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Molecular engineering plays a critical role in the development of electron donor and acceptor materials for improving power conversion efficiency (PCE) of organic photovoltaics (OPVs). The halogenated acceptor materials in OPVs have shown high PCE. Here, to investigate the halogenation mechanism and the effects on OPV performances, based on the density functional theory calculations with the optimally tuned screened range-separated hybrid functional and the consideration of solid polarization effects, we addressed the halogenation effects of acceptor ITIC, which were modeled by bis-substituted ITIC with halogen and coded as IT-2X (X = F, Cl, Br), and PBDB-T:ITIC, PBDB-T:IT-2X (X = F, Cl, Br) complexes on their geometries, electronic structures, excitations, electrostatic potentials, and the rate constants of charge transfer, exciton dissociation (ED), and charge recombination processes at the heterojunction interface. The results indicated that halogenation of ITIC slightly affects molecular geometric structures, energy levels, optical absorption spectra, exciton binding energies, and excitation properties. However, the halogenation of ITIC significantly enlarges the electrostatic potential difference between the electron acceptor and donor PBDB-T with the order from fluorination and chlorination to bromination. The halogenation also increases the transferred charges of CT states for the complexes. Meanwhile, the halogenation effects on CT energies and electron process rates depend on different haloid elements. No matter which kinds of haloid elements were introduced in the halogenation of acceptors, the ED is always efficient in these OPV devices. This work provides an understanding of the halogenation mechanism, and is also conducive to the designing of novel materials with the aid of the halogenation strategy.

Accelerated soil erosion is an undesirable process that adversely affects the conservation of water and soil. This paper used a procedure linking the Revised Universal Soil Loss Equation (RUSLE) and geographic information system (GIS) to map the soil erosion level from 1990 to 2010 caused by land-cover change in the Dongjiang River basin, China. Results indicate that the significant land-cover change greatly impacted soil erosion. The overall soil erosion level of the basin belonged to Level II (mild erosion) but the erosion amount shown an uptrend. Erosion areas of Levels I and II occupied more than 90% and other levels (Levels III–VI) occupied less than 10% of the total area. Approximately 90.85% of the area maintained the original levels, 5.84% converted from lower levels to higher levels, and 3.32% converted from higher levels to lower levels. The erosion in the downstream regions was more serious than that in the central and upstream regions. Although soil erosion was mild as a whole in the study region, some local areas underwent intense erosion. The study demonstrated that linking RUSLE with GIS tools is an efficient procedure for mapping soil erosion levels at basin scale. The gradual deterioration condition caused by land-cover changes at present or in the future requires further study.

Rainfall-induced landslide susceptibility assessment is currently considered an effective tool for landslide hazard assessment as well as for appropriate warning and forecasting. As part of the assessment procedure, a credible index weight matrix can strongly increase the rationality of the assessment result. This study proposed a novel weight-determining method by using random forests (RFs) to find a suitable weight. Random forest weights (RFWs) and eight indexes were used to construct an assessment model of the Dongjiang River basin based on fuzzy comprehensive evaluation. The results show that RF identified the elevation (EL) and slope angle (SL) as the two most important indexes, and soil erodibility factor (SEF) and shear resistance capacity (SRC) as the two least important indexes. The assessment accuracy of RFW can be as high as 79.71%, which is higher than the entropy weight (EW) of 63.77%. Two experiments were conducted by respectively removing the most dominant and the weakest indexes to examine the rationality and feasibility of RFW; both precision validation and contrastive analysis indicated the assessment results of RFW to be reasonable and satisfactory. The initial application of RF for weight determination shows significant potential and the use of RFW is therefore recommended.