Density functional theory study on (LiNH2)(n) (n=1-5) clusters

作者：Zhou Su Qin; Zhou Su Min; Hu Tao; Ju Xue Hai^*

来源：Journal of Molecular Modeling, 2011, 17(2): 235-242.

DOI：10.1007/s00894-010-0717-5

• (LiNH2)(n) (n=1-5) clusters
• Density functional theory
• Natural bond orbital
• Structure and spectrum
• Bond dissociation energy
• Thermodynamic properties
• Hydrogen storage material

Geometrical structures and relative stabilities of (LiNH2)(n) (n = 1-5) clusters were studied using density functional theory (DFT) at the B3LYP/6-31G* and B3LYP/6-31++G* levels. The electronic structures, vibrational properties, N-H bond dissociation energies (BDE), thermodynamic properties, bond properties and ionization potentials were analyzed for the most stable isomers. The calculated results show that the Li-N and Li-Li bonds can be formed more easily than those of the Li-H or N-H bonds in the clusters, in which NH2 is bound to the framework of Li atomic clusters with fused rings. The average binding energies for each LiNH2 unit increase gradually from 142 kJ mol(-1) up to about 180 kJ mol(-1) with increasing n. Natural bond orbital (NBO) analysis suggests that the bonds between Li and NH2 are of strong ionicity. Three-center-two-electron Li-N-Li bonding exists in the (LiNH2)(2) dimer. The N-H BDE values indicate that the change in N-H BDE values from the monomer a1 to the singlet-state clusters is small. The N-H bonds in singlet state clusters are stable, while the N-H bonds in triplet clusters dissociate easily. A study of their thermodynamic properties suggests that monomer a1 forms clusters (b1, c1, d2 and e1) easily at low temperature, and clusters with fewer numbers of rings tend to transfer to ones with more rings at low temperature. E (g), E (HOMO) and E (av) decrease gradually, and become constant. Ring-like (LiNH2)(3,4) clusters possess higher ionization energy (VIE) and E (g), but lower values of E (HOMO). Ring-like (LiNH2)(3,4) clusters are more stable than other types. A comparison of structures and spectra between clusters and crystal showed that the NH2 moiety in clusters has a structure and spectral features similar to those of the crystal.

• 出版日期2011-2
• 单位南京理工大学; 淮阴工学院