Two-Dimensional C4N Global Minima: Unique Structural Topologies

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Two-Dimensional CN Global Minima: Unique Structural Topologies and Nano-electronic Properties Chunying Pu, DaWei Zhou, Yafei Li, Hanyu Liu, Zhongfang Chen, Yanchao Wang, and Yanming Ma J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b09960 • Publication Date (Web): 19 Jan 2017 Downloaded from http://pubs.acs.org on January 23, 2017

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The Journal of Physical Chemistry

Two-dimensional C4N Global Minima: Unique Structural Topologies and Nano-electronic Properties

Chunying Pua,b, Dawei Zhoub, Yafei Lic, Hanyu Liud, Zhongfang Chen*e, Yanchao Wang*a, and Yanming Maa a

State Key Lab of Superhard Materials, Jilin University, Changchun 130012, China College of Physics and Electronic Engineering, Nanyang Normal University, Nanyang 473061, China c College of Chemistry and Materials Science, Nanjing Normal University, Nanjing, Jingsu, 210023, China b

d

Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC

20015 e

Department of Chemistry, Institute for Functional Nanomaterials, University of Puerto Rico, Rio Piedras Campus, San Juan, Puerto Rico 00931

*

To whom correspondence should be addressed: [email protected](YW) and

[email protected] (ZC) 1

ACS Paragon Plus Environment


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Abstract Atomically thin two-dimensional (2D) materials have drawn great attention due to their many potential applications. We herein report two novel structures of 2D C4N identified by first-principles calculations in combination with a swarm structure search. These two structures (with symmetry of Pm and P2/m) are almost degenerate in energy (with only 4 meV/atom difference) and exhibit quite similar structural topologies, both consisting of alternative arrays of C-N hexagon and arrays of C-N pentagon-octagon-pentagon. The Pm structure is semiconducting with a direct band gap of 90 meV at HSE. In contrast, the P2/m structure is a zero-band-gap semimetal and possesses the distorted Dirac cone, showing the direction-dependent Fermi velocity and electronic properties. Thus, the predicted C4N monolayers are promising for applications in nano-electronics.

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Introduction Doping and alloying are efficient ways to modify the mechanical, electronic, optical, and other properties of materials. Since the preparation of graphene by Novoselov et al. in 2004,1 tremendous theoretical and experimental efforts have been devoted to doping and alloying graphene by other elements, such as boron (B), nitrogen (N), silicon (Si), and titanium (Ti).2-16 Particularly, two-dimensional (2D) carbon nitrides received great attention due to their many potential applications, such as semiconductor devices,17 high performance catalyst for energy conversion and storage,18,19 Li-ion batteries,20 and ultracapacitors.21 Substituting carbon atoms by nitrogen atoms at different configuration and concentration can alter the physical and chemical properties of graphene.22-27 Zhao et al.4 examined the individual N dopants in monolayer graphene grown on a copper foil substrate. Their joint experimental and theoretical studies revealed that the N atoms can substitute graphitic C atoms and a few lattice spacings of the N dopants can strongly modify the electronic structures of monolayer graphene. Lv et al.22 successfully

synthesized

N-doped

graphene

monosheets

containing

two

quasi-adjacent substitutional nitrogen atoms within the same graphene sub-lattice via atmospheric-pressure chemical vapor deposition, and revealed the presence of doping-induced localized states in the conduction band. By means of density functional theory (DFT) computations combined with the cluster-expansion and particle-swarm optimization method, Xiang et al.11 presented two ordered stable structures of N-doped graphene, namely C3N and C12N. These two monolayers are 3



