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Recent studies have demonstrated that tellurene is a van der Waals (vdW) two-dimensional material with potential optoelectronic and thermoelectric applications as a result of its pseudo-one-dimensional structure and properties. Here, we report on the pressure induced anomalous phase transition of tellurium nanoribbons. The observation of clean phase transitions was made possible with high quality single crystalline Te nanoribbons that are synthesized by hydrothermal reaction growth. The results show that phase transition has a large pressure hysteresis and multiple competing phases: during compression, the phase transition is sudden and takes place from trigonal to orthorhombic phase at 6.5 GPa. Orthorhombic phase remains stable up to higher pressures (15 GPa). In contrast, phase transition is not sudden during decompression, but orthorhombic and trigonal phases co-exist between 6.9 to 3.4 GPa. Grüneisen parameter calculations further confirm the presence of co-existing phases and suggest hysteretic phase change behavior. Finally, orthorhombic to trigonal phase transition occurs at 3.4 GPa which means overall pressure hysteresis is around 3.1 GPa. 

Implicit solvent models divide solvation free energies into polar and nonpolar additive contributions, whereas polar and nonpolar interactions are inseparable and nonadditive. We present a feature functional theory (FFT) framework to break thisad hocdivision. The essential ideas of FFT are as follows: (i) representability assumption: there exists a microscopic feature vector that can uniquely characterize and distinguish one molecule from another; (ii) feature‐function relationship assumption: the macroscopic features, including solvation free energy, of a molecule is a functional of microscopic feature vectors; and (iii) similarity assumption: molecules with similar microscopic features have similar macroscopic properties, such as solvation free energies. Based on these assumptions, solvation free energy prediction is carried out in the following protocol. First, we construct a molecular microscopic feature vector that is efficient in characterizing the solvation process using quantum mechanics and Poisson–Boltzmann theory. Microscopic feature vectors are combined with macroscopic features, that is, physical observable, to form extended feature vectors. Additionally, we partition a solvation dataset into queries according to molecular compositions. Moreover, for each target molecule, we adopt a machine learning algorithm for its nearest neighbor search, based on the selected microscopic feature vectors. Finally, from the extended feature vectors of obtained nearest neighbors, we construct a functional of solvation free energy, which is employed to predict the solvation free energy of the target molecule. The proposed FFT model has been extensively validated via a large dataset of 668 molecules. The leave‐one‐out test gives an optimal root‐mean‐square error (RMSE) of 1.05 kcal/mol. FFT predictions of SAMPL0, SAMPL1, SAMPL2, SAMPL3, and SAMPL4 challenge sets deliver the RMSEs of 0.61, 1.86, 1.64, 0.86, and 1.14 kcal/mol, respectively. Using a test set of 94 molecules and its associated training set, the present approach was carefully compared with a classic solvation model based on weighted solvent accessible surface area. © 2017 Wiley Periodicals, Inc. 

Abstract Alloying selected layered transitional metal trichalcogenides (TMTCs) with unique chain‐like structures offers the opportunities for structural, optical, and electrical engineering thus expands the regime of this class of pseudo‐one‐dimensional materials. Here, the novel phase transition in anisotropic Nb_(1−x)Ti_xS₃alloys is demonstrated for the first time. Results show that Nb_(1−x)Ti_xS₃can be fully alloyed across the entire composition range from triclinic‐phase NbS₃to monoclinic‐phase TiS₃. Surprisingly, incorporation of a small concentration of Ti (x ≈0.05–0.18) into NbS₃host matrix is sufficient to induce triclinic to monoclinic transition. Theoretical studies suggest that Ti atoms effectively introduce hole doping, thus rapidly decreases the total energy of monoclinic phase and induces the phase transition. When alloyed, crystalline and optical anisotropy are largely preserved as evidenced by high resolution transmission electron microscopy and angle‐resolved Raman spectroscopy. Further Raman measurements identify Raman modes to determine crystalline anisotropy direction and offer insights into the degree of anisotropy. Overall results introduce Nb_(1−x)Ti_xS₃as a new and easy phase change material and mark the first phase engineering in anisotropic van der Waals (vdW) trichalcogenide systems for their potential applications in two‐dimensional superconductivity, electronics, photonics, and information technologies.