1) From bulk structure of silicon, the structure for the slab model of Si surface can be easily built using VNL;
the axis direction of silicon nanowire <====> the <hkl>, i.e., the Miller index of Si surface;
the diameter of silicon nanowire (or the size of cross section of nanowire) <====> the unit cell of slab model of Si surface.
the shape of cross section of silicon nanowire is adjusted by selectively removing some atoms in the created structure of slab model.
2) The surface passivation can be achieved by adding some H atoms with the Molecular builder of VNL.