Enabling QM-accurate simulation of dislocation motion in γ−Ni and α−Fe using a hybrid multiscale approach

Abstract

We present an extension of the 'learn on the fly' method to the study of the motion of dislocations in metallic systems, developed with the aim of producing information-efficient force models that can be systematically validated against reference QM calculations. Nye tensor analysis is used to dynamically track the quantum region centered at the core of a dislocation, thus enabling quantum mechanics/molecular mechanics simulations. The technique is used to study the motion of screw dislocations in Ni-Al systems, relevant to plastic deformation in Ni-based alloys, at a variety of temperature/strain conditions. These simulations reveal only a moderate spacing (∼5 Å) between Shockley partial dislocations, at variance with the predictions of traditional molecular dynamics (MD) simulation using interatomic potentials, which yields a much larger spacing in the high stress regime. The discrepancy can be rationalized in terms of the elastic properties of an hcp crystal, which influence the behavior of the stacking fault region between Shockley partial dislocations. The transferability of this technique to more challenging systems is addressed, focusing on the expected accuracy of such calculations. The bcc α-Fe phase is a prime example, as its magnetic properties at the open surfaces make it particularly challenging for embedding-based QM/MM techniques. Our tests reveal that high accuracy can still be obtained at the core of a dislocation, albeit at a significant computational cost for fully converged results. However, we find this cost can be reduced by using a machine learning approach to progressively reduce the rate of expensive QM calculations required during the dynamical simulations, as the size of the QM database increases.

Hybrid quantum/classical study of hydrogen-decorated screw dislocations in tungsten: Ultrafast pipe diffusion, core reconstruction, and effects on glide mechanism

“…The embedding region is then made large enough in order to accommodate far-field deformation. This latter technique, used here, is an example of a hybrid QM/MM simulation [29,30]. In all cluster methods, an additional layer of redundant "buffer" atoms is required in the ab initio cluster simulation to mitigate electronic effects induced by the artificial free surface of the cluster.…”

Atomistic QM/MM simulations of the strength of covalent interfaces in carbon nanotube–polymer composites

“…This method gave excellent agreement with the fully quantum calculations of the functional group detachment 46 at a fraction of computational cost. Similar QM/MM techniques have been used successfully to simulate crack propagation in silicon, 47,48 dislocation motion in metals 49 and molecular adsorption on a CNT surface. 50,51 In this work, we study how the chemical structure at the CNT-polymer interface determines its failure characteristics by simulating CNT pull-out from a cross-linked PE matrix.…”

Moment tensor potential for static and dynamic investigations of screw dislocations in bcc Nb

“…Very few data exist for the glide motion of screw dislocations in pure bcc metals using large supercells and MLIPs [31,34,79]. Both Wang et al [34], using an extended modified EAM potential for bcc V at 77 K, and Maresca et al [79], using a GAP potential for bcc Fe at 200 K, reported that the screw dislocation starts to glide on the (101) plane via double-kink nucleation and growth.…”

“…In the case of MTPs additionally, it is not possible (like, e.g. for Gaussian processes [31]) to calculate explicitly the correlation between different configurations in the set. The question of a proper training set is thus always central to the construction of an MLIP, as it will fail to provide accurate predictions for underrepresented atomic environments.…”