ORIGINAL PAPER Computational investigation of interaction of polypyrrole on the surface of single-walled carbon nanotube Manoj K. Shukla & Veera Boddu & Frances Hill Received: 27 May 2014 /Accepted: 4 August 2014 /Published online: 17 August 2014 # Springer-Verlag Berlin Heidelberg (outside the USA) 2014 Abstract A density functional theory investigation of adsorp- tion of monomer, dimer and trimer forms of pyrrole on the outer surface of zigzag (7,0) single-walled carbon nanotube (SWCNT) has been reported. Geometries of the complexes were optimized using the M06-2X functional and the 6- 31G(d,p) basis set. Moreover, 6-311G(d,p), cc-pVDZ and cc-pVTZ basis sets were used for the adsorption energy cal- culation and such energies were corrected for the basis set superposition error. Vertical ionization potential and electron affinity of the investigated system were also computed. The interaction of polypyrrole on the SWCNT surface is charac- terized by the stacking interaction. Adsorption (binding) en- ergy of pyrrole on the SWCNT surface is weak, but such energy increases with the number of monomer units in the pyrrole oligomer. In the SWCNT-pyrrole complexes, the ox- idation and reduction processes will take place only at the SWCNT. The influence of larger unit on the electronic prop- erties of the complex has been detailed. Keywords Electron affinity . Ionization potential . Polypyrrole . Stacking interaction . Zigzag single-walled carbon nanotube Introduction Polypyrrole is a conducting polymer which shows exceptional physical, mechanical, and electrical properties. Therefore, it is not surprising that these properties are explored for various applications such as mechanical actuators and photonic de- vices. The electrical properties of polypyrrole are controlled through suitable doping [1]. Polymer nanocomposites are made up of a polymer matrix and nanofillers [2]. These nanocomposites have potential applications such as in bio- medical applications, electronic devices, aerospace, automo- biles, sporting goods, food packaging, and many more [3–5]. Carbon nanotubes (CNTs) have been found to improve the characteristics of polymers such as mechanical strength, toughness, and elastic modulus [6–8]. The conducting poly- mers and CNT nanocomposites have been synthesized for supercapacitor applications [9–11]. In the CNT based nano- composites, the CNT plays a backbone role, and the conducting polymer is homogeneously distributed in the composites. Pyrrole and pyrrole oligomers have been subjected to sev- eral investigations determining various properties including electronic structure, vibrational frequencies, ionization poten- tial, and electron affinity and effect of doping on these prop- erties [12–14]. It has been found that aromatic compounds are adsorbed on CNT surfaces through stacking interactions [15–20]. The current research is prompted from the aspiration to investigate electromechanical properties of bio-inspired polymer nanocomposites and model mechanisms of switching under electrical stimuli [21]. Carbon nanotubes may be used to modify the response of polypyrrole under electric stimuli [22]. The mechanical properties of these composite materials can be controlled by electrical or electrochemical switching mecha- nisms and these nanocomposite polymers may have applications in sensors and mechanical actuators [23–25]. Inspired by the stimulus-responsive behavior of sea cucumber dermis switching Electronic supplementary material The online version of this article (doi:10.1007/s00894-014-2414-2) contains supplementary material, which is available to authorized users. M. K. Shukla (*) : F. Hill Environmental Laboratory, US Army Engineer Research and Development Center, 3909 Halls Ferry Road, Vicksburg, MS 39180, USA e-mail: Manoj.K.Shukla@usace.army.mil V. Boddu (*) Environmental Processes Branch, Installations Division, US Army ERDC-CERL, Champaign, IL 61826, USA e-mail: Veera.Boddu@usace.army.mil J Mol Model (2014) 20:2414 DOI 10.1007/s00894-014-2414-2