Coupled quantum mechanics/molecular mechanics modeling of metallic materials: Theory and applications
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Coupled quantum mechanics/molecular mechanics modeling of metallic materials: Theory and applications Xu Zhang and Gang Lua) Department of Physics and Astronomy, California State University Northridge, Northridge, California 91330-8268, USA (Received 6 October 2017; accepted 9 January 2018)
We review two recent advances in coupled quantum mechanics/molecular mechanics (QM/MM) modeling for metallic materials. The QM/MM methods are formulated based on quantum mechanical charge density embedding. In the first method, QM/MM coupling is accomplished by an embedding potential evaluated via orbital-free density functional theory. The charge density embedding in the second QM/MM method is achieved through constrained density functional theory. The extension of QM/MM coupling to the quasicontinuum method is illustrated, offering a route toward quantum mechanical simulations of materials at micron scales and beyond. The theoretical formulations of the QM/MM methods are discussed in detail. We also provide some examples where the QM/MM methods have been applied to understand fundamental physics in a wide range of material problems, ranging from void formation, pipe diffusion along dislocation core, nanoindentation of thin films, hydrogen-assisted cracking, magnetism-induced plasticity to stress-controlled catalysis in metals. An outlook to future development of QM/MM methods for metals is envisioned.
I. INTRODUCTION
Despite ever increasing computational powers, modeling and simulation of complex materials at the atomic level—the subject of this Focus Issue—still remains a formidable challenge.1 On the one hand, quantum mechanics (QM) is indispensable for a proper treatment of bond-breaking, charge transfer, electron excitation, magnetism, etc., in materials. However, QM calculations are often so expensive that no more than a few hundred atoms can be handled routinely. On the other hand, atomistic simulations based on empirical interatomic potentials, termed molecular mechanical (MM) methods, are capable of describing small-amplitude vibrations and torsions, elastic deformation, electrostatic interactions, etc., in many material problems; these empirical MM methods can treat millions or more atoms in routine calculations. The coupled quantum mechanics/molecular mechanics (QM/MM) methods by combining the accuracy of the QM description with the low computational cost of MM modeling can thus offer a promising solution to the computational challenge in atomistic simulations of materials. In recent years, significant progress has been made in the development of QM/MM methodologies and the application of these methods in atomistic simulations of materials.2–23 There are generally two categories of Contributing Editor: Steven D. Kenny a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.15
QM/MM methods applicable to two different classes of materials. In materials where covalent bonds are dominant (organic and inorganic semiconductors, molecular materials, etc.), one can partition the system b
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