Understanding Chemical Bonding in Alloys and the Representation in Atomistic Simulations

Abstract

Alloys are widely used in catalysts and structural materials. The nature of chemical bonding and the origin of alloy formation energies, defect energies, and interfacial properties have not been well understood to date but are critical to material performance. In this contribution, we explain the polar nature of chemical bonding and an implementation in classical and reactive atomistic simulations to understand such properties more quantitatively. Electronegativity differences between metal atoms lead to polar bonding, and exothermic alloy formation energies are related to charge transfer between the different elements. These differences can be quantified by atomic charges using pairwise charge increments, determined by matching the computed alloy formation energy to experimentally measured alloy formation energies using pair potentials for the pure metals. The polar character of alloys is comparable to organic molecules and partially ionic minerals, for example, AlNi and AlNi3 alloys assume significant atomic charges of ±0.40e and +0.60e/–0.20e, respectively. The subsequent analysis of defect sites and defect energies using force-field-based calculations shows excellent agreement with calculations using density functional theory and embedded atom models (EAM). The formation of vacancy and antisite defects is characterized by a redistribution of charge in the first shell of neighbor atoms in the classical models whereby electroneutrality is maintained and charge increments correlate with differences in electronegativity. The proposed atomic charges represent internal dipole and multipole moments, consistent with existing definitions for organic and inorganic compounds and with the extended Born model (Heinz, H.; Suter, U. W. J. Phys. Chem. B 2004, 108 (47), 18341–18352). The method can be applied to any alloy and has a reproducibility of ±10%. In contrast, quantum mechanical charge schemes remain associated with deviations exceeding ±100%. The atomic charges for alloys provide a simple initial measure for the internal electronic structure, surface adsorption of molecules, and reactivity in catalysis and corrosion. The models are compatible with the Interface force field (IFF), CHARMM, AMBER, OPLS-AA, PCFF, CVFF, and GROMOS for reliable atomistic simulations of alloys and their interfaces with minerals and electrolytes from the nanometer scale to the micrometer scale.

Accurate simulation of surfaces and interfaces of ten FCC metals and steel using Lennard–Jones potentials

“…1j) 30 , and properties of alloys (Supplementary Fig. 1k) 31 . The models can be extended to bcc metal structures and incorporate polarization by external electric fields on the fly using extensions with virtual electrons (Supplementary Fig.…”

Interpretable molecular models for molybdenum disulfide and insight into selective peptide recognition

“…36 We assign the atomic charges using the extended Born model, which captures the nature of chemical bonding and reproduces interfacial properties with solvents and other inorganic compounds and organic molecules. 36,38 Prior studies include no rationale for the atomic charges chosen and rely on ad-hoc assumptions from DFT calculations, which vary from one density functional or from partition method to another by several 100%. These approaches cannot consistently describe internal polarity using point-based charges.…”

“…These approaches cannot consistently describe internal polarity using point-based charges. 36,38,76,77 We further utilized equilibrium bond lengths and bond angles from reproducible X-ray data. Minor adjustments within few percent were permitted to account for small superimposed contributions by the nonbond interactions (last two terms in eqn (1) and 2).…”

“…Parameters that are consistently derived and explained, rather than numerically tted, achieve multiple times increased reliability and compatibility as shown by the interface force eld (IFF) and its surface model database. [35][36][37][38] In this study, we introduce parameters for MoS 2 with record accuracy (Fig. 1) including validation and application to explain specic binding of peptides and amino acid residues.…”

Plastic and low-cost zero thermal expansion alloy by a natural dual-phase composite

“…High-resolution TEM reveals a ~ 1 nm thick disordered transition layer at the interfaces as shown in 5c and 5d), respectively, implying that there exist some extent of semi-coherent lattice matching between the two phases. The transition layers connect H and α phases via chemical bonding, minimalizing interfacial energy and giving rise to strong interface linkage and excellent thermal stability 43,44 . Our thermal circulation test shows that the dual-phase ZTE alloys remain perfect integrity after hundreds of rapid switching between 77 K and 335 K (see Fig.…”