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Quantum effects on dislocation motion from ring-polymer molecular dynamics

npj Computational Materials 2018年第1期4卷 198-203页

作者： Rodrigo Freitas Mark Asta vasily v.bulatov Department of Materials Science and Engineering University of CaliforniaBerkeleyCA 94720USA Lawrence Livermore National Laboratory LivermoreCA 94550USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA Department of Materials Science and Engineering Stanford UniversityStanfordCA 94305USA

Quantum motion of atoms known as zero-point vibration was recently proposed to explain a long-standing discrepancy between theoretically computed and experimentally measured low-temperature plastic strength of iron and possibly other metals with high atomic *** finding challenges the traditional notion that quantum motion of atoms is relatively unimportant in solids comprised of heavy *** we report quantum dynamic simulations of quantum effects on dislocation motion within the exact formalism of Ring-Polymer Molecular Dynamics(RPMD).To extend the reach of quantum atomistic simulations to length and time scales relevant for extended defects in materials,we implemented RPMD in the open-source code LAMMPS thus making the RPMD method widely available to the *** use our RPMD/LAMMPS approach for direct calculations of dislocation mobility and its effects on the yield strength ofα-*** simulation results establish that quantum effects are noticeable at temperatures below 50 K but account for only a modest(≈13% at T=0 K)overall reduction in the Peierls barrier,at variance with the factor of two reduction predicted earlier based on the more approximate framework of harmonic transition state *** results confirm that zero-point vibrations provide ample additional agitation for atomic motion that increases with decreasing temperature,however its enhancing effect on dislocation mobility is largely offset by an increase in the effective atom size,an effect known as quantum dispersion that has not been accounted for in the previous calculations.

关键词： theory quantum motion

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