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both semiconducting. Especially, C12N, with a direct band gap of 0.98 eV, might be a promising component for organic solar cells. Recently, Shi et al.23 investigated the limitations of N substitution in graphene by a constrained stable structure search, and found that the largest achievable N doping concentration is 33.3%−37.5%. Among the stable binary 2D alloys C1−xNx (x = 1/12, 1/8, 1/6, 1/4, 1/3), metallic behavior dominates, with the exception of the semiconducting structure at N concentration of 1/4. Furthermore, vacancies/holes can be involved in graphitic carbon nitrides, which greatly extend the graphitic carbon nitride family. g-C3N4 is the most eye-catching member due to its potential applications in fuel cells, photo-catalysis, and hydrogen production.24-26 Several structural isomers exist for g-C3N4, which can be categorized into two families based on their distinct heterocyclic building blocks: single-ring triazine or tri-ring heptazine, and they exhibit different electronic and magnetic properties, thus have different potential applications.27 Other graphitic carbon nitrides involving vacancies/holes have also been investigated. The DFT calculations by Du et al. 28 revealed that the C4N3 structure composed of single-ring triazines displays a ferromagnetic ground state and possesses an intrinsic half-metallicity. Thereafter, Wang and coworkers 29 pointed out that the C4N3 monolayer consisting of tri-ring heterocyclic units is energetically more favorable. Interestingly, by adding a small strain, this nonmagnetic monolayer can be converted into ferromagnetic, and the optical absorption can also be tuned. A recent exciting experimental achievement is that Mahmood et al.30 synthesized a new 2D crystal, C2N holey 2D (C2N-h2D) 4


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crystal, via a simple wet-chemical reaction. This material has an optical gap energy of about 2 eV, and the fabricated field-effect-transistor showed a high on/off ratio of 107, implicating its great potential for applications in electronics and optoelectronics. Moreover, the porous C2N monolayer could be an excellent candidate to separate He from natural gas.31 In fact, there are various ways to construct 2D C-N alloys, and many of their structures are still unknown. Note that the structure is the basis for the deep understanding of any physical and chemical properties. Therefore, the prediction of stable 2D C-N alloys is one of the keys to the discovery of new materials and properties. To further explore the new graphitic carbon nitride structures and their applications, we performed an unbiased global search on the stable structures of the 2D C4N compound. Two novel structures exhibiting quite similar structural topologies, namely, pentagonal-, hexagonal-, and octagonal-ring were identified. The band structure calculations indicate that these two structures are semiconductor with a narrow direct band gap (~ 90 meV) and zero-band-gap semimetal with the Dirac cone, respectively. Computational Methods In order to obtain the energetically most preferred structures of 2D C4N monolayers, we used the swarm-intelligence based PSO method 32 as implemented in the CALYPSO code. 33 34 The structures of 2D C4N were searched with simulation cell sizes with the total number of atoms no more than 20. The population size was set to be 30. At each step, only 60% of the structures were taken into the next generation 5



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evolution, while the others were randomly generated. The structural searching simulations for each calculation were stopped after generating 1500 structures (about 50 generations). Total energy calculations were performed in the framework of density functional theory within the generalized gradient approximation

35

as

implemented in the VASP code.36,37 The electron−ion interaction is described by pseudopotentials built within the projector augmented wave approximation 38 with 2s22p2 and 2s22p3 valence electrons for C and N atoms, respectively. A cutoff energy of 520 eV and 11×9×1 Monkhorst−Pack k-meshes were employed, and the total energy calculations were converged to less than 10-4 eV/atom. The 15 Å thickness vacuum region was adopted to ensure that interactions between the designed layer and its nearest-neighboring periodic images are negligible. The dynamic and thermal stabilities of the predicted structures were examined by phonon calculations and molecular dynamics simulations, respectively. The phonon calculations were performed with 120 atoms in 4×3 supercell by using the finite displacement approach as implemented in the Phonopy code. 39 The first principles molecular dynamics simulations adopting the constant temperature and volume (NVT) ensemble were performed with time steps of 2 fs for a total simulation time of about 10 ps at a temperature of 1500 K. Results and discussion First, we used CALYPSO method to search the lowest-energy structures of graphene and C2N monolayers. Our structure prediction method successfully reproduced the experimental graphene structure (2 atoms per cell) and nitrogenated 6


