogen diffusion and trapping in α-iron: The role of quantum and anharmonic fluctuations,” Physical Review Letters, vol. 120, no. 22. American Physical Society, 2018.
Cheng B, Paxton AT, Ceriotti M. 2018. Hydrogen diffusion and trapping in α-iron: The role of quantum and anharmonic fluctuations. Physical Review Letters. 120(22), 225901.
Cheng, Bingqing, et al. “Hydrogen Diffusion and Trapping in α-Iron: The Role of Quantum and Anharmonic Fluctuations.” Physical Review Letters, vol. 120, no. 22, 225901, American Physical Society, 2018, doi:10.1103/physrevlett.120.225901.
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PMID: 29906144
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arXiv 1803.00600

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