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A new method of theoretical modelling of polyhedral single-walled nanotubes based on the consolidation of walls in the rolled-up multi-walled nanotubes is proposed. Molecular mechanics and ab initio quantum mechanics methods are applied to investigate the merging of walls in nanotubes constructed from the different phases of titania. The combination of two methods allows us to simulate the structures which are difficult to find only by ab initio calculations. For nanotube folding we have used (1) the 3-plane fluorite TiO2 layer; (2) the anatase (101) 6-plane layer; (3) the rutile (110) 6-plane layer; and (4) the 6-plane layer with lepidocrocite morphology. The symmetry of the resulting single-walled nanotubes is significantly lower than the symmetry of initial coaxial cylindrical double- or triple-walled nanotubes. These merged nanotubes acquire higher stability in comparison with the initial multi-walled nanotubes. The wall thickness of the merged nanotubes exceeds 1 nm and approaches the corresponding parameter of the experimental patterns. The present investigation demonstrates that the merged nanotubes can integrate the two different crystalline phases in one and the same wall structure.

Wurtzite-structured zinc oxide (ZnO) is not only a typical n-type semiconductor with a direct band gap of 3.3-3.4 eV but it also possesses a number of properties which can be used in key technological applications [1, 2], e.g. photocatalysis [3]. One of the most important applications is piezoelectricity, known as an effect of the electrical potential production (electron charge polarization) under external mechanical stress outside the crystal which does not possess central symmetry (e.g. w-ZnO) [4,5]. Transformations of mechanical to electrical energy and vice versa are realized in a number of piezoelectric devices as well as in alternative electromechanical devices like micro-generators [6], transducers [7], actuators [8], etc, dealing with material elasticity and other mechanical properties. On the other hand, being reduced to nanoscale dimensions, for example, 2D nanothin films or 1D nanowires (NWs), the majority of materials can significantly change their behaviour compared with what they exhibit at macroscales (this also means, that bulk properties cannot be directly used for a proper description and modelling of the corresponding nanoscale systems). A variety of nanoelectromechanical systems based on NWs have been demonstrated recently [5,9], where not only their mechanical properties have attracted enhanced interest but their tribological properties too (connected with friction, wear, adhesion and lubrication in nanoscale systems) although the latter has been significantly less studied so far.Obviously, separately synthesized (not bundled) NWs, the shape and geometry parameters of which can be directly estimated using either atomic force microscopy [10] or inside a scanning electron microscope (SEM) [11], are quite attractive objects for nanotribomechanical studies [9], and can provide certain benefits as compared to

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