Research Article Electronic Transport Properties of Doped C 28 Fullerene Akshu Pahuja and Sunita Srivastava Department of Physics, Panjab University, Chandigarh 160014, India Correspondence should be addressed to Akshu Pahuja; akshuh@yahoo.com Received 21 August 2014; Revised 19 October 2014; Accepted 11 November 2014; Published 26 November 2014 Academic Editor: Yuan Ping Feng Copyright © 2014 A. Pahuja and S. Srivastava. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Endohedral doping of small fullerenes like C 28 afects their electronic structure and increases their stability. Te transport properties of Li@C 28 sandwiched between two gold surfaces have been calculated using frst-principles density functional theory and nonequilibrium Green’s function formalism. Te transmission curves, IV characteristics, and molecular projected self-consistent Hamiltonian eigenstates of both pristine and doped molecule are computed. Te current across the junction is found to decrease upon Li encapsulation, which can be attributed to change in alignment of molecular energy levels with bias voltage. 1. Introduction Te last few decades of the twentieth century witnessed an upsurge in development of electronics based on molecular devices [1]. Electrical measurements on single molecules embedded between electrodes have attracted special atten- tion [2–5]. Electron transport across such molecular junc- tions gives rise to interesting phenomena like negative difer- ential resistance, rectifcation, single electron characteristics [5–7], and so forth. Tis has resulted in their application as feld efect transistors [8], logic gates [9], switches [10], and sensors [11]. Numerous attempts have been made to investigate transport properties of a fullerene molecule [12– 14]. A fullerene molecule possesses unique structural and electronic properties, and its role as a functional electronic device [15, 16] has been widely analyzed. Te transport properties of a fullerene molecule are infuenced by its orientation between the electrodes [17], the nature of contact with the electrodes [18], and also on the type of doping and nature of dopant [19, 20]. An et al. found that insertion of Li into C 20 cage improves its transmission capacity and increases the equilibrium conductance by about 66.67% [21]. Zhang et al. revealed that the conductivity for the doped C 60 fullerene is higher than that of the pristine fullerene [22]. Te spin-resolved transport properties of C 28 molecule sandwiched between Au electrodes with diferent contact confgurations have been examined theoretically [14]. C 28 is the smallest fullerene that has been found to be experimen- tally signifcant [23, 24]. Since C 28 molecule is very active, it can form particularly stable endohedral complexes [25– 27]. Guo et al. found that empty C 28 fullerene behaves as a hollow tetravalent superatom with tetrahedral symmetry [28]. It was proposed that metals with electronegativities smaller than 1.54 should form endohedral fullerenes larger than a minimum size, which depends on the radius of the trapped atom. Based on the above size and electronegativity considerations, it should be possible to encapsulate Li atom in C 28 cage. Insertion of Li atom in a smaller fullerene molecule has been found to increase its conductivity [21], and also endohedral derivatives of fullerene molecules based on Li have been investigated [29, 30]. In this work we undertake the study of transport properties of endohedral fullerene Li@C 28 sandwiched between Au (111) electrodes using a frst- principles computational method based on density func- tional theory in combination with nonequilibrium Green’s function theory. Doping can efectively change the electronic properties of fullerenes and hence provides an opportunity to modify transport properties as well. Tus we attempt to understand the efect of single-atom change on transport properties of C 28 fullerene. Te transmission spectra at diferent bias voltage and IV characteristics are plotted and compared for both pure and doped C 28 molecules. Hindawi Publishing Corporation Physics Research International Volume 2014, Article ID 872381, 7 pages http://dx.doi.org/10.1155/2014/872381