Optimized atomic-like orbitals for first-principles tight-binding molecular dynamics

We analyze the optimization of atomic-like minimal basis sets for the hydrocarbons and for materials made up only of C atoms, e.g. C-nanotubes. In our approach the optimized numerical atomic orbitals (NAOs) are obtained as a linear combination of only two primitive NAOs. We find that the optimized basis sets yield an important lowering of the total energy, and bondlengths in very good agreement with the experimental evidence. Also, we find that a good "universal" minimal basis set for the hydrocarbons and C-only materials can be obtained using this simple method. The approach discussed in this paper is a promising tool for the simulation of complex organic materials, beyond the hydrocarbons, using optimized minimal basis sets. (c) 2006 Elsevier B.V. All rights reserved.