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Quantum Chemistry of Nanotubes Electronic Cylindrical Waves Pavel N. D’yachkov Quantum Chemistry Laboratory Kurnakov Institute of General and Inorganic Chemistry Russian Academy of Sciences Moscow, Russia p, A SCIENCE PUBLISHERS BOOK Cover Illustrations The cattle figure was sourced from the editor’s personal figures collection. Reproduced with the permission of the editor, Prof. R.A. Hill. Cover illustration reproduced from ‘Electronic Structure of Carbon Nanotubes with Copper Core’ by The lower five panels are from: I.A. Bochkov and P.N. D’yachkov in the “Russian Journal of Inorganic Chemistry”, Jan. 2013, Springer Acharya, S. and Hill, R.A. (2014). High efficacy gold-KDEL peptide-siRNA nanoconstruct-mediated transfection iNCCnRR aCtCCu 2 PrPCerre.1e sR2ss sempryoodbulacsetds bayn dp emrmyoistusiboens.. Nanomedicine: Nanotechnology, Biology and Medicine. 10:329-337. 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Names: Liu, Jian (Chemical engineer), editor. | Jiang, San Ping, editor. Library of Congress Cataloging‑in‑Publication Data Title: Mesoporous materials for advanced energy storage and conversion tNecahmneoslo: gJaiens i/â ced, MitoirlLsa,i nbJi,ra aanur Lyt hiouof, rCD.oepnagrrtemsse nCta otfa Clohgeimngi‑cianl ‑EPnugbinlieceartiinogn, Data Faculty of Science and Engineering, Curtin University, Perth, WA, NATNuaiatmslmtere:aes Tls: i:Lar Sa,i ucSn,aa sJnnpiae oPnsri, n (tCC gsL. hy JGieisabmt.ne,r igemac,d arFsilyt ue:o eonmrl.fgs |o iCa nHdnoeedienll rllEg,)i ,nnR reeegodrs,dgi stpnyo lC eraT.yn ae| Act nJahii.a,lnn noeogggdl o,aii tSgnnoaydgrn .I- e niPnvsitan-iPltguu,u ateebtd il&oiitncoar /.t Mionil aDna Jtaaniâc, TDDTieeitptlpleae:ar :M rtBmtmeioesloneopntg ooty rfo ooCfuf hT sde rmomamanitceseapsrltio iaEcrln stag fn&ionir mPe aeladarlvisnna n/gn ei,c nCdegidut, or eFtrniasne,c r CUugylont lisyivtn eoo rrGfsa Ci.gt Syeiv, c aPianlen dEre tncsho,g, UniWnvneeAirev,sreiiornsnigt ya onfd tAGWeuceshiostncrsNoacollianoieamsgn.iincee,ess Ds:/ D &eepd' yDaitaroectrmphsa,ke rJonitavtmn o, eLfP niB.u tNi ,oo D.lf o( eAPgpiaiacrvra teTlm lSr Neacninietksn opocfloe aCr,e tMhv aeiimnclwhdic) aO,au alk puEeetnerhg,a oiWtnrieo.Ien, rUsin,S FgA,a,c Ruoltdyn oefy A. 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Werner Heisenberg Preface Quantum chemistry is the quantum mechanics of atoms, molecules, and solids. Until recently, the quantum chemistry of crystals was regarded as part of a solid-state physics and was a theoretical foundation of materials sciences. Now in the time of nanotechnology, when individual molecules have become the building block of electronic devices, molecular quantum chemistry has become an important part of materials science. Nanotubes lie halfway from the molecules to crystals and they are at a center progress in nanoelectronics. Quantum chemistry of nanotubes is being developed by the efforts of the molecular and solid-state theorists. At first, the electronic structure of carbon nanotubes was described using the simplest quantum chemical Hückel molecular orbital theory elaborated for π-conjugated organic compounds. The qualitatively correct predictions obtained of the relationships between the geometry and band structure of carbon nanotubes engendered a large number of experimental studies of their electronic properties and design of nanoelectronics elements. There was a need for more accurate calculations of nanotubes, and an alternative and somewhat theoretically more substantiated and detailed description of the nanotubes electron states came from the solid-state quantum chemistry when Slater’s augmented plane wave method was taken as a starting point for tubules studies. However, the cylindrical (tubular) geometry of nanotubes determines the formation of cylindrical electron waves in tubules, rather than plane waves as in crystals. This book provides a detailed exposition of nonrelativistic and relativistic linearized augmented cylindrical wave technique and demonstrates its applications to the various carbon and non-carbon, achiral and chiral, pure, intercalated and doped single-walled, double-walled, and embedded nanotubes and iv Quantum Chemistry of Nanotubes nanowires. We hope to convince the reader that the use of cylindrical waves for nanotubes offers a great advantages in the studies of their properties. Pavel N. D’yachkov Contents Preface iii Introduction vii 1. Augmented Cylindrical Waves for Nonchiral Nanotubes and Wires 1 