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Article

First-Principles Exploration of the Electronic Structure and Optical Properties of S-Doped Bi4O5Br2

by
Gaihui Liu
1,2,
Huihui Shi
1,2,
Nan Dong
2,
Xinrui Cao
2,
Xuan Gao
2,
Suqin Xue
1,* and
Fuchun Zhang
2,*
1
Network Information Center, Yan’an University, Yan’an 716000, China
2
School of Physics and Electronic Information, Yan’an University, Yan’an 716000, China
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(3), 228; https://doi.org/10.3390/catal15030228
Submission received: 28 November 2024 / Revised: 21 February 2025 / Accepted: 25 February 2025 / Published: 27 February 2025
(This article belongs to the Special Issue Cutting-Edge Photocatalysis)
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Versions Notes

Abstract

:
At present, many research studies have explored the modification of Bi4O5Br2, but relatively few have focused on non-metallic doping. In particular, the effect of S doping on its photocatalytic mechanism remains unclear. Hence, this study systematically investigates the modulation mechanism of the electronic structure and optical properties of Bi4O5Br2 by doped S using density functional theory (DFT) calculations. The calculated results indicate that the Br4Br1 model, in which S replaces Br at sites 4 and 1, is the most thermodynamically stable configuration. Comparing the models before and after doping, it is found that S doping significantly alters the lattice parameters of Bi4O5Br2, thus affecting its electronic structure. Furthermore, differential charge density calculations reveal that S doping improves the charge transfer capability and enhances the separation efficiency of photogenerated electron–hole pairs in Bi4O5Br2. Calculated absorption spectra demonstrate that S doping augments the light absorption of Bi4O5Br2 in the low- and medium-energy regions. Moreover, the dielectric function calculations further validate the effect of S doping on the optical properties of Bi4O5Br2. Specifically, there is an increase in polarization and energy loss in the low-energy region, with the opposite trend in the middle- and high-energy regions. Overall, S doping elevated the light absorption capacity and charge transfer efficiency of Bi4O5Br2 by altering its lattice parameter and electronic structure, which facilitated the enhancement of photocatalytic performance. This study provides new insights into the development of efficient photocatalytic materials and broadens the potential of Bi4O5Br2 for photocatalytic applications.