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holey 2D structure of C2N monolayer (with 18 atoms per unit cell) in the first and eighth generation, respectively. These results indicate that CALYPSO method is rather effective in locating the energetically most favorable structures of 2D materials. In order to obtain the energetically preferred structures of 2D C4N, we performed global minimum structure search of 2D C4N compound by CALYPSO method. The lowest-energy 2D C4N structures of Pm and P2/m are shown in Figure 1 (a) and (b), respectively. Despite the differences in symmetry, these two C4N monolayers exhibit quite similar structural topologies: they both contain C-N pentagonal-, hexagonal-, and octagonal-ring, the only difference is that the N atoms are at different locations. The total energy calculations reveal that the Pm structure is energetically favorable compared to the P2/m structure; however, the difference in the binding energy is very small (less than 4 meV/atom). Obviously, these two structures are almost degenerate in energy. Note that both of these structures consist of alternative arrays of C-N hexagons and arrays of C-N pentagon-octagon-pentagon, the quite similar C−N bonding patterns and structural topologies also account for their nearly degenerate energies. The C-C and C-N bond lengths are between single bonds and double bonds, indicating that the electrons are well delocalized in the rings.

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Figure 1. The predicted lowest-energy structures of 2D C4N with bond lengths for (a) Pm and (b) P2/m. Blue and brown spheres represent the nitrogen and carbon atoms, respectively.

To better understand the stabilities of these two structures, we employed the recently developed Solid State Adaptive Natural Density Partitioning (SSAdNDP) method 40 to analyze their chemical bonding. Based on the concept of the electron pair as the main element of chemical bonding models, SSAdNDP gives the patterns of chemical bonding in the periodic systems, and allows the interpretation of chemical bonding in terms of classical lone pairs and two-center bonds, as well as multi-center delocalized bonding. For both Pm and P2/m structures, each unit cell contains totally 42 electrons, including two lone pairs on two N atoms and 15 2c-2e σ bonds between C-C and C-N with occupation number 2.0 |e|, and eight multicenter π bonds, as revealed by the SSAdNDP analysis. For Pm structure, there are one 6c-2e π bond on the hexagon composed of six C atoms, one 4c-2e π bond on the four C atoms in the pentagon, and two 5c-2e π bonds on the five C atoms of hexagonal ring (Figure 2a). 8


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For P2/m structure, there are two 4c-2e π bonds on four C atoms in the pentagon and two 6c-2e π bonds on the hexagonal ring (Figure 2b). Clearly both systems have well delocalized π electrons, which explains their geometric characteristics (bond equalization) and high stabilities.

Figure 2. SSAdNDP chemical π bonding pattern of C4N monolayer for (a) Pm and (b) P2/m configurations. Blue and brown spheres represent the nitrogen and carbon atoms, respectively. To investigate thermodynamics stability, we have computed the formation energy of the known CxN1-x compounds to evaluate the experimental feasibility to obtain C4N. The formation energy 23 is defined as

E f (C x N1− x ) = Ecoh (C x N1− x ) − xµ C − (1 − x)µ N Here, Ecoh(CxN1−x) represents the cohesive energy of the CxN1−x compound (in eV per atom). The chemical potential of C and N (μC and μN) are taken from the cohesive energy of graphene and molecular N2, respectively. The calculated formation energy of both C4N structures is 0.97 eV, which is 0.02 and 0.01eV higher than the experimentally available C2N

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and C3N4 41 monolayers. Thus, we believe that it is 9



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rather feasible to synthesize C4N by the same or similar method used to synthesize C3N4 and C2N monolayers. Generally, the phonon calculation is a strict measure to check out dynamical stability of materials. To examine the dynamic stability of the predicted stable 2D structures, we have performed phonon calculations at 0K. As shown in Figure 3 (a) and (b), no imaginary phonon frequencies exist in the whole Brillouin zone, indicating the inherent dynamical stability of the Pm and P2/m phases for 2D C4N sheets.

Figure 3. Phonon dispersion and phonon density of states (DOS) of the 2D C4N structure for (a) Pm and (b) P2/m.

To further evaluate the stabilities, we performed first-principles molecular dynamics simulations at 1500 K on 2D C4N. Figure 4 (a) and (b) depict the fluctuations in the total energy and temperature as well as the snapshots of the geometries at the end of 10 ps simulations for Pm and P2/m phases, respectively. Notably the original planarity is well maintained at 1500 K after 10 ps simulation, only small structural fluctuations are observed, and the slightly distorted geometries can be relaxed back after full geometry optimization for both configurations. The 10


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well-preserved geometries at such a high temperature (1500K) indicate their remarkable thermal stabilities and possible applications at high temperature.

