ISSN 1068-3356, Bulletin of the Lebedev Physics Institute, 2017, Vol. 44, No. 5, pp. 151–153. c  Allerton Press, Inc., 2017. Original Russian Text c  A.V. Osadchy, E.D. Obraztsova, V.V. Savin, and Yu. P. Svirko, 2017, published in Kratkie Soobshcheniya po Fizike, 2017, Vol. 44, No. 5, pp. 44–49. Computer Simulation of Edge-Terminated Carbon Nanoribbons A. V. Osadchy a,b , E. D. Obraztsova a,b , V. V.Savin c , and Yu. P. Svirko d a Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia; e-mail: aosadchy@kapella.gpi.ru b National Research Nuclear University “MEPhI”, Kashirskoe sh. 31, Moscow, 115409 Russia c Immanuel Kant Baltic Federal University, ul. Nevskogo 14, Kaliningrad, 236041 Russia d University of Eastern Finland, Yliopistokatu 2, FI-80101 Joensuu, Finland Received September 29, 2016 Abstract—In this paper, we present the results of ab initio simulation of edge-terminated carbon nanoribbons (CNRs). The calculations were performed using the electron density functional theory with the expansion of electron wave functions in plane waves in the Quantum Espresso software package [1]. The effect of various edge termination types on the band structure of graphene nanoribbons is studied. The data obtained showed that hydrogen and fluorine termination has a very weak effect on the structure. Sulfur or bromine termination causes a semiconductor-to-metal transition. The cause of the change in the conductivity type is the appearance of the electron dispersion curve crossing the nanoribbon band gap. At the same time, the dispersion dependences of the ribbon edge-terminated with alternating chlorine and hydrogen atoms do not exhibit such a change, and the curve mentioned above is not observed. The causes of the observed effects are analyzed. DOI: 10.3103/S1068335617050074 Keywords: carbon, nanoribbons, band structure, simulation. Introduction. Recently, carbon nanoribbons again began to attract researchers’ attention. Nanorib- bons represent ribbons to 20 nm wide cut from a graphene sheet. Interest is mainly caused by synthesis of carbon nanoribbons placed into single-walled carbon nanotubes [2, 3]. Carbon nanotubes represent a material with unique electronic and optical properties; at the same time, they can be containers for developing new (often not existing in a free state) materials. One of the most interesting type of such materials is carbon nanoribbons. Diameters of single-walled carbon nanotubes vary from 0.4 to 3 nm [4]. This leads to the possibility of synthesizing nanoribbons placed into single-walled carbon nanotubes of different widths [2, 3]. The published theoretical results [5] show that the band structure of nanoribbons placed into nanotubes is almost independent of the structure of isolated nanoribbons. At the same time, it should be noted that, in contrast to carbon nanotubes, nanoribbon edges have dangling bonds which are terminated with hydrogen atoms in most published theoretical works. However, under conditions of practical synthesis of samples, such bonds can be terminated by various atoms and functional groups, which can have a significant effect on properties of a material under study. This study is devoted to the variation features of the band structure of graphene nanoribbons terminated with various atoms and functional groups and to the causes of the observed effects. Methods. Computer simulation of graphene nanoribbons passivated by various atoms and functional groups was performed using the electron density functional method. The electron wave functions were expanded in the plane-wave basis. To minimize the basis dimension, the pseudopotential method was used. The studies performed showed that the best results on the band structure, equilibrium cell parameters, and interatomic distance are achieved using the ultrasoft pseudopotential. The basis cutoff energy was 80 Ry. To determine the equilibrium crystalline geometry, the BFGS algorithm was used. The geometry was optimized in two steps. In the first step, ion positions were relaxed to a limit, when interatomic forces did not become less than 10 -4 Ry/a.u. The second cell parameter relaxation stage lasts until reaching a pressure less than 0.5 kbar. 151