First-principles density functional theory (DFT) electronic structure calculations were carried out for the model halogen-doped VO2 (M1 phase) to evaluate the effect of halogen (X = F, Cl, Br, I) doping on the band edges. The model structures of X-doped VO2 with X at V site or O site were constructed on the basis of 96-atom 2 × 2 × 2 supercell of monoclinic M1 phase of VO2. Our results showed that the band gap Eg2 for Cl-doped VO2 at O1 site (0.51 eV) is smaller than that of F-doped VO2 at O1 site (0.61 eV) and that of pure VO2 (0.78 eV). We also investigated the substitution of chlorine, bromine, and iodine for vanadium in VO2, where the band gaps Eg2 are 0.40, 0.45, and 0.37 eV for Cl-, Br-, and I-doped VO2 at V site, respectively. The Cl-doped VO2 at V site is the best one for achieving good VO2 thermochromic energy-saving foils.

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The mechanisms of iron­(II) bromide-catalyzed intramolecular C–H bond amination [1,2]-shift tandem reactions of aryl azides have been studied using density functional theory calculations. The tandem reaction from R 1 , 1-azido-2-(1-methoxy-2-methylpropan-2-yl)­benzene, to produce P 2 , 2,3-dimethyl-1H-indole, was calculated. Our results showed that the overall catalytic cycle includes the following steps: (I) extrusion of N2 to form iron nitrene; (II) C–H bond amination; (III) formation of the middle product P 1 , 2-methoxy-3,3-dimethylindoline; (IV) iminium ion formation ; (V) [1,2]-shift process; and (VI) formation of indole P 2 . The rate-limiting step is the [1,2]-shift process, where the energy barrier ΔE = 28.7 kcal/mol in the gas phase. Our calculated results also indicated that the preference for the [1,2]-shift component of the tandem reaction is methyl < ethyl.

First‐principles calculations based on density functional theory (DFT) are used to investigate the phase transition characteristics, electronic structures, and optical properties of pure and Co‐doped VO2 (M1 and R phase). Studies show that the metal‐to‐insulator phase transition temperature of VO2 is significantly reduced after Co doping, which is correlated to the decrease of bandgap value. Besides, the decrease of the energy required for electron transition of M1‐phase Co‐doped VO2 corresponds to the imaginary part of the dielectric peak moving to the low‐energy region. For both the M1‐ and R‐phase VO2, the visible light transmissivity of the Co‐doped VO2 is increased than that of pure VO2, which is beneficial to the application of VO2 film as visible windows. In addition, the absorptivity and reflectivity of Co‐doped R‐phase VO2 in the infrared light range are larger than those of M1‐phase VO2, indicating that the Co‐doped VO2 can block more infrared light at higher temperature to fulfill the purpose of lowering temperature. Overall, these results give new insights for the application of Co‐doped VO2 as a photoenergy material to regulate the room temperature.