1. Introduction

With the rapid development of the global economy and intensification of industrialization, the problems of energy shortage and environmental pollution are becoming increasingly serious [1]. In particular, organic pollutants and bacteria in industrial wastewater seriously pollute the soil, air, and drinking water essential for human survival, and environmental pollution has become a common challenge faced by all countries worldwide [2,3,4]. Searching for environmentally friendly photocatalytic materials to replace non-renewable energy sources has become one of the effective strategies to solve current environmental pollution and energy crises. Photocatalytic technology is a high-efficiency, low-energy, low-cost, and non-secondary-pollution environmental treatment method and clean energy production technology. This technology utilizes semiconductor photocatalysts to generate active species under sunlight irradiation, which decompose pollutants into harmless water and carbon dioxide through redox reactions. Photocatalytic technology not only effectively addresses environmental problems but also makes full use of the inexhaustible solar energy resources, which has become one of the hot spots in the environmental remediation field [5,6].
Among many photocatalytic materials, bismuth-based semiconductors exhibit enormous application potential and advantages in photocatalysis due to their rich layered structure, tunable bandgap, excellent physicochemical stability, and high electron–hole mobility [7,8]. In particular, the special physical properties of bismuth oxide and the diversity of its crystal morphology mean it is widely used in sensors, optoelectronic materials, microelectronic components, and various types of catalysts [9,10,11]. In the study of bismuth-rich halide oxide materials, Bi4O5Br2 has attracted considerable attention owing to its unique crystal structure. Bi4O5Br2 consists of alternating layers of [Bi2O2]2⁺ lamellae and double bromine atoms [4,10], which enables more efficient separation of photogenerated electron–hole pairs in the presence of a polarization-induced electric field. In addition, Bi4O5Br2 is characterized by high chemical stability, a large specific surface area, strong light absorption capacity, and short diffusion distance, which lead to its excellent performance in photocatalysis [12,13,14]. However, the application of Bi4O5Br2 as a photocatalyst still faces several challenges. Firstly, Bi4O5Br2 has a limited visible light absorption range (<450 nm), which restricts its photocatalytic activity in the visible region. Secondly, the wide optical band gap (2.54 eV) of Bi4O5Br2 implies that only high-energy photons can excite electron–hole pairs, reducing the photocatalytic efficiency [15]. Meanwhile, Bi4O5Br2 lacks carrier-enriched sites, which hinders the further improvement of its photocatalytic performance [16].
To overcome these limitations, researchers have explored a variety of modification methods, including the construction of heterostructures [17,18], surface modification [19], elemental doping [20,21], and the preparation of composite photocatalysts [22]. Pd doping of Bi4O5Br2 has been proven to be an effective strategy to improve its catalytic performance [20]. The increase in catalytic activity is attributed to the formation of a Schottky barrier between Pd and Bi4O5Br2, which broadens the absorption range of Bi4O5Br2 in visible light and significantly improves the photocatalytic degradation of BPA. Zhang et al. [23] explored the photocatalytic activity of Bi4O5Br2 by doping Mn. The results of experiments and theoretical calculations indicated that the introduction of Mn did not change the surface morphology or physical phase of Bi4O5Br2. It was discovered that Mn doping reduces the band gap of Bi4O5Br2, extends the visible light absorption range, and improves the separation efficiency of electrons and holes. By constructing a TiO2/Bi4O5Br2 heterostructure, the light absorption ability of the catalyst was improved [24]. Meanwhile, the separation and migration of photogenerated carriers were facilitated, which significantly enhanced the photocatalytic performance. These research advances provide new ideas and methods for the application of modified Bi4O5Br2 in photocatalysis. Notably, non-metallic doping has extraordinary potential to augment the photocatalytic performance of Bi-based semiconductor materials.
BiOBr photocatalysts with flower-like microspherical morphologies have been successfully synthesized with an N/S doping strategy, which exhibited excellent activity and stability in the degradation of organic pollutants such as rhodamine B (RhB) and phenol [25]. F doping could modify the lattice parameter and energy band structure of Bi2MoO6, leading to a decrease in the band gap and a negative conduction band potential, which improved the photocatalytic efficiency [26]. Weng et al. [27] prepared CQDs/S-Bi4O5Br2 materials for the photocatalytic degradation of ciprofloxacin. The findings demonstrated that S-doped carbon quantum dots could augment the light absorption and photogenerated electron–hole pair separation efficiency of Bi4O5Br2. Furthermore, the doping site and concentration have a crucial influence on the photocatalytic performance of Bi-based materials [28,29,30]. Specifically, appropriate concentrations of non-metallic doping can optimize the energy band structure and surface chemistry of the material. Meanwhile, issues such as lattice distortion and an increased recombination rate of photogenerated carriers, which may result from a high doping concentration, can be avoided. Although previous studies have demonstrated the exciting potential of non-metallic doping for photocatalysis, the modification mechanism of Bi4O5Br2 by S doping remains unclear.
In this study, the modification of Bi4O5Br2 is realized by S doping. Based on DFT calculations, the effects of S doping on the energy band structure, density of states, differential charge, absorption spectra, and dielectric function of Bi4O5Br2 are thoroughly investigated. The intrinsic mechanism of S doping in modulating the photocatalytic performance of Bi4O5Br2 is revealed. This study provides theoretical evidence for the development of efficient photocatalytic materials.

2. Results and Discussion

2.1. Structural Modeling

In this work, all computational models are constructed based on the primitive crystal structure of Bi4O5Br2, as shown in Figure 1a, which contains 16 Bi atoms, 20 O atoms, and 8 Br atoms. Seven different S-doped Bi4O5Br2 (S-BOB) models are constructed by replacing Br at different sites and in different combinations [31], namely, Br1 (Figure 1b), Br2 (Figure 1c), Br3 (Figure 1d), Br4 (Figure 1e), Br4Br1 (Figure 1f), Br4Br2 (Figure 1g), and Br4Br3 (Figure 1h).

