Recent Advances in Point Defect Studies Driven by Density Functional Theory

Abstract

We highlight some of the most salient recent advances in point defects studies obtained from atomic-scale simulations performed in the framework of the density functional theory. The refinement of the theory, combined with its efficient numerical implementations and the (until now) everlasting growth of computer power allowed the transition from qualitative (in the beginning of the 90’) to quantitative results. Some of the longstanding controversies in the field have been tackled, and as far as aluminum is concerned, it has been shown that the curvature in the Arrheniusplot is due to anharmonic effects rather than to a two-defect diffusion mechanism. The anomalous diffusion in the b (bcc) phase of the group-IV elements has been related to the strong structural relaxation around vacancies, which significantly reduces their formation energy. Self-interstitials have been studied in materials of technological interest, their structure and mobility have been analyzed allowing a better interpretation of experimental results and an improved understanding of processes occurring under irradiation. Dilute interstitial solid solutions have been investigated. The strong binding between C and vacancies in bcc Fe may partially explain the observed influence of low amounts of C on Fe self-diffusion; the attraction of H to stacking faults in a Zr should favor planar dislocations glide. Intermetallics involving Fe (Fe-Al, Fe-Co) behave like highly correlated systems requiring methodological improvements of the DFT for a quantitative description. However, valuable trends concerning the structural point defects (those that allow nonstoichiometric compositions at low temperature) as well as the temperature dependence of point defects concentrations have been obtained.

Chemomechanics of complex materials: challenges and opportunities in predictive kinetic timescales

“…Silica is a naturally occurring material, comprising silicate tetrahedra (SiO 4 ) in the crystalline form of quartz; it is the most abundant material in the Earth's crust and the key component of fiberoptic and dielectric-thin-film communication platforms. It is well known that water reduces the strength of silica through several mechanisms, including hydrolytic weakening of quartz due to interstitial water [24][25][26] and stress corrosion cracking of amorphous silica due to surface water [17,[19][20][21]. This interaction is representative of a broader class of chemomechanical degradation of material strength, including stress corrosion and hydrogen embrittlement in metals, and enzymatic biomolecular reactions.…”

“…The energy landscape of such Fe crystals is thus relatively smooth, notwithstanding the magnetic spin state of the atoms, and the activation barriers for nucleation of vacancies within the lattice can be determined directly via density functional theory (DFT) [3,[17][18][19][20][21]. The diffusion of single vacancies within the lattice must overcome an activation barrier, but in this case the energetic barrier of the diffusive unit process-atomic hopping to adjacent lattice sites-is defined by transition pathways that are essentially limited to < 100 > and < 111 > crystallographic directions.…”