A Direct Molecular Orbital–Molecular Dynamics (MO–MD) Study on the Diffusion of Alkaline Ions on Amorphous Carbon

Abstract

Hybrid density functional theory (DFT) calculations have been carried out for the lithium ion-carbon cluster model systems to elucidate the nature of lithium-carbon surface interaction. Also, direct molecular orbital-molecular dynamics (MO–MD) calculation [Tachikawa and Shimizu, J. Phys. Chem. B, 109 (2005) 13255] was applied to diffusion processes of the Li ion on the model surfaces of amorphous carbon. Seven cluster models (n = 7, 14, 19, 29, 37, 44 and 55, where n means numbers of rings in the carbon cluster models) were considered in the present study. The B3LYP/LANL2MB calculations showed that the lithium ion is located at ca. 1.60 Å from the carbon surface. The direct MO–MD calculations showed that the Li ion diffuses freely on the surface above 250 K. At higher temperature (1100 K), the Li ion moves from the center to edge region of the model surface and leaves from the surface. The nature of the interaction between Li⁺ and the carbon clusters was discussed on the basis of theoretical results.

Keywords:

• amorphous surface
• charge distribution
• DFT
• diffusion of lithium and sodium ions

Acknowledgments

The authors are indebted to the Computer Center at the Institute for Molecular Science (IMS) for the use of the computing facilities. H.T also acknowledge a partial support from a Grant-in-Aid from the Ministry of Education, Science, Sports and Culture of Japan.

Notes

^a Structures are optimized at the B3LYP/LANL2MB level.