First-principles study of the adsorption and reaction of Se and SeO2 on O2/CaO(001) surface
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摘要: 基于密度泛函理论的第一性原理和平板模型构造了最稳定的O2/CaO(001)表面,通过优化Se和SeO2在此表面可能的初始吸附结构得到最佳吸附构型,分析了Se原子在O2/CaO(001)表面向SeO2的转化。结果表明,Se原子在O2/CaO(001)表面的稳定吸附构型主要有两种,即O-Se-O和O-O-Se基团,其中,O-O-Se基团的Se终端具有一定化学活性;Se在O2/CaO(001)表面向SeO2转化所需反应能垒小于均相条件下生成SeO2所需反应能垒,表明CaO不仅作为吸附剂,也能促进Se向SeO2的转化;SeO2分子在O2/CaO(001)表面发生化学吸附时,吸附基底的部分价电子转移至SeO2分子轨道中。
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关键词:
- 密度泛函理论 /
- 第一性原理 /
- CaO(001)表面 /
- 反应能垒
Abstract: O2/CaO(001) surface with the lowest energy was built by using the slab model and the first-principles method based on density functional theory. A series of possible adsorption configurations were optimized to get the adsorption geometries with the lowest energy for selenium (Se) and SeO2 on the O2/CaO(001) surface and the conversion of Se to SeO2 on the CaO(001) surface was then investigated. The results indicate that there are two adsorption configurations for Se atom on the O2/CaO(001) surface, viz., O-Se-O and O-O-Se groups; therein the Se terminal in O-O-Se group has a certain chemical activity. The reaction energy barrier for the heterogeneous conversion of Se and O2 to SeO2 is less than that for the homogeneous conversion, which means that CaO can not only act as an adsorbent, but also promote the conversion of Se to SeO2 as a catalyst; certain valence electrons in adsorption substrate are transferred to the orbits of SeO2 molecule when SeO2 molecule was adsorbed on the O2/CaO(001) surface.-
Key words:
- density functional theory /
- first-principles /
- CaO(001) surface /
- reaction energy barrier
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图 6 SeO2在O2/CaO(001)表面吸附前后Se、O(2)、Casurf原子态密度图(a)吸附前O(2)、Casurf原子态密度;(b)吸附后O(2)、Casurf原子态密度;(b)吸附后Se、O(2)原子态密度
Figure 6 DOS of Se, O(2) and Casurf before/after SeO2 adsorption on the O2/CaO(001) surface: (a): DOS of O(2) and Casurf before adsorption; (b): DOS of O(2) and Casurf after adsorption; (c): DOS of Se and O(2) after adsorption
表 1 O2在CaO(001)表面O2到CaO(001)表面平均距离、O(1)-O(2)键长、吸附能及电荷分析
Table 1 Equilibrium distance, optimized O(1)-O(2) bond length, adsorption energy, Mulliken charges after the adsorption of O2 on CaO(001) surface
Surface d/nm dO(1)-O(2)/nm q(O2)/e q(Osurf)/e q(Casurf)/e Ead/eV CaO(001) - 0.123 - -5.41 5.67 - O2/CaO(001) 0.271 0.130 -0.44 -4.88 5.28 -0.96 Mulliken charges - - -0.44 0.53 -0.39 - 表 2 Se在O2/CaO(001)表面的吸附能及Se原子Mulliken布居
Table 2 Adsorption energy and Mulliken population of Se on O2/CaO(001) surface
Number Adsorption configuration Ead/eV q(Se)/e a Se on bridge -1.31 0.20 b Se on O(1)-top -1.31 0.20 c Se on O(2)-top -2.47 0.18 表 3 SeO2在O2/CaO(001)表面的吸附能及电荷分析
Table 3 Adsorption energy and Mulliken population of SeO2 on O2/CaO(001) surface
Number Adsorption configuration Ead/eV q(Se to O)/e q(SeO2)/e a O(1)-top case 1, SeO2 is parallel to O2 -1.38 0.09 -0.36 b O(1)-top case 1, SeO2 is perpendicular to O2 -2.03 0.07 -0.55 c O(1)-top case 2, O atoms of SeO2 are deviated from O(2) -2.02 0.08 -0.54 d O(1)-top case 2, O atoms of SeO2 are toward O(2) -0.48 0.05 -0.18 e bridge case 1, SeO2 is parallel to O2 -2.02 0.09 -0.51 f bridge case 1, SeO2 is perpendicular to O2 -2.03 0.07 -0.56 g bridge case 2, O atoms of SeO2 are toward O(1) -2.02 0.09 -0.53 h bridge case 2, O atoms of SeO2 are toward O(2) -1.99 0.10 -0.49 i O(2)-top case 1, SeO2 is parallel to O2 -1.35 0.07 -0.40 j O(2)-top case 1, SeO2 is perpendicular to O2 -0.49 0.06 0.17 k O(2)-top case 2, O atoms of SeO2 are toward O(1) -1.90 0.07 -0.53 l O(2)-top case 2, O atoms of SeO2 are deviated from O(1) -2.02 0.07 -0.56 a: case 1 denotes that the SeO2 on O2/CaO (001) surface perpendicula;
b: case 2 denotes that the SeO2 on O2/CaO (001) surface parallel -
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