2.2. Structural Optimization

The base state energies of these seven models are obtained by structural optimization, and their formation energies are calculated by the following equation [32]:
ΔES = EX-BOB − EBOB + n EBr − n ES
where EX-BOB is the energy of S-BOB, EBOB is the energy of pure Bi4O5Br2, ES is the energy of S atoms, and EBr is the energy of Br atoms. As shown in Table 1, the Br4Br1 model has a minimum formation energy of 2.53 eV. Therefore, the Br4Br1 model (S-BOB) is chosen for property calculations and analyses in subsequent research. The electron numbers of per before and after doping are 416 and 414, respectively (Text S1).
Additionally, we performed spin-polarized calculations of the energy band structure and density of states (DOS) for S-doped Bi4O5Br2, considering both the substitution of one Br atom with one S atom and the substitution of two Br atoms with two S atoms (Figures S1 and S2). The results demonstrate that the inclusion of spin polarization has a negligible impact on the electronic structure, with the primary characteristics of the energy bands and DOS remaining unchanged. Therefore, spin polarization will be disregarded in the subsequent property calculations.
The lattice parameter a is increased from 10.89 Å to 10.92 Å after S doping compared to Bi4O5Br2 (Table 2). This indicates that S doping can lead to lattice expansion. Furthermore, the lattice angles α increase from 90° to 90.64°, β from 97.72° to 97.97°, and γ from 90° to 91.44°, which implies that the lattice symmetry and the internal stress state also change slightly. This is mainly attributed to the difference in radius and electronegativity between the S atom (r = 105 pm) and the Br atom (r = 114 pm). S doping with a smaller atomic radius and higher electronegativity leads to the tuning of the length and bond angles of the surrounding Bi-O bonds, thus causing lattice distortion. Accordingly, new or defect energy levels may be introduced to alter the energy band structure, which improves the separation and migration rate of photogenerated carriers [11,33]. Therefore, it is feasible to modulate the photocatalytic properties of Bi4O5Br2 by S doping.

