Li2 trapped inside tubiform [n] boron nitride clusters (n=4-8): structures and first hyperpolarizability.

The geometries and electronic properties of tubiform [n] boron nitride clusters entrapping Li(2) (Li(2)@BN-cluster(n,0); n=4-8), obtained by doping BN-cluster(n,0) with Li(2) molecules, are investigated by means of DFT. The effects of tube diameter n on the dipole moment μ(0), static polarizability α(0), and first hyperpolarizability β(0) are elucidated. Both the dipole moment and polarizability increase with increasing tube diameter, whereas variation of the static first hyperpolarizability with tube diameter is not monotonic; β(0) follows the order 1612 (n=4)<3112 (n=5)<5534 (n=7)<8244 (n=6)<12,282 a.u. (n=8). In addition, the natural bond orbital (NBO) charges show that charge transfer takes place from the Li(2) molecule to the BN cluster, except for BN-cluster(8,0) with larger tube diameter. Since the large-diameter tubular BN-cluster(8,0) can trap the excess electrons of the Li(2) molecule, Li(2)@BN-cluster(8,0) can be considered to be a novel electride compound.