Virtual NanoLab includes the Nanotube Grower tool, designed for creating and previewing single-wall carbon nanotubes. In addition, the tool automatically computes and displays a preview of the tight-binding band structure of the nanotube.

The Nanotube Grower is opened by double-clicking its icon on the Toolbar.

A nanotube is defined by three parameters:

These parameters are specified in the upper left panel of the Nanotube Grower window. The lower left panel displays some calculated tube properties, such as tube radius, period length along the tube axis direction, as well as information about the conductance properties of the tube. This information is automatically updated as the tube parameters are modified.

The geometric structure of the nanotube is displayed in the Preview window to the right. However, unlike the 3D window in many other VNL tools, the Nanotube Grower does not update the window until you left-click the Show button since the number of atoms can become large for certain tube indices, which would compromise the performance. By right-clicking the preview window, it is possible to adjust the parameters of the atomic configuration plot similar to the functionality of the Nanoscope tool.

The tight-binding band structure near the Fermi level of the nanotube is automatically computed on the fly, and can be viewed on the Band Structure tab. Zoom in by drawing a rectangle with the mouse; to zoom out, right-click the plot and use the context menu, from which the plot also can be printed or exported.

The band structure is calculated using a third-nearest neighbor approximation, which gives realistic results, even though it fails to account for small band gaps induced by the coupling between s and p bonds. This effect is due to the curvature of the tube in semi-metallic tubes, that is, tubes where n-m is an integer multiple of 3. The value given for the band gap in the Tube Properties panel to the left is calculated using an empirical analytic expression, which takes this curvature effect into account.

To store a carbon nanotube configuration on disk as a NanoLanguage script, use the Save or Save As button.

If you want to revert to the default nanotube with the indices (4,1), you can left-click the Restore Defaults button. To exit the Nanotube Grower without saving the system, simply close the window. The created system may, for example, be used to create a two-probe system in the Atomic Manipulator, or it may be dropped on the NanoLanguage Scripter for performing a DFT computation of the band structure.

Dropping the created nanotube NanoLanguage script on the Atomic Manipulator tool gives you the possibility to edit the unit cell parameters in the transverse plane, to cleave the tube and include it in a two-probe system, and change the atoms in the basis. The latter option provides you with the possibility of constructing, for example, silicon based nanotubes.