From the very early days of fullerene science, there has been a contant interest in applications of fullerenes and/or nanotubes as agents in materials science in general and in nanotechnologies in particular, especially so in the field of molecular electronics. Since properties and behavior of nano-scale materials are controlled by the quantum-mechanical laws, they should be studied and understood through the quantum-mechanical tools. The computations should clarify conditions for an optimal production of fullerenes and nanotubes of interest and point out the species with especially enhanced application target properties. The computations should provide predictions of the structures, energetics, spectral and optical properties, as well as molecular parameters for evaluation of mechanical, electrical, and other material characteristics. Although most frequently considered endohedral fullerenes for applications in molecular electronics are N@C60 or Li@C60 at present, other metallafullerenes can prove to be equally important. While with the former species, their radical character should be employed in quantum computing, with general metallofullerenes positional isomerism in the metal location should be used. Pristine fullerenes represent a prerequisite in the research. At present over twenty stable fullerenes Cn have been identified with n varying from 60 to 96. Several such mixtures of fullerene isomers have been computed. One of the biggest systems computed so far is C92 with 86 IPR isomers. The reported computations are based on semiempirical (SAM1), ab initio SCF (HF/4-31G), and DFT (B3LYP/6-31G*) approaches and RRHO partition functions. The approach is also applied to smaller fullerenes like C36. As fullerenes are formed at high temperatures, entropy effects are important owing to the temperature enhancement. It turns out for C36 that in the most sophisticated computational approximation used, B3LYP/6-31G*, just two structures are controlling the region of higher temperatures: the conventional fullerenes D6h and D2d. This new type of enthalpy/entropy evaluations can help in the optimized preparations and understanding the material properties and a rational selection of optimal species for nanotechnology applications.
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