Graphitic carbon nitride (g-C₃N₄) has garnered much attention due to its potential as an efficient metal-free photocatalyst. This study examines the evolution of properties in zero-dimensional quantum dots up to sizable clusters that mimic extended g-C₃N₄ monolayers. We employ density functional theory to investigate systematically the structural, electronic, and optical properties of the g-C₃N₄-based melamine and heptazine building blocks using a “bottom-up” construction of polymeric monolayers. The results from our computations indicate that the melamine- and heptazine-based polymeric g-C₃N₄ systems must be reduced to at least 2.74 and 4.00 nm, respectively, to observe an increase of its optical gap with a size reduction. The present study also examines the nature of the electronic transitions exhibited by g-C₃N₄-based monolayers through full natural transition orbital and density of state analyses. The most promising sites for water splitting and subsequent chemical doping studies are identified, which generally correspond to the nitrogen and carbon atoms, respectively.

中文翻译：

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在石墨氮化碳基聚合物单层中实现量子限制

石墨氮化碳（g -C ₃ N ₄）因其作为高效无金属光催化剂的潜力而备受关注。这项研究检查了零维量子点的性质演变，直至模拟扩展的g -C ₃ N ₄单层的相当大的簇。我们采用密度泛函理论，使用聚合物单层的“自下而上”结构系统地研究基于g -C ₃ N ₄的三聚氰胺和庚嗪结构单元的结构、电子和光学特性。我们的计算结果表明，基于三聚氰胺和庚嗪的聚合物g-C ₃ N ₄系统必须分别减小到至少 2.74 和 4.00 nm，以观察其光学间隙随着尺寸减小而增加。本研究还通过完整的自然跃迁轨道和状态密度分析，检验了基于g -C ₃ N ₄的单分子层所表现出的电子跃迁的性质。确定了最有希望进行水分解和后续化学掺杂研究的位点，它们通常分别对应于氮和碳原子。