2.3. Energy Band Structure and Density of States

In this study, the energy band structure of Bi4O5Br2 and S-BOB were calculated using the PBE functional. As shown in Figure 2a, the calculated band gap of pristine Bi4O5Br2 is 2.56 eV, which is close to the experimental value of 2.38 eV [34]. Additionally, we compared our results with the experimentally measured and theoretically predicted band gaps of Bi4O5Br2 reported in the literature (Table S1), further validating the reliability of our calculations. The band gap values obtained using the HSE06 functional were 3.57 eV for Bi4O5Br2 and 3.42 eV for S-BOB (Figure S3). The band gap of the S-BOB is obtained as 3.23 eV by considering both the HSE06 generalization and the spin–orbit coupling (Figure S4). These findings indicate that the PBE functional provides a band gap prediction more consistent with the experimental data. Therefore, subsequent property calculations were performed using the PBE functional.
The band structure analysis reveals that the valence band maximum (VBM) and conduction band minimum (CBM) of Bi4O5Br2 are located at different k-points in the Brillouin zone, indicating that Bi4O5Br2 is an indirect band gap semiconductor. The presence of an indirect band gap is beneficial for suppressing the recombination of photogenerated charge carriers, thereby enhancing photocatalytic activity [35]. Notably, after sulfur doping, the band gap of Bi4O5Br2 decreases to 2.43 eV (Figure 2b), which is consistent with previous reports where S doping reduced the band gap of BiOBr [36]. The reduction in the band gap allows S-BOB to absorb more visible light, which is crucial for improving its photocatalytic performance. Additionally, sulfur doping introduces impurity states within the band gap, facilitating the transition of electrons from the valence band to the conduction band and thereby enhancing the separation efficiency of photogenerated charge carriers [37]. Moreover, these impurity states promote faster charge carrier mobility, further improving the photocatalytic activity [38]. In summary, the modification of the electronic structure through sulfur doping significantly enhances the visible-light absorption capacity of S-BOB, leading to an improved photocatalytic performance.
The impact of S doping on the Bi4O5Br2 electronic structure is further elucidated by the density of states. As depicted in Figure 2c, the valence band top of pure Bi4O5Br2 consists mainly of hybridization of the Br 4p and O 2p orbitals, while the bottom of the conduction band is dominated by the Bi 6p and O 2s orbitals. This implies that Br and O play an important role in the distribution of electronic states. The density of states for S-BOB indicates that the S 3p state contributes remarkably to the top of the valence band apart from the Br 4p and O 2p states (Figure 2d). This involvement of the S 3p state demonstrates that S doping effectively alters the electronic structure of Bi4O5Br2. Moreover, the doped S 3p states provide additional electron transition pathways, facilitating electron transitions from the valence band to the conduction band. Furthermore, the local density of states variation introduced by S doping may also alter the surface activity of Bi4O5Br2 and increase the photocatalytic reaction rate. Changes in the electronic structure of Bi4O5Br2 cause a decrease in the band gap, which hinders the recombination probability of photogenerated electron–hole pairs. This is crucial for improving the photocatalytic performance of Bi4O5Br2, as more efficient carrier separation can accelerate the photocatalytic reaction.
To further investigate the impact of sulfur doping on the electronic structure of Bi4O5Br2, the spin–orbit coupling (SOC) effect was taken into account (Figure S5). The results show that, although the band gap slightly decreases from 2.43 eV to 2.25 eV when considering SOC, the orbital contributions near the Fermi level remain consistent. Specifically, the Bi orbitals continue to dominate near the band edges, and the inclusion of SOC does not significantly alter the key characteristics of the electronic properties. This indicates that, although SOC is an important relativistic effect in Bi-based materials, its influence on the electronic properties of Bi4O5Br2 is relatively minor. Therefore, SOC was not considered in subsequent property calculations.

2.4. Differential Charge Density

To further analyze the electronic structure and electron transfer process of S-BOB, the differential charge densities of pristine Bi4O5Br2 and S-BOB were calculated. As shown in Figure 3a, there is a clear charge accumulation around the O atoms in Bi4O5Br2, while the Bi atoms exhibit a charge deficit. This suggests that the electrons in pure Bi4O5Br2 are predominantly concentrated on the O atoms, while the Bi atoms tend to lose electrons due to their lower electronegativity. Furthermore, the absence of significant charge redistribution around the Br atoms demonstrates that there is relatively little charge involvement of the Br atoms in pure Bi4O5Br2, which may be attributed to the stability of the Bi4O5Br2 electronic structure.
Figure 3b presents the differential charge density distribution of S-BOB. A clear yellow area can be observed around the S atoms, which indicates a strong charge accumulation phenomenon. Meanwhile, the charge densities around the O and Bi atoms are reduced compared to pure Bi4O5Br2, implying that S doping significantly affects the charge redistribution. The introduction of S atoms alters the localized electronic structure, enhancing electron–atom interactions and facilitating charge transfer and separation. This charge redistribution is related to the van der Waals interactions generated by S doping. In brief, S atoms attract more electrons through their higher electronegativity, which improves the charge transfer efficiency of Bi4O5Br2. Furthermore, S doping improves the charge transfer path due to charge redistribution and also boosts the separation efficiency of electrons and holes. Meanwhile, the introduction of S atoms results in a significant electron accumulation on the surface of the system, which has a positive effect on the catalytic activity [31]. The redistribution of charge density optimizes the electronic structure of Bi4O5Br2, confirming the positive role of S doping in enhancing the optoelectronic properties of Bi4O5Br2.