Figure 4. The temperature/energy fluctuations depend on simulated time in molecular dynamics simulations at 1500K, and the snapshots of C4N monolayer after a 10 ps MD simulation for (a) Pm and (b) P2/m structures. The gray balls and blue ones represent the C and N atoms, respectively.

Our above analyses showed that the Pm and P2/m structures are not only global minima of C4N monolayers, but also have outstanding dynamic and thermal stabilities, thus are highly feasible for experimental realization. Then, what will be their electronic properties? To address this question, we examined the energy band structures and density of states (DOSs) of these two planar C4N structures. Since GGA typically underestimates the band gaps, the screened hybrid functional of HSE42 was also used to calculate the band gaps. 11



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Since the valence band maximum (VBM) and the conduction band minimum (CBM) of both structures are not located at the high symmetry point or along the high symmetry point path, we adopted the dense Monkhorst-Pack 51×51×1 k-point meshes to calculate band gap values. The three-dimensional electronic band structures of Pm in the vicinity of the VBM and CBM were calculated by the PBE calculations and showed in Figure 5 (a). Note that the VBM and CBM are both located at the position (-0.1780, 0.4015, 0.0) in reciprocal space. In order to estimate the accurate band gap, the hybrid HSE calculations were performed to calculate the band structures and presented in Figure 5 (b). The Pm structure is semiconducting with a direct band gap of 90 meV at HSE (~ 30 meV at PBE). The partial charge densities of VBM and CBM for Pm are given in Figure 5 (c). It can be seen that the partial charge density of VBM and CBM features the character of π bond, which originates from pz orbitals. The three-dimensional electronic band structures of P2/m are showed in Figure 5 (d). It can be noted that two bands meet at position (0.50260, 0.17425, 0.0). It demonstrates that P2/m is a zero-band-gap semimetal and possesses the distorted Dirac cone. Furthermore, the band structures of P2/m were calculated by HSE hybrid functional and shown in Figure 5 (e). It can be seen that there is little change of band structures with hybrid functional calculations and it still shows semimetal character. It should be noted that the position of Dirac point in the P2/m structure is not located at the high symmetry point or along the high symmetry point path. The valence and the conduction bands in the vicinity of the Dirac points show the presence of distorted Dirac cones. Consequently, the Fermi velocity, which is defined as 12


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vF = (1 / h)(∂E / ∂k )E=EF (EF is the Fermi energy), is anisotropic. Around Dirac points, the valence and conduction bands exhibit a linear dispersion in the kx (Figure 5f) and ky directions (Figure 5g). By fitting these two bands, the corresponding minimum and maximum Fermi velocities are computed to be 5.70×105 and 8.40 ×105 m/s in the kx direction, respectively, whereas they are 7.59×105 and 1.05×106 m/s in the ky direction. Note that the maximum of Fermi velocity in the kx direction and ky direction is comparable to that of graphene (~8.22×105 m/s).43 The distortion of the Dirac cones appears not only in the 5-6-7 carbon rings,44 but also in our predicted C-N 5-6-8 rings, which means the direction-dependent electronic properties, especially conductivities. To gain deep insight into the electronic structures, we also plotted total density of states and orbital-projected atomic density of states (DOSs) of Pm and P2/m structures in Figure 6 (a) and (b), respectively. The VBM and the CBM in both structures are mainly contributed by the 2pz orbitals of C and N atoms, which is consistent with the partial charge densities profiles for Pm structure.

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Figure 5. The three-dimensional band structures in the vicinity of the VBM and CBM for (a) Pm and (d) P2/m structures. The HSE band structures of (b) Pm and (e) P2/m structures. The partial charge densities of VBM and CBM for (c) Pm and the bands around the Dirac points in kx (f) and ky (g) directions are enlarged for P2/m structure. The Fermi level is at 0 eV.

