(Color) (a) Crystal structure of bulk CuO is composed of interlocking sheets of approximately square Cu-O units that are joined by Cu-O bonds involving the Cu dz2 orbitals. (b) Individual sheets are connected to those above and below them by Cu-O bonds. (c) Rearranging some atoms (e.g., the O in the upper left) and some bonds (e.g., upper left and lower right) allows for the formation of approximately square planar CuO sheets. These can be “rolled up” to form the nanobarrels shown in Figs. 2 and 3 .
(Color) Nanobarrels with diameters of (a) (CuO)3, (b) (CuO)4, (c) (CuO)5 and (d) (CuO)6 are shown for a length of six rings. Note that the barrels tend to be somewhat smaller in cross-section at the ends than at the middle.
(Color) Nanobarrels with diameters of (CuO)6 are shown for lengths varying from (a) one ring to (f) six rings. On the average, increasing the length of the barrel diminishes the average edge effects from the unbonded orbitals at the ends of the barrel.
(Color) Binding or cohesive energy per CuO unit is shown for several series of barrels ((CuO)3, (CuO)4, (CuO)5 and (CuO)6) as a function of their length in terms of rings or “hoops.” Note that on the average, longer barrels have greater stability as do wider barrels within the range that we studied.
(Color) Density of states (in st./Ha.) is shown as a function of binding energy (in eV) for a CuO nanobarrel with 24 CuO units in four six-fold rings. Note the band gap between about −4.5 and −3.0 eV. Note also the unoccupied states just above the Fermi level that arise from the O 2p and Cu 3d orbitals.
(Color) Spin density is shown for a CuO nanobarrel containing 20 CuO units (i.e., 40 atoms). The overall spin (Hirshfield) appears to be +2. The spin can be located at either the ends of the barrel, as in this case, spread across the whole barrel, or located on the ends, as in Fig. 7 .
(Color) Spin density is shown for a CuO nanobarrel containing 36 CuO units (i.e., 72 atoms). The overall spin (Hirshfield) appears to be 0, and apparently the spins cancel each other out.
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