2.5. Electron Localization Function

Figure 4 exhibits the two-dimensional distribution of the electron localization function (ELF) for Bi4O5Br2 and S-BOB. As shown in Figure 4a, the electron localization regions (red areas) in Bi4O5Br2 are relatively limited, with most ELF values concentrated in the higher range (green to blue areas). This indicates a low degree of electron localization in the intrinsic Bi4O5Br2, with electrons tending to delocalize. This results in a higher tendency for electron–hole pairs recombination, limiting the photocatalytic activity of Bi4O5Br2.
In comparison, S-BOB exhibits stronger electron localization, particularly in specific regions with prominent red highly localized areas, as illustrated in Figure 4b. This demonstrates that S doping introduces new electronic states or redistributes electrons, leading to increased localization in certain regions. The enhanced localization can suppress the recombination electron–hole pairs. Furthermore, the ELF in S-BOB is more uniformly distributed in high-value regions, highlighting the significant role of S atoms in modulating the electronic structure of Bi4O5Br2. This uniform electron localization may improve charge separation efficiency and carrier migration of S-BOB.
In summary, S doping significantly modulates the electronic localization properties of Bi4O5Br2. The enhanced electronic localization and optimized distribution may contribute to improving the photocatalytic performance of S-BOB.

2.6. Absorption Spectrum

To investigate the influence of S doping on the light absorption properties of Bi4O5Br2, the absorption spectra were calculated. As illustrated in Figure 5, the absorption intensity of S-BOB is slightly higher than that of pure Bi4O5Br2 in the low-energy region (<4 eV). This result indicates that S doping improves the light absorption capacity of Bi4O5Br2 in this energy range. This may be attributed to the introduction of a new electronic state in the S 3p orbital, inducing an increase in photon absorption [27,39]. Notably, the absorption of low-energy photons contributes to the efficient utilization of Bi4O5Br2 in the visible region.
In the middle-energy region (6–9 eV), the absorption intensity of S-BOB is slightly higher than that of pure Bi4O5Br2. Remarkably, a distinct characteristic absorption peak near 7 eV can be observed. This absorption peak is attributed to the electron transition from the top of the valence band to the bottom of the conduction band involving the O 2p and Bi 6p orbitals. It can be concluded that S doping both tunes the electronic band structure and increases the probability of electron transitions, thus promoting the photogenerated carrier generation and separation efficiency.
In the high-energy region (>10 eV), the absorption intensity of S-BOB is lower than that of pure Bi4O5Br2, suggesting a minor effect of S doping in this energy region. This may be due to the fact that in the high-energy region, the electron transitions are mainly dependent on the intrinsic electronic structure of Bi4O5Br2 rather than on S doping.
To conclude, by altering the Bi4O5Br2 electronic structure, S doping significantly improves its light absorption in the low- and medium-energy ranges. Moreover, S doping causes the absorption peaks to be blue-shifted and extended into the low-energy region, with less effect on the high-energy region. Furthermore, the new electronic states introduced by S doping augment the generation and separation efficiency of electron–hole pairs.

2.7. Dielectric Function

The dielectric function reflects the electromagnetic response characteristics of catalysts at different energies. Therefore, the dielectric functions of Bi4O5Br2 and S-BOB are calculated to investigate the modulation mechanism of S doping on the optical properties of Bi4O5Br2. The equations for the real and imaginary parts of the dielectric function are provided in the Supplementary Materials (Equations (S1)–(S3)).
ϵ(ω) = ϵ 1(ω) + i ϵ 2 (ω)
where ϵ1(ω) denotes the real part of the dielectric function, ϵ2(ω) denotes the imaginary part of the dielectric function, and ω is the frequency of light.
The real part of the dielectric function is determined by the polarization response of catalysts, including electronic and ionic polarization. Meanwhile, the imaginary part of the dielectric function is mainly related to the light absorption and energy loss of catalysts. As displayed in Figure 6a, the real parts of the Bi4O5Br2 and S-BOB dielectric functions exhibit similar trends in the energy range from 0 to 8 eV. Nevertheless, the real part of the S-BOB dielectric function is slightly higher than that of Bi4O5Br2 in the low-energy interval (0–3.1 eV). This finding reveals that the polarizability of Bi4O5Br2 in the low-energy interval is enhanced by S doping. This may be attributed to the impurity energy levels introduced by S doping, which increases the electron density and electron–hole pair polarization of the S-BOB. Moreover, a distinct peak occurs in the energy range of 3.1–5 eV for Bi4O5Br2, whereas the corresponding peak for S-BOB is slightly lower. This suggests that S doping weakens the response of Bi4O5Br2 to polarization in this energy interval and reduces the opportunity for electron transitions.
As shown in Figure 6b, the imaginary part of the S-BOB dielectric function is slightly higher than that of Bi4O5Br2 in the low-energy interval (0–4 eV). This indicates that S doping aggravates the energy loss of Bi4O5Br2 in this energy interval, which can be explained by the fact that S doping introduces additional absorption centers, promoting the absorption efficiency of Bi4O5Br2. In the middle- to high-energy interval (4–6 eV), the imaginary part of the Bi4O5Br2 dielectric function exhibits a pronounced peak, with a slightly lower corresponding peak for S-BOB. This observation implies that S doping moderates the energy loss of Bi4O5Br2 in this energy interval, thus diminishing its absorption of photon energy. The above results show that S doping primarily optimizes the polarization response of Bi4O5Br2 in the low-energy region and accelerates its energy loss.

