A method and device for evaluating the influence of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first principles

Abstract

The application discloses a method and equipment for evaluating influence of chirality and pipe diameter on structure and property of single-walled carbon nanotubes based on first principle, and belongs to the cross technical field of computational material science and nanometer material simulation and performance prediction. The application firstly constructs initial crystal models of single-walled carbon nanotubes with similar pipe diameters and different chirality structures, and carries out K-point convergence test; takes the optimal K-point grid density as a calculation parameter, and takes fine precision as a convergence judgment basis to carry out geometric optimization on the initial crystal models, and carries out electronic structure calculation on the stable crystal models; then constructs initial crystal models of single-walled carbon nanotubes with the same chirality and different pipe diameters, and carries out Ecut cut-off energy and K-point convergence test; takes the optimal K-point grid and the converged plane wave cut-off energy as a convergence judgment basis to carry out geometric optimization on the initial crystal models, and carries out electronic structure calculation and mechanical performance calculation on the stable crystal models. The application provides a theoretical basis for high-performance application of single chirality carbon nanotubes.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of computational materials science and nanomaterial simulation and performance prediction, specifically relating to a method and apparatus for evaluating the influence of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations. Background Technology

[0002] Single-walled carbon nanotubes, as typical one-dimensional nanomaterials, have attracted much attention since their discovery due to their extraordinary electronic structure and mechanical properties. Their applications are very broad, such as in infrared detection; based on the Stefan-Boltzmann law: Any object with a temperature above thermodynamic zero radiates energy, which can be detected by infrared detection devices. This is the core theoretical basis of infrared detection and stealth technology. Based on this principle, the infrared radiation intensity of a target is positively correlated with its infrared emissivity ε and the fourth power of its surface temperature T. Therefore, reducing the infrared emissivity or surface temperature of a target surface has become a key approach to achieving infrared stealth. Through further research, researchers have discovered a direct relationship between the emissivity ε in the mid- and far-infrared regions and the resistivity ρ of the material. Generally speaking, the lower the resistivity of a material, the lower its emissivity; that is, the higher the conductivity, the lower the emissivity. Different chiral structures or tube diameters all affect the structure and properties of single-walled nanotubes. In practical applications, the selection of single-walled carbon nanotubes needs to be based on the application requirements. For example, in the infrared detection field mentioned above, highly conductive single-walled carbon nanotubes are required to achieve high responsivity, fast response speed, low dark current / noise, and stable photