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Based on density functional theory (DFT), the effects of scandium (Sc) doping and oxygen vacancy ([V.sub.O]) on the electronic states and optical properties of monoclinic BiV[O.sub.4] (m-BiV[O.sub.4]) are investigated. The generalized gradient approximation plus U (GGA+U) method is adopted during the calculation of the electronic properties to compensate for the limitations of the DFT method. The ideal m-BiV[O.sub.4] has a direct band gap of 2.400 eV, and if Bi in m-BiV[O.sub.4] is substituted by Sc ([sub.sub.Sc-Bi]), the direct band gap will be reduced to 2.393 eV. However, if V is replaced by Sc ([sub.sub.Sc-V]) as well as oxygen vacancy induced ([sub.sub.Sc-V]+[V.sub.O]), the band gap will become indirect with values of 1.913 and 2.198 eV, respectively. The reduction capability is in the sequence of [sub.sub.Sc-Bi] > ideal > [sub.sub.Sc-V]+[V.sub.O] > [sub.sub.Sc-V], while the oxidation capability is in the order of ideal > [sub.sub.Sc-Bi] > [sub.sub.Sc-V]+[V.sub.O] > [sub.sub.Sc-V]. The [[epsilon].sub.1](0) of the ideal, [sub.sub.Sc-Bi], [sub.sub.Sc-V], and [sub.sub.Sc-V]+[V.sub.O] defective m- BiV[O.sub.4] are 8.290, 8.293,12.791, and 8.285, respectively. The optical absorptions of ideal and [sub.sub.Sc-Bi] m-BiV[O.sub.4] show anisotropy and they are nearly independent of the defect concentration. [sub.sub.Sc-V] m-BiV[O.sub.4] exhibits stronger absorption than the other three semiconductors. The absorptions of [sub.sub.Sc-V]+[V.sub.O] m-BiV[O.sub.4] vary widely with the defect concentrations, where 3.906% defect concentration of m-BiV[O.sub.4] has the strongest absorption. The estimated optical band gaps [E.sup.opt.sub.g] are smaller than [E.sub.g] for ideal and defective m-BiV[O.sub.4]. Key words: doping, vacancy, electronic states, optical properties, m-BiV[O.sub.4]. Sur la base de la theorie de la fonctionnelle de densite (DFT), nous examinons les effets du dopage au scandium (Sc) et des lacunes en oxygene ([V.sub.O]) sur les etats electroniques et les proprietes optiques du compose monoclinique BiV[O.sub.4] (m-BiV[O.sub.4]). L'approche GGA+U est adoptee dans le calcul des proprietes electroniques afin de compenser les limitations de la methode TFD. Le m-BiV[O.sub.4] ideal a un gap direct de 2,400 eV et si le Bi est remplace par un Sc, ([sub.sub.Sc-Bi]), le gap direct est reduit a 2,393 eV. Cependant, si le V est remplace par un Sc ([sub.sub.Sc-V]), aussi bien qu'avec lacune en oxygene ([sub.sub.Sc-V]+[V.sub.O]), alors le gap devient indirect avec des valeurs de 1,913 eV et 2,198 eV respectivement. La capacite de reduction suit la sequence suivante, [sub.sub.Sc-Bi] > ideal > [sub.sub.Sc-V]+[V.sub.O] > [sub.sub.Sc-V], pendant que la capacite oxydante suit la sequence suivante, ideal > [sub.sub.Sc-Bi] > [sub.sub.Sc-V]+[V.sub.O] > [sub.sub.Sc-V]. La valeur de [[epsilon].sub.1](0) pour chacun des cas suivants, ideal, [sub.sub.Sc-Bi], [sub.sub.Sc-V] et [sub.sub.Sc-V]+[V.sub.O], est calculee etre 8,290, 8,293,12,791 et 8,285 respectivement. L'absorptions optique des cas ideal et [sub.sub.Sc-Bi] m-BiV[O.sub.4] montre une anisotropie et est pratiquement independantes des concentrations de defauts. [sub.sub.Sc-V] mBiV[O.sub.4] montre une plus forte absorption que les trois autres semi-conducteurs. Les absorptions de [sub.sub.Sc-V]+[V.sub.O] mBiV[O.sub.4] varient evidemment avec la concentration de defauts, la plus forte absorption se presentant a 3,906% de concentration de defauts de mBiV[O.sub.4]. Les gaps optiques estimes [E.sup.opt.sub.g] sont plus petits que [E.sub.g] pour tous les cas de m-BiV[O.sub.4], ideal et avec defauts. [Traduit par la Redaction] Mots-cles : dopage, lacune, etats electroniques, proprietes optiques, mBiV[O.sub.4]., 1. Introduction Due to the urgent issues of environmental pollution and energy shortage, many efforts have been done to explore the materials for solar energy conversion and organic pollutant degradation [...]

In this work, the structural, electronic and optical performances of PC6/MoSe2 heterostructure are investigated using first principles calculations based on density functional theory. The PC6/MoSe2 heterostructure displays type-I band alignment with a direct band gap of 0.84 eV, and its CBM and VBM are contributed by PC6. The heterojunction can be transformed from type-I to type-II under biaxial strain, even from semiconductor to metal in the presence of a strong strain within the range of elastic response. Meanwhile, the transition from type-I to type-II can be also observed when an electric field greater than 0.3 V/Å is applied. So the electronic properties of the PC6/MoSe2 heterostructure can be effectively modulated by applying biaxial strain and external electric field, which provides great potential for designing multifunctional devices. In addition, the optical absorption spectrum reveals that the PC6/MoSe2 heterostructure could present a good optical utilization performance, indicating that it may play an important role in the application of optoelectronic devices. The results suggest that the PC6/MoSe2 heterostructure can be widely used in optoelectronic, photocatalytic and light-emitting applications in future research. [ABSTRACT FROM AUTHOR]

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The photocatalytic properties of BiOI {001} monolayer are studied through density functional theory computations. The first-principle calculation results indicate that the structural stability of BiOI {001} monolayer under tensile strain is better than that under compressive strain. The band gap is decreasing gradually from compressive strain to tensile strain. Due to its smaller electron effective mass and the larger probability of carriers located in VBM and CBM, the electron transition ability of monolayer is also improved under tensile strain. In addition, the photoabsorption edges will give rise to a redshift for BiOI {001} monolayer under tensile strain, indicating that the utilization of visible-light region is broadened; thus, the photocatalytic performance is improved. So combined with its better structural stability and the better photoelectric properties, we prefer to apply appropriate tensile strain to BiOI {001} monolayer to improve its photocatalytic performance for practical applications. [ABSTRACT FROM AUTHOR]