1.1. Geometry of Carbon Nanotubes 1 1.2. Theory 2 1.3. Applications 20 2. Augmented Cylindrical Waves for Embedded and Double-Walled Nanotubes 62 2.1. Embedded Nanotubes 62 2.2. Double-Walled Carbon Nanotubes 72 3. Symmetrized Augmented Cylindrical Waves for Chiral Nanotubes 91 3.1. Theory 93 3.2. Applications 103 4. Augmented Cylindrical Wave Green’s Function Technique for Impurities 124 4.1. Defects in Nanotubes 124 4.2. Theory 128 4.3. Applications 138 vi Quantum Chemistry of Nanotubes 5. Relativistic Augmented Cylindrical Wave Method 151 5.1. Spin-Orbit Interaction in Nanotubes 151 5.2. Theory 153 5.3. Applications 154 Appendix: Darwin and Mass-velocity Corrections 186 References 190 Index 210 Introduction Nanotubes are the nanometer-scale chemical compounds with cylindrical geometry (Iijima 1991). All the single-walled carbon nanotubes can be constructed by rolling up a single graphite sheet, and the structures of tubules can be labeled by the pair of integers n and n (where n ≥ n ≥ 0), 1 2 1 2 which, together with C-C bond length d = 1.42 Å determine a geometry C-C of the tubule. They are currently the focus of intense multidisciplinary studies because of their unique physical and chemical properties and their prospects for practical applications in molecular electronics (Saito et al. 1998, De Volder et al. 2013, Laird et al. 2015, Dekker 2018, Peng 2018, Bai et al. 2018, He et al. 2018, Gupta et al. 2018, Cao et al. 2017) that is perhaps the most intriguing area of nanotechnology. Chemically, the carbon nanotubes are the aromatic conjugated compounds. The theoretical simulation of the nanotubes electronic structure have received much attention since 1992, when the first calculations for the band structures of all-carbon nanotubes were done using the Linear Combination of Atomic Orbitals (LCAO) and π-electron tight-binding techniques (Mintmire et al. 1992, Saito et al. 1992a, Saito et al. 1992b, Hamada et al. 1992, White et al. 1993). Particularly, it was shown that the electronic structure of any tubule in a region of the occupied and unoccupied π states can be obtained within the tight-binding model by folding the graphene π bands along a certain direction in the two-dimensional Brillouin zone. The zone-folding technique has proven immensely successful in providing physically relevant information on the nature of electronic interactions in nanotubes. In this approach, it was predicted that a nanotube is a metal if n − n is a multiple of 3, or a semiconductor otherwise. 1 2 Later on, the modified tight-binding π electron and all-valence orbital band structure models were developed that account for the effects of the sπ-hybridization, misalignment of carbon p -orbitals on the curved π graphene surface, chirality, and diameter dependence of nearest-neighbor viii Quantum Chemistry of Nanotubes hopping integral (Saito et al. 2001, Mintmire et al. 1993, Mintmire and White 1998, Rubio et al. 1999, Hagen and Hertel 2003, Vadapalli and Mintmire 2006, Bulusheva et al. 1998, Bussi et al. 2005). This leads particularly to modifications of the gap energies, which reveals that the single-walled carbon nanotubes with n − n = 3n (n = 1,2,…) can be very-small-gap 1 2 semiconductors, and that these effects are of great importance in the case of the small- and moderate radius nanotubes. These include terms causing the trigonal warping effects, similar to the zone folding technique results for the highest occupied and lowest unoccupied π states of the single-walled carbon nanotubes that were obtained using an effective-mass k·p approximation (Ajiki and Ando 1993, 1996). Going beyond the semi empirical tight-binding methods or k·p approximation, one can perform the first-principles calculations for actual curved-surfaced tubule. A version of LCAO pseudopotential method, in which the core electrons are replaced by the nonlocal norm-conserving pseudopotentials and the valence electrons are treated using a linear combination of multiple-ζ and polarized atomic orbitals, was applied in the calculation of the electronic dispersion energies and density of states in the Fermi energy region for several small tubules (Christ and Sadeghpour 2007, Reich et al. 2002). In the Fermi energy region, the electronic structure of nanotubes was also studied using the plane-wave basic and ab initio pseudopotential Local-Density-Functional theory (DFT) (Blasé et al. 1994, Charlier et al. 1996 a,b, Machón et al. 2002, Marinopoulos et al. 2003, Zólyomi and Kürti 