Development of orthogonal tight-binding models for Ti-C and Ti-N systems

Abstract

We develop p-d orthogonal tight-binding (OTB) models for the description of TiCx and TiNx compounds in the 1.0>x>0.5 composition range. For the parametrization of bond integrals we use a recently developed method allowing projection of the one-electron wave functions obtained within the density functional theory onto optimized atom-centered orbitals. The performance of the OTB models is investigated for a wide range of properties: binding energy of elements and compounds, density of states, formation energy of vacancy-ordered defects, elastic constants, and phonon dispersions. The models provide a good description of the ground state properties at 1:1 composition and show a fair transferability for various atomic environments in elemental and binary phases

Self-assembly of Carbon Vacancies in Sub-stoichiometric ZrC1−x

“…Besides, the orbital-wise pCOHP analysis indicates that Zr-C bond is dominated by the p-d σ and π bonding with significant share of C( p z ) and Zr interactions. These bonding characters are consistent with other transition metal carbides like TiC 26 33 .…”

Competition between crystal-field, overlap, and three-center contributions inHNeigenspectra

“…Figure 5 shows the behavior of the bond integrals β n as a function of the distance that is predicted by Eq. (13). As expected from the definition of β ij in Eq.…”

“…However, as the modeling of materials becomes ever more sophisticated, the TB approaches have been faced with the challenge of how best to obtain a robust set of parameters that is fully transferable from one structure type or environment to the next. Following the pioneering ideas of the screened linear muffin-tin orbital method [9] in 1984 and the density-functional tight-binding method [10] in 1998, good progress has recently been made in deriving TB parameters directly from DFT using local-orbital projection methods [11][12][13][14]. These local orbitals may be overlapped in the presence of the fully self-consistent DFT potential to obtain the nonorthogonal tight-binding (NOTB) Hamiltonian matrix H in addition to the overlap matrix S. Finally, by using the standard Löwdin orthogonalization procedure [15], the orthogonal tight-binding (OTB) Hamiltonian matrixH may be found directly.…”

Understanding and mitigating hydrogen embrittlement of steels: a review of experimental, modelling and design progress from atomistic to continuum

“…Possible resolutions include: (1) improved interatomic potentials, e.g. coarse-grained from electronic structure in the bond order potential formulation [126] or automatically constructed using machine learning (ML) from a database of reference quantum mechanical (QM) configurations [10,15], (2) concurrent multiscale approaches where localised regions are modelled with QM precision within a non-uniform precision embedding scheme [17] enabling direct simulation of complex crack tip chemistry [97].…”