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A previously developed method for self-consistent-field density-functional calculations involving a variational fit to the charge density is generalized to the case in which the total (electronic plus nuclear) Coulomb potential is fit. on atomic neon, the superiority of variational over conventional least-squares-fitting methods is demonstrated.

Many single-wall carbon nanotube (SWNT) properties near the Fermi level were successfully predicted using a nearest-neighbor tight-binding model characterized by a single parameter, V1. We show however that this model fails for armchair-edge graphene nanostrips due to interactions directly across hexagons. These same interactions are found largely hidden in the description of SWNTs, where they renormalize V1 leaving previous nearest-neighbor model SWNT results largely intact while resolving a long-standing puzzle regarding the magnitude of V1.