基于曲率和电子结构的掺杂C50和C70富勒烯的稳定性研究

使用密度泛函理论(DFT)-B3LYP/6-31G^*方法研究了B、N、Si、P和Co在C₅₀和C₇₀中的掺杂能和电子结构, 并基于曲率理论和电子结构探讨了掺杂富勒烯的结构稳定性. 计算结果表明, 掺杂能随着原子曲率的增大而减小, 随着掺杂物种原子半径的增大而增大, B、N、P和Co的掺杂有利于C₅₀结构的稳定, 而B和N的掺杂不利于C₇₀结构的稳定; 除了用于反映原子活性的曲率主要决定掺杂反应性, 各不等价碳原子在C₅₀和C₇₀的最高占据分子轨道(HOMO)中所占成分对掺杂能的影响也很大, 且其成分越大越有利于掺杂. 此外, 掺杂原子得失电子情况与其电负性有关. 本工作将为富勒烯结构稳定性的研究提供理论依据.     

Transitional Area of Ce~(4+) to Ce~(3+) in Sm_xCa_yCe_(1-x-y)O_(2-δ) with Various Doping and Oxygen Vacancy Concentrations: A GGA + U Study

In this work,we perform DFT+U periodic calculations to study geometrical and electronic structures and oxygen vacancy formation energies of Sm_xCa_yCe_(1-x-y)O_(2-δ)systems(x=0.0312,0.0625,0.125 and 0.250;y=0.0312,0.0625,0.125 and 0.250;δ=0.0312,0.0625,0.125,0.250 and 0.50)with different oxygen vacancy and doping concentrations.The calculated results show that the V_1-Sm~(3+)-V_2 structures where there is a position relationship of the face diagonal between V_1 and V_2 both nearest to Sm~(3+)have the lowest energy configurations.The study on electronic structures of the Sm_xCa_yCe_(1-x-y)O_(2-δ)systems finds that excess electrons arise from oxygen vacancies and are localized on f-level traps of their neighbor Ce,and Ca~(2+)and Sm~(3+)co-doping effectively restrains the reduction of Ce~(4+).In order to avoid the existence of Ce~(3+),x and y must be both larger than 0.0625 asδ=0.125 orδmust be smaller than 0.125 as x=y=0.0625.The Ce~(3+)/Ce~(4+)change ratio k has an obvious monotonous increase with increasing the vacancy oxygen concentration.The introduction of Sm~(3+)decreases k.In addition,the doped Sm~(3+)can restrain the reduction of Ce~(4+)when the V_1-Sm~(3+)-V_2 structure with a face diagonal position relationship in lower reduced atmosphere exists.It need be pointed out that the Sm_(0.25)Ce_(0.75)O_(1.5) system should be thought of as a Sm-doped Ce_2O_3 one.