Grain boundaries (GBs) significantly affect the properties of materials. In an effort to examine the phenomena at GBs, many model boundaries, typically symmetric tilt GBs, have been investigated. However, the geometries of symmetric tilt GBs are too restricted to represent commonly occurring interface phenomena properly in polycrystalline materials. Thus, a method of applying density functional theory (DFT) to asymmetric GBs has long been desired. Here, we present a simple geometric method and a new GB model with two surfaces which make it possible to characterize an asymmetric tilt GB and calculate the GB energetics. Our method can be extended to study other geometric asymmetric interfaces in various materials. The proposed technique thus paves the way for DFT-related studies of asymmetric interfaces.

Fine particles (PM_2.5) were collected during all four seasons, from April 2001 to February 2002, in Seoul, South Korea, using an annular denuder system. Elemental compositions of ambient PM_2.5 were analyzed using the proton-induced X-ray emission method. The greatest contributors (≥2%) to the PM_2.5 mass were sulfur (S), silicon (Si), chlorine (Cl), aluminum (Al), and iron (Fe) in the spring; S in the summer; and S and Cl in the fall. S, Cl, and Si were the major elements in the winter. S was the most abundant species among the elements, ranging from 5.3 to 7.9%, followed by Si and Cl. From analysis of variance, PM_2.5 mass, Al, Si, potassium, calcium, and Fe showed significant seasonal differences during the four seasons (p < 0.001). Enrichment factor (EF) analysis was carried out to identify the sources affecting the aerosol in the Seoul area. On the basis of the mean EF values, elemental S, copper, zinc, and lead may be emitted from anthropogenic sources (EF > 50). Elemental Al, Si, titanium, and Fe may be emitted from crustal sources (EF < 3). Additionally, a correlation analysis was carried out for source identification. The results of the correlation analysis were confirmed by the results of the EF analysis.