2004, Cabria et al. 2003, Dubay et al. 2002, Li et al. 2001, Liu and Chan 2002, Kürti et al. 2004, Miyake and Saito 2005). One assumes that predictive power and accuracy of the tight-binding calculations are less robust compared with the ab initio DFT methods (Christ and Sadeghpour 2007). Using this ab initio method, it was possible to study in more detail the curvature-induced π- and s-band mixing and the deviations of chemical bonding from the sp2 hybridization. In particular, these effects were found to significantly alter the electronic structure of narrow nanotubes compared to the predictions of the tight- binding model. In the case of small-diameter insulating nanotubes, where the diameter is less than 1 nm, the strong π-s rehybridization modifies the low-lying nondegenerate conduction band states (Marinopoulos et al. 2003, Zólyomi and Kürti 2004). The pseudopotential calculations on the narrow tubes such as (5, 0) revealed total closure of the gap. Since the 90s, we are developing a Linearized Augmented Cylindrical Wave (LACW) method for the nanotubes band structure (D’yachkov et al. 1998, D’yachkov et al. 1999, D’yachkov and Kirin 1999). The LACW method is an extension of the one-dimensional multiatomic systems with tubular structure of the Augmented Plane Wave (APW) theory suggested for the bulk materials (Slater 1937, Slater 1974) and developed the latter Introduction ix in a form of more efficient linearized APW (LAPW) technique (Andersen 1975, Koelling and Arbman 1975). During the past decades, the techniques for APW and LAPW calculations have reached the point at which, with the aid of large computers, a solution of the band structure problem may be obtained for particular crystals, including those with heavy metals (Singh 1994, Singh and Nordstrom 2006). There is good reason to believe that the LAPW method is one of the most accurate computational schemes in the bulk solid-state electronic structure theory. These developments have challenged an extension of the LAPW approach to low-dimensional systems such as nanofilms (Jepsen et al. 1978, Krakauer et al. 1979), nanotubes and nanowires (D’yachkov 1997, 2004, 2016, Mokrousov et al. 2005, 2006) and fullerene-type spherical clusters (D’yachkov and Kuznetsov 2004). The LACW method, as applied to the nanotubes, has an advantage over the conventional LCAO and plane-wave pseudopotential methods. While low level LCAO calculations are relatively easy to do, improving the accuracy quickly becomes both technically demanding and computationally very expensive. The main concern with approaches of the LCAO method is the transferability of the basic set. Moreover, it is well known from the band structure of bulk materials that the LCAO basis is adequate to achieve good results for the valence band, but sometimes not for the conduction band, because this basis does not include the delocalized conducting plane-wave-type functions. The plane-wave pseudopotential calculations suffer from a slow convergence and an unfavorable scaling: The number of basic functions and the time taken to perform such a calculation on a computer increase asymptotically with the cube of the number of atoms (Skylaris et al. 2005). This method is computationally quite cumbersome for calculating the band structure of the chiral tubes without rotational symmetry and very large translational unit cells; hence, the availability of such results in the literature is very limited. The purely delocalized nature of the plane-wave basic set puts obstacles in the way of calculating the inner low-energy states of the valence band, e.g., the carbon nanotubes p and s bands. The basis of the LACW method has s both localized and delocalized components. Finally, the main argument for using cylindrical waves is to account for the cylindrical geometry of the nanotubes in an explicit form that offers the obvious advantages. The purpose of this book is two-fold. First of all, it provides the physical basis and gives the detailed exposition of the LACW method, so that newcomers to nanomaterial’s studies can quickly learn the technique, and if desired construct a working code. Connections are made between the standard LAPW method for solids and the LACW for nanotubes that must make the LACW approach more understandable for the readers experienced in the solid-state LAPW methods. The experimental detection of spin-orbit gaps in the carbon nanotubes stimulated an interest to the

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