Figure 6. The total and orbital-projected atomic density of states for (a) Pm and (b) 14


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P2/m structures. Conclusions In summary, using an unbiased structure-search method based on particle-swarm optimization algorithms in combination with DFT calculations, we performed extensive structure searches on the 2D C4N compound. Two novel structures (Pm and P2/m) with similar structural features were identified to be nearly degenerate in energy (with only 4 meV/atom difference) and have outstanding dynamic and thermal stabilities. Our electronic calculations indicate that the Pm structure is semiconducting with a direct band gap of 90 meV, while the P2/m structure is a gapless semi-metal with distorted Dirac cone. All these analyses indicate that the predicted C4N monolayers are experimentally feasible C-N material with narrower band gap or distorted Dirac cones, which holds considerable promise for applications in nano-electronics. Acknowledgement This work is supported in China by the National Natural Science Foundation of China (Grant Nos. 11404128, U1304612, U1404608, 11274136, and 11534003), the National Key Research and Development Program of China under Grants No. 2016YFB0201200, the Postdoctoral Science Foundation of China (Grant Nos. 2015M581766, 2014M551181 and 2015T80294), Young Core Instructor Foundation of Henan Province (No. 2015GGJS-122), Science Technology Innovation Talents in Universities of Henan Province (No.16HASTIT047), and in USA by Department of Defense (Grant W911NF-12-1-0083). Parts of the calculations were performed at the 15



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High-Performance Computing Center of Jilin University and Tianhe2-JK in the Beijing Computational Science Research Center. Work at Carnegie was supported by EFree, an Energy Frontier Research Center funded by the DOE, Office of Science, Basic Energy Sciences under Award No. DE-SC-0001057. Supporting Information The coordinates of the two lowest-energy structures (Pm and P2/m), the optimized geometries of six low-energy structures of 2D C4N, and the energy band structures of C4N with different values of biaxial strain in the two lowest energy structures. This material is available free of charge via the Internet at http://pubs.acs.org. References (1) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666-669. (2) Wu, X.; Pei, Y.; Zeng, X. C. B2C Graphene, Nanotubes, and Nanoribbons. Nano Lett. 2009, 9, 1577-1582. (3) Luo, X.; Yang, J.; Liu, H.; Wu, X.; Wang, Y.; Ma, Y.; Wei, S. H.; Gong, X.; Xiang, H. Predicting Two-Dimensional Boron-Carbon Compounds by the Global Optimization Method. J. Am. Chem. Soc. 2011, 133, 16285-16290. (4) Zhao, L.; He, R.; Rim, K. T.; Schiros, T.; Kim, K. S.; Zhou, H. Visualizing Individual Nitrogen Dopants in Monolayer Graphene. Science 2011, 333, 999-1003. (5) Yanagisawa, H.; Tanaka, T.; Ishida, Y.; Matsue, M.; Rokuta, E.; Otani, S.; Oshima, C. Phonon Dispersion Curves of a BC3 Honeycomb Epitaxial Sheet. Phys. Rev. Lett. 2004, 93, 177003. 16


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6) Tanaka, H.; Kawamata, Y.; Simizu, H.; Fujita, T.; Yanagisawa, H.; Otani, S.; Oshima, C. Novel Macroscopic BC3 Honeycomb Sheet. Solid State Commun. 2005, 136, 22-25. (7) Lin, S. S. Light-Emitting Two-Dimensional Ultrathin Silicon Carbide. J. Phys. Chem. C 2012, 116, 3951-3955. (8) Zhou, L. J.; Zhang, Y. F.; Wu, L. M. SiC2 Siligraphene and Nanotubes: Novel Donor Materials in Excitonic Solar Cells. Nano Lett. 2013, 13, 5431-5436. (9) Ding, Y.; Wang, Y. Geometric and Electronic Structures of Two-Dimensional SiC3 compound. J.Phys. Chem. C 2014, 118, 4509-4515. (10) Liu, J.; He, C. Y.; Jiao, N.; Xiao, H. P.; Zhang, K. W.; Wang, R. Z.; Sun, L. Z. Novel Two-Dimensional SiC2 Sheet with Full Pentagon Network. 2013, arXiv:1307, 6324. (11) Xiang, H. J.; Huang, B.; Li, Z. Y.; Wei, S. H.; Yang, J. L.; Gong, X. G. Ordered Semiconducting Nitrogen-Graphene Alloys. Phys. Rev. X 2012, 2, 011003. (12) Cahangirov, S.; Topsakal, M.; Akturk, E.; Sahin, H.; Ciraci, S. Two- and One-Dimensional Honeycomb Structures of Silicon and Germanium. Phys. Rev. Lett. 2009, 102, 236804. (13) Padova, P. D.; Quaresima, C.; Ottaviani, C.; Sheverdyaeva, P. M.; Moras, P.; Carbone, C.; Topwal, D.; Olivieri, B.; Kara, A.; Oughaddou. H. et al. Evidence of Graphene-Like Electronic Signature in Silicene Nanoribbons. Appl. Phys. Lett. 2010, 96, 261905. (14) Aufray, B.; Kara, A.; Vizzini, S. b.; Oughaddou, H.; Léandri, C.; Ealet, B.; Le 17



