A DFT Prediction Of The Interstellar Molecular Candidate NC_2nN^0,±1(n=1-4) And Magnetic Silicon Nanotube Eu₂@Si₃₀

As one of the four biggest discoveries in the field of astronomy in 1960s, researches and observations of interstellar molecules have been made significant progress. Defining and seeking for new, complex interstellar organic molecules and understanding their evolutionary process have become a hot topic for astronomical, physical and chemical scientific workers. Cage-like clusters have attracted a great deal of interest since the discovery of C60. Since silicon is as a key element in the semiconductor industry, it is of great interest to determine whether or not Si can form fullerene-like structures.The exchange-correlation interaction was treated within the generalized gradient approximation (GGA) using the Becke exchange functional and the Lee-Yang-Parr correlation funcional (BLYP) exchange-correlation functionals were chosen to carry out the widely search, and prediction of properties, vibrational frequencies and infrared intensity of potential interstellar molecules NC_2nN(n=1-4). The geometry optimization and properties prediction of low-lying isomers of NC_2nN^(0,±1)(n=1-4) have been studied in this paper. At the DFT-GGA/PW91 level, we investigate the origin of the stability of the silicon fullerene Eu2@Si30 encapsulating two Eu atoms, and the properties of the Si-Si chemical bonds. The goal is to understand the role that the rare-earth element plays in stabilizing the silicon fullerenes.â… The lowest-energy structures of NC_2nN(n=1-4) are linear-like N-Cm-N, with two nitrogen atoms occupying the ends of the carbon chain, forming triplebond of C≡N. When n=1, the structures of NC2N is linear, but when n=2, 3, 4, the structure of NC_2nN become a little bent. The structures of NC_2nN+(n=1-4) and NC_2nN^—(n=1-4) have the similar structures of the neutral NC_2nN(n=1-4).â…¡Dipole moments of NC_2nN(n=1-4) series are lesser. According to the neutral structures, the dipole moments of NC_2nN+(n=1-4) and NC_2nN^—(n=1-4) are much higher, except for the NC₆N⁺ and NC₆N^—. The highest dipole moments of the charged ions is NC4N⁺ for cations and NC4N^—for anions, with the dipole moments 7.03 debye and 7.04 debye respectively.â…¢The length of triplebonds both C≡N and C≡C increases a little with the length of the carbon chain increases, and the length of single bonds of C-C decreases a little with the length of the carbon chain increases. When the carbon chains have the same size, the length of both C≡N and C≡C is the neutral< the cationic< the anionic, and the length of single bonds of C-C is the neutral> the cationic> the anionic.â…£The harmonic vibrational analysis of NC_2nN^(0,±1)(n=1-4) has been discussed in this paper. For the neutral structures, the highest peaks correspond to the frequencies at 271.9cm^-1 for NC₂N, 2229.7cm^-1 for NC₄N, 2262.8cm^-1 for NC₆N and 2238.7cm^-1 for NC₈N, and the corresponding intensity is 20.25km/mol,14.28 km/mol, 61.28 km/mol and 133.14 km/mol, respectively. For the cationic structures, the highest peaks correspond to the frequencies at 1868.8cm^-1 for NC₂N⁺, 2096.8cm^-1 for NC4N+, 2168.2cm^-1 for NC6N+ and 2161.8cm^-1 for NC8N+, and the corresponding intensity is 291.99km/mol,502.84 km/mol, 655.30 km/mol and 874.84 km/mol, respectively. For the anionic structures, the highest peaks correspond to the frequencies at 1764.7cm^-1 for NC₂N^—, 2032.8cm^-1 for NC₄N^—, 2103.5cm^-1 for NC₆N^—and 2116.1cm^-1 for NC₈N^—, and the corresponding intensity is196.28km/mol,619.60 km/mol, 1270.87 km/mol and 2035.31 km/mol, respectively.â…¤The geometries and stabilities of Eu2Si30 clusters have been calculated at the GGA/PW91 level. The results indicate that the rare earth atom, europium, can stabilize the Si₃₀ fullerene cage. Our results show that two stable isomers of Eu-encapsulated silicon clusters, a cage-like structure and a tube-like structure, are stable, but have completely different structures and magnetic properties. Electronic structure analysis shows that sp²-like hybridizations induced by the europium atoms can make the fullerene-like silicon cage more stable. Furthermore, with D_5h-symmetry and a high spin moment of nearly 10μB, Tube may be a potential embryo for manufacturing longer silicon nanotubes, and may have potential applications in the fields of spintronics and high-density magnetic storage.