| The research of the endohedral fullerenes has been focused on the embedded single,double atoms and compound. With the variety of the fullerene clusters, high restriction for fullerene structures is required. At present, suitable carbon cages for material embedding, properties of varied endohedral fullerenes and practical application of fullerenes become the research focus in recent years. The study of the properties of the endohedral fullerene is mainly focused on activity, possible application and possibility of synthesis. At present, the eperimental and computational studies are mainly concentrated on group two and three of transitional elements. In this work, La and Sc endohedral fullerenes were discussed. According to the stability of the endohedral fullerene and the possibility of the actual synthesis, large scale fullerenes(Cn >100)were discussed.The rare earth elements represented by La and Sc have good application perspective in optical, material and biological medicine. C112 was selected as the computational model, 860161 IPR and NIPR C112 isomers were obtained using Ca Ge.For NIPR isomers, only isomers with PA ￡ 2 were screened according to the rule of PAPR(adjacency penalty rule). DFTB method was performed to optimize 3324 IPR isomers, isomers with energy difference within 10Kcal/mol were screened. 100low-energy IPR C112 isomers were then refined by B3LYP/3-21 G method, where the most stable isomer is the IPR D2:860117.To calculate the structure and properties of endohedral fullerenes, C112 with six negative charges were taken into account. All of IPR isomers and 129073 NIPR isomers were optimized under the B3LYP/3-21G// B3LYP/6-31G* level.Lowest-energy five IPR and NIPR isomers were obtained under the criterion of energy difference within10Kcal/mol respectively. The most stable C112-6 isomer is C2:860078. For the IPR fullerenes, the lowest-energy embedded position is metal located on both sides of the axis relative to the six membered ring inside, with respect to the NIPR fullerenes, the lowest-energy embedded positions metal are located on both sides of the five-five rings connection and the position relative to the six membered ring inside. After selecting theposition, metal La2 and Sc2 were embedded in the first five stable C112-6 structures, respectively. The single point energy of La2@C112 and Sc2@C112 were calculated, both of the most stable structure are the C112(C2:860078) obeying IPR rule.Frequency calculations showed that the 10 lowest-energy endohedral fullerenes were minima on potential energy surface. The thermal concentration curve of La2@C112 within 3000 K was obtained using the distribution function. The maximum isomer concentration is La2@C2:860078 in the range of 500-1400 K. The concentration decreases monotonically with the temperature increase. Concentrations of La2@C2:860136 and La2@C2:860078 were similar at 1400 K. After 1400 K, the concentration of La2@C2:860136 overcomes La2@C2:860078 and become the maximum of all isomers. As seen from the thermal concentration curve of Sc2@C112, between 0 K and 4000 K, the concentration of Sc2@C112 is the largest, which decreases monotonically with temperature increase. The concentration of Sc2@D2:860117 increased with the increase of temperature, and reached the maximum value of 28.4% at 1354 K. Then the temperature continued to rise, the concentration of Sc2@D2:860117 began to decrease and value keeps at 14.7% after 3000 K. Infrared and Raman spectra provide fingerprint identification for different isomers. At 1620 cm-1, La2@C2:860078(IPR) has a characteristic fingerprint peak. La2@Cs:854341(NIPR) fingerprint peak is at 1440 cm-1. The characteristic peaks of Sc2@D2:860117(IPR) and Sc2@C1:859163 are at 1430 cm-1 and 1493.87 cm-1 respectively. The three-order nonlinear responses of C112 were calculated by ZINDO-SOS method. TPA, DFWM and THG responses of the five lowest-energy isomers were calculated, large response values of them indicating these isomers are good candidates for nonlinear optical materials. |
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