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Lay, G. Graphene-Like Silicon Nanoribbons on Ag(110): A Possible Formation of Silicene. Appl. Phys. Lett. 2010, 96, 183102. (15) Zhang, Z.; Liu, X.; Yakobson, B. I.; Guo, W. Two-Dimensional Tetragonal TiC Monolayer Sheet and Nanoribbons. J. Am. Chem. Soc. 2012, 134, 19326-19329. (16) Zhao, T.; Zhang, S.; Guo, Y.; Wang, Q. TiC2: A New Two-Dimensional Sheet Beyond Mxenes. Nanoscale 2016, 8, 233-242. (17) Wang, X.; Li, X.; Zhang, L.; Yoon, Y.; Weber, P. K.; Wang, H.; Guo, J.; Dai, H. N-Doping of Graphene through Electrothermal Reactions with Ammonia. Science 2009, 324, 768-771. (18) Cui, T.; Lv, R.; Huang, Z.-H.; Zhu, H.; Zhang, J.; Li, Z.; Jia, Y.; Kang, F.; Wang, K.; Wu, D. Synthesis of Nitrogen-Doped Carbon Thin Films and Their Applications in Solar Cells, Carbon 2011, 49, 5022-5028. (19) Qu, L.; Liu, Y.; Baek, J. B.; Dai, L. Nitrogen-Doped Graphene as Efficient Metal-Free Electrocatalyst for Oxygen Reduction in Fuel Cells, ACS Nano 2010, 4, 1321-1326. (20) Reddy, A. L. M.; Srivastava, A.; Gowda, S. R.; Gullapalli, H.; Dubey, M.; Ajayan, P. M. Synthesis of Nitrogen-Doped Graphene Films for Lithium Battery Application. ACS Nano 2010, 4, 6337-6342. (21)Jeong, H. M.; Lee, J. W.; Shin, W. H.; Choi, Y. J.; Shin, H. J.; Kang, J. K.; Choi, J. W. Nitrogen-Doped Graphene for High-Performance Ultracapacitors and the Importance of Nitrogen-Doped Sites at Basal Planes. Nano Lett. 2011, 11, 2472-2477. (22) Lv, R., Li, Q.; Botello-Méndez, A.R.; Hayashi, T.; Wang, B.; Berkdemir, A.; Hao, 18


