  The electronic structure of CdSe/CdS core/shell seeded nanorods of
experimentally relevant size is studied using a combination of molecular
dynamics and semiempirical pseudopotential techniques, with the aim to address
the transition from type-I to a quasi-type-II band alignment. The hole is found
to be localized in the core region regardless of its size. The overlap of the
electron density with the core region depends markedly on the size of the CdSe
core: For small cores, we observe little overlap, consistent with type-II
behavior. For large cores, significant core-overlap of a number of excitonic
states can lead to type-I behavior. When electron-hole interactions are taken
into account, the core-overlap is further increased. Our calculations indicate
that the observed transition from type-II to type-I is largely due to simple
volume effects, and not to band alignment.
