Electronic properties of disordered functionalized carbon nanotubes

Carbon nanotubes (CNTs) present important electronic, mechanical and optical properties. These properties can be different compared to the pristine nanotube when its surface is functionalized. These changes can be explored in research and application areas such as building nanodevices that act like sensors and filters. Following this idea, in this work we made a systematic study of the influence of two type of functionalization groups −OH and −COOH at different concentrations (5, 10, 15, 20 and 25%) of the surface atoms (higher concentrations were avoided due to possible steric effects). The methodology used consists in create an script that add, randomly, the functionalization groups to the surface of a (10,0) single wall CNT. In this way, we generated 10.000 structures for each concentration and selected the representative ones according the disorder created. To accomplish this, the quasi-entropy of each generated  structure was calculated using the USPEX software. All the calculations were performed using semiempirical PM7 method as implemented in the software MOPAC. For the representative structures, the highest occupied molecular orbital energy (∈H), the lowest unoccupied molecular orbital energy (∈L), the electronic gap (∆E), the chemical potential (µ), the molecular hardness (η), the electrophilicity index (ω) and the electrostatic potential were calculated. Other parameters like heat of formation, entropy, area and volume were also determined. From the obtained results we were able to correlate each calculated property with the type and concentration of the functionalization groups. From these correlations it is possible to select a priori type of functionalization and its concentration accordingly the desired property.