The potential energy surfaces of Li + -diglyme and Li + -triglyme complexes, which are models for poly-(ethylene oxide) electrolytes, have been investigated at the HF/6-31G(d) and MP2/6-31+G(d) levels of theory. Eighteen local minima were located that correspond to coordination of Li + with one to four oxygens. The binding energies of the complexes increase with coordination of Li + by oxygen, although the binding per Li-O bond decreases. The potential energy surfaces for lithium cation migration between one-and twocoordination sites and two-and three-coordination sites in the Li + -diglyme complexes were investigated, and five transition states were located. While the barriers are small (less than 2 kcal/mol) for lithium cation migration from lower to higher coordination, the barriers are large (20-30 kcal/mol) for higher to lower coordination. The latter corresponds to the barrier for transfer of Li + from one end of diglyme to the other and is approximately the difference in binding energy of the higher and lower coordination structures. The implications for Li + migration along a single polymer chain in lithium-poly(ethylene oxide) are discussed.

The lithium ion migration mechanism in Li+−(diglyme)2 and LiClO4−diglyme complexes with coordination of Li+ by 3 to 6 oxygens has been investigated using ab initio molecular orbital theory. Local minima corresponding to different coordination sites of the Li+ cation and transition states between them have been located. The Li+ binding energies of the Li+−(diglyme)2 and LiClO4−diglyme complexes range from 94 to 122 and 167 to 188 kcal/mol, respectively. The binding energies increase with increasing coordination of Li+ by oxygen, although the binding per Li−O bond decreases, and structures with higher coordination of Li+ by oxygen exhibit longer Li−O bond lengths than the ones with lower coordination number. The barrier heights for n + 1 → n coordination of the cation by oxygen decrease with increasing coordination number n, with the smallest Li+ migration barriers (7−11 kcal/mol) occurring for complexes with the highest coordination numbers. The reaction coordinate for lithium ion migration between coordination sites is the torsional motion of the diglyme backbone. The implications of these results for Li+ migration in lithium poly(ethylene oxide) melts are discussed.

Unrestricted Hartree-Fock calculations coupled with second-order M~ller-Plesset correlation correction were performed to study the structures and energetics of microclusters. For (BN)?, linear and rhombus forms are almost isoenergetic, whereas cyclic forms are preferable for (BN)3 and (BN)4 clusters. As a general trend, linear isomers prefer the triplet spin state, whereas cyclic isomers prefer the singlet spin state. Total charge density plots show a strong dominance of the B-N bond, indicating that the extent of its polar character becomes stronger with the increase in the cluster size. The loss of a BN monomer is shown to be the most likely fragmentation channel for both neutral and single-ionized clusters. We find that neutral (BN)" clusters have the same structural configurations as those of their corresponding C2n counterparts. This similarity follows the isoelectronic principle and is of importance due to recent interest in the investigations of BN fullerene analogs.

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Results of ab initio Hartree-Fock calculations for the electronic structure of aluminum nitride in the (high-pressure) rocksalt phase are reported. In the rocksalt phase, the calculated lattice constant is 3.982 A with the bulk modulus of 329 GPa. The band structure is predicted to be indirect at the X point with a gap of 8.9 eV. In this phase, the bonding is shown to be essentially ionic between Al and N. The direct gap shows a stronger linear dependence on pressure with a pressure derivative of 68 meV/GPa compared to that of the indirect gap with a pressure derivative of 31.7 meV/GPa.