3. Calculation Details

In this study, all calculations were performed using Device Studio-integrated Projector Augmented-Wave (DS-PAW) package in the Device Studio program (2024A) [40], and the cutoff energy for the plane-wave expansion was set to 450 eV. The convergence criteria for the energy and force were set to 1 × 10−5 eV and 0.01 eV/Å, respectively. The first Brillouin zone was sampled using a 3 × 6 × 3 k-point grid. The exchange-correlation interactions were described using the Perdew–Burke–Ernzerhof (PBE) functional within the generalized gradient approximation (GGA) [11,41,42,43]. The calculation precision was set to “Accurate”.

4. Conclusions

In this work, we systematically examined the modulation mechanism of S doping on the electronic structure and optical properties of Bi4O5Br2 photocatalysts. The Br4Br1 model had the lowest formation energy and the most stable thermodynamic properties according to density functional theory (DFT) calculations. Energy band and density of states calculations revealed that S doping reduces the band gap of Bi4O5Br2 (2.43 eV) and dramatically alters its electronic structure. The differential charge density analysis indicated that the charge around S atoms in S-BOB is clustered, while on the contrary, the charge density of O and Bi atoms is reduced. This suggests that S doping has led to an improvement in the charge transfer efficiency and the separation rate of photogenerated electron–hole pairs. Absorption spectrum calculations illustrated that S doping significantly augments the light absorption of Bi4O5Br2 in the low- and medium-energy regions, especially exhibiting a characteristic absorption peak at around 7.0 eV. This is attributed to the new electronic states introduced by S doping and the enhanced electron–hole pair separation efficiency. The light absorption in the high-energy region is less affected, indicating that S doping mainly improves the photocatalytic performance of Bi4O5Br2 in the visible region. Calculations of the dielectric function further verify the effect of S doping on the optical properties. Specifically, S doping enhances the polarization of Bi4O5Br2 in the low-energy region, while attenuating its polarization response in the middle- and high-energy regions. Overall, S doping can significantly improve the optical absorption and charge transfer efficiency of Bi4O5Br2 by modifying its lattice parameters and electronic structure. This work offers new ideas for designing non-metal-doped Bi4O5Br2 and expands the potential of Bi4O5Br2 for photocatalytic applications.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/catal15030228/s1, Figure S1: Spin-polarized energy band structure and DOS of S-doped Bi₄O₅Br₂ with one Br atoms replaced by one S atoms; Figure S2: Spin-polarized energy band structure and DOS of S-doped Bi₄O₅Br₂ with two Br atoms replaced by two S atoms; Figure S3: Energy band structures of (a) Bi₄O₅Br₂ and (b) S-BOB using the HSE06 functional; Figure S4: (a) Energy band structure and (b) density of states of S-BOB considering both HSE06 functions and SOC; Figure S5: (a) Energy band structure and (b) density of states of S-BOB considering spin-orbit coupling (SOC); Table S1: Comparison of experimental and theoretical band gaps of Bi₄O5Br₂; Texts 1: Changes in the number of electrons before and after doping; Texts 2: Formulae related to the real and imaginary parts of the dielectric function [44,45,46,47,48,49,50].

