Carbon nanodots (CDots) are frequently adopted to modify composite photocatalysts, due to their unique optical properties and adjustable band structure. Here, an ab initio approach based on extend Hückel theory is used to study in detail the dependent relationship between the optical properties of carbon nanodots and surface relaxation. In order to imitate the surface structure of carbon nanodots, a number of two-layer tiny carbon domains are used. The energy level distribution shows a clear band gap, demonstrating the features of semiconductor. The band structure is somewhat bent as a result of surface relaxation's dramatic effect on the highest occupied molecular orbital (HOMO). The ultraviolet and visible absorption spectra of carbon nanodots are successfully predicted in theory, by considering the oscillator strength in every possibility transition, and the transition from the valence band maximum (VBM) to conduction band minimum (CBM) is the main peak location. The surface relaxation results in red shift of the spectral lines, which is the potential reason why carbon nanodots promote visible light absorption.

碳纳米点（CDots）由于其独特的光学性质和可调节的能带结构，经常被用来修饰复合光催化剂。在这里，基于扩展 Hückel 理论的从头算方法用于详细研究碳纳米点的光学性质与表面弛豫之间的依赖关系。为了模仿碳纳米点的表面结构，使用了许多两层微小的碳域。能级分布显示出明显的带隙，显示出半导体的特性。由于表面弛豫对最高占据分子轨道的显着影响，能带结构有些弯曲（同人）。通过考虑每一种可能跃迁中的振子强度，理论上成功地预测了碳纳米点的紫外和可见吸收光谱，并且从价带最大值（VBM）到导带最小值（CBM）的跃迁是主峰位置。表面弛豫导致谱线红移，这是碳纳米点促进可见光吸收的潜在原因。