C $_{24}$碳团簇的氢化：结构多样性和能量性质
Hydrogenation of C$_{24}$ carbon clusters : structural diversity and energetic properties
摘要：
本工作的目的是探索的势能面的C $_{24}$ H $_n$ {n= 0，6，12，18，24}高达20- 25\，eV的密度泛函的紧密结合（DFTB）势相结合的遗传算法。非碎片化结构的结构多样性进行了分析，使用序参量，其中被选为5或6个碳环的数量和非球面常数$β$。最丰富和最低的能量人口被发现对应于一个薄片人口，拥有大量的5或6-碳环的可变形状的异构体构成。当$n_H/n_C$增加时，该群体的特征在于球形异构体的数量更多。同时，由具有较少5或6个碳环的球形异构体构成的椒盐脆饼人口的分数增加。对于所有氢化速率，笼群的分数保持非常小，而支化群是所有$n_H/n_C$比率的最高能量群。对于所有的C $_{24}$ H $_n$ {n= 0，6，12，18，24}团簇，详细研究了碳环尺寸分布随能量的演化，清楚地表明稳定性与6-碳环的数目有关。对杂交$sp^n$（n=1-3）的类似研究表明，$sp^1$碳原子的数目随能量增加，而总体上$sp^3$碳原子的数目随$n_H/n_C$增加。随着$n_H/n_C$的增加，所有布居的电离势的平均值都降低，从7.9\，eV下降到6.4\，eV，我们将其与碳原子杂化$sp^n$（n=1-3）进行了关联。这些结果是天体物理学的兴趣，因为它们应该考虑到在天体物理模型，特别是关于气体电离中的碳物种的作用。
英文摘要：
This work aims at exploring the potential energy surfaces of C$_{24}$H$_n${n=0,6,12,18,24} up to 20-25\,eV using the genetic algorithm in combination with the density functional based tight binding (DFTB) potential. The structural diversity of the non fragmented structures was analysed using order parameters which were chosen as the number of 5 or 6 carbon rings and the asphericity constant $β$. The most abundant and lowest energy population was found to correspond to a flakes population, constituted of isomers of variable shapes possessing a large number of 5 or 6-carbon rings. This population is characterized by a larger number of spherical isomers when $n_H/n_C$ increases. Simultaneously, the fraction of the pretzels population constituted of spherical isomers possessing fewer 5 or 6 carbon ring cycles increases. For all hydrogenation rates, the fraction of cages population remains extremely minor while the branched population is the highest energy population for all $n_H/n_C$ ratios. For all C$_{24}$H$_n${n=0,6,12,18,24} clusters, a detailed study of the evolution of the carbon ring size distribution as a function of energy clearly shows that the stability is correlated to the number of 6-carbon rings. A similar study for hybridization $sp^n$ (n=1-3) shows that the number of $sp^1$ carbon atoms increases with energy while globally the number of $sp^3$ carbon atoms increases with $n_H/n_C$. The average values of the ionization potentials of all populations were found to decrease when $n_H/n_C$ increases, ranging from 7.9\,eV down to 6.4\,eV that we correlated to carbon atoms hybridization $sp^n$ (n=1-3). These results are of astrophysical interest as they should be taken into account in astrophysical models especially regarding the role of carbonaceous species in the gas ionization.
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