Author Contributions

Conceptualization, F.Z.; formal analysis, X.G.; methodology, G.L.; project administration, S.X.; resources, G.L. and X.C.; visualization, H.S. and N.D.; writing—original draft, G.L.; writing—review and editing, G.L. and F.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (No. 62264015), and Suqin Xue was partially supported by the postgraduate research opportunities program of HZWTECH (HZWTECH-PROP).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within this article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 15 00228 g001
Figure 1. Models of (a) Bi4O5Br2 and (b–h) seven structures of S doped BOB.
Figure 1. Models of (a) Bi4O5Br2 and (b–h) seven structures of S doped BOB.
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Figure 2. Energy band structures of (a) Bi4O5Br2 and (b) S-BOB; density of states of (c) Bi4O5Br2 and (d) S-BOB. The Fermi energy level is set to 0.
Figure 2. Energy band structures of (a) Bi4O5Br2 and (b) S-BOB; density of states of (c) Bi4O5Br2 and (d) S-BOB. The Fermi energy level is set to 0.
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Figure 3. Differential charge densities of (a) Bi4O5Br2 and (b) S-BOB (Yellow is positive, blue is negative).
Figure 3. Differential charge densities of (a) Bi4O5Br2 and (b) S-BOB (Yellow is positive, blue is negative).
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Figure 4. Electron localization function of (a) Bi4O5Br2 and (b) S-BOB.
Figure 4. Electron localization function of (a) Bi4O5Br2 and (b) S-BOB.
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Figure 5. Absorption spectra of Bi4O5Br2 and SBOB.
Figure 5. Absorption spectra of Bi4O5Br2 and SBOB.
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Figure 6. Dielectric functions of Bi4O5Br2 and S-BOB: (a) real parts and (b) imaginary parts.
Figure 6. Dielectric functions of Bi4O5Br2 and S-BOB: (a) real parts and (b) imaginary parts.
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Table 1. Formation energies of seven different S-BOB models.
Table 1. Formation energies of seven different S-BOB models.
ConfigurationBr1Br2Br3Br4Br4Br1Br4Br2Br4Br3
Energy (eV)2.722.732.742.622.532.983.23
Table 2. Lattice parameters of Bi4O5Br2 and S-BOB.
Table 2. Lattice parameters of Bi4O5Br2 and S-BOB.
Speciesa (Å)b (Å)c (Å)α (°)β (°)γ (°)
Bi4O5Br210.895.6714.609097.7290
S-BOB10.925.6714.5890.6497.9791.44
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Liu, G.; Shi, H.; Dong, N.; Cao, X.; Gao, X.; Xue, S.; Zhang, F. First-Principles Exploration of the Electronic Structure and Optical Properties of S-Doped Bi4O5Br2. Catalysts 2025, 15, 228. https://doi.org/10.3390/catal15030228

AMA Style

Liu G, Shi H, Dong N, Cao X, Gao X, Xue S, Zhang F. First-Principles Exploration of the Electronic Structure and Optical Properties of S-Doped Bi4O5Br2. Catalysts. 2025; 15(3):228. https://doi.org/10.3390/catal15030228

Chicago/Turabian Style

Liu, Gaihui, Huihui Shi, Nan Dong, Xinrui Cao, Xuan Gao, Suqin Xue, and Fuchun Zhang. 2025. "First-Principles Exploration of the Electronic Structure and Optical Properties of S-Doped Bi4O5Br2" Catalysts 15, no. 3: 228. https://doi.org/10.3390/catal15030228

APA Style

Liu, G., Shi, H., Dong, N., Cao, X., Gao, X., Xue, S., & Zhang, F. (2025). First-Principles Exploration of the Electronic Structure and Optical Properties of S-Doped Bi4O5Br2. Catalysts, 15(3), 228. https://doi.org/10.3390/catal15030228

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