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Q.; Elías, A.L.; Cruz-Silva, R.; Gutiérrez, H.R. et al. Nitrogen-Doped Graphene: Beyond Single Substitution and Enhanced Molecular Sensing. Sci Rep 2012, 2, 586. (23)Shi, Z.; Kutana, A.; Yakobson, B. I. How Much N-Doping Can Graphene Sustain? J. Phys. Chem. Lett. 2015, 6, 106-112. (24) Xiang, Q.; Yu, J.; Jaroniec, M. Preparation and Enhanced Visible-Light Photocatalytic H2-Production Activity of Graphene/C3N4 composites. J. Phys. Chem. C 2011, 115, 7355-7363. (25) Sehnert, J.; Baerwinkel, K.; Senker, J. Ab Initio Calculation of Solid-State NMR Spectra for Different Triazine and Heptazine Based Structure Proposals of g-C3N4. J. Phys. Chem. B 2007, 111, 10671-10680. (26) Wang, Y.; Wang, X.; Antonietti, M. Polymeric Graphitic Carbon Nitride as a Heterogeneous Organocatalyst: From Photochemistry to Multipurpose Catalysis to Sustainable Chemistry. Angew Chem Int Ed Engl 2012, 51, 68-89. (27) Xu, Y.; Gao, S.-P. Band Gap of C3N4 in the GW Approximation. Int. J. Hydrogen Energy 2012, 37, 11072-11080. (28) Du, A.; Sanvito, S.; Smith, S. C. First-Principles Prediction of Metal-Free Magnetism and Intrinsic Half-Metallicity in Graphitic Carbon Nitride. Phys. Rev. Lett. 2012, 108, 197207. (29) Li, X.; Zhang, S.; Wang, Q. Stability and Physical Properties of a Tri-Ring Based Porous g-C4N3 Sheet. Phys. Chem. Chem. Phys. 2013, 15, 7142-7146. (30) Mahmood, J.; Lee, E. K.; Jung, M.; Shin, D.; Jeon, I. Y.; Jung, S. M.; Choi, H.J.; Seo, E. K.; Bae, S.Y.; Sohn, S. D. et al. Nitrogenated Holey Two-Dimensional 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Structures. Nat. Commun. 2015, 6, 6486. (31) Zhu, L.; Xue, Q.; Li, X.; Wu, T.; Jin, Y.; Xing, W. C2N: An Excellent Two-Dimensional Monolayer Membrane for He Separation. J. Mater. Chem. A 2015, 3, 21351-21356. (32) Wang, Y.; Miao, M.; Lv, J.; Zhu, L.; Yin, K.; Liu, H.; Ma, Y. An Effective Structure Prediction Method for Layered Materials Based on 2D Particle Swarm Optimization Algorithm. J. Chem. Phys. 2012, 137, 224108. (33) Wang, Y.; Lv, J.; Zhu, L.; Ma, Y. Crystal Structure Prediction Via Particle-Swarm Optimization. Phys. Rev. B 2010, 82, 094116. (34) Wang, Y.; Lv, J.; Zhu, L.; Ma, Y. Calypso: A Method for Crystal Structure Prediction. Comput. Phys. Commun. 2012, 183, 2063-2070. (35) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865. (36) Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6, 15-50. (37) Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev. B 1999, 59, 1758-1775. (38) Blochl, P. E. Projector Augmented-Wave Method. Phys. Rev. B 1994, 50, 17953-17979. (39) Togo, A.; Oba, F.; Tanaka, I. First-Principles Calculations of the Ferroelastic Transition between Rutile-Type And CaCl2-Type SiO2 at High Pressures. Phys. Rev. B 20


Page 20 of 21

Page 21 of 21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2008, 78, 134106. (40) Galeev, T. R.; Dunnington, B. D.; Schmidt, J. R.; Boldyrev, A. I. Solid State Adaptive Natural Density Partitioning: A Tool for Deciphering Multi-Center Bonding in Periodic Systems. Phys. Chem. Chem. Phys. 2013, 15, 5022-5029. (41) Wang, X; Maeda, K; Thomas, A; Takanabe,K; Xin,g; M.Carlsson, J; Domen, K; Antonietti, M. A metal-free Polymeric Photocatalyst for Hydrogen Production from Water under Visible light. Nature Mater. 2008, 10, 1038. (42) Heyd, J.; Scuseria, G. E.; Ernzerhof, M. Hybrid Functionals Based on a Screened Coulomb Potential. J. Chem. Phys. 2003, 118, 8207-8215. (43) Nulakani, N. V. R.; Subramanian, V. A Theoretial Study on the Design, Structure, and Electronic Properties of Novel Forms of Graphynes. J. Phys. Chem. C 2016, 120, 15153-15161. (44)Wang, Z.; Zhou, X; Zhang, X; Zhu, Q; Dong, H; Zhao, M; Oganov, A. R. Phagraphene: A Low-Energy Graphene Allotrope Composed of 5-6-7 Carbon Rings with Distorted Diran Cones. Nano Lett. 2015,15, 6182-6186.

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Two-Dimensional C4N Global Minima: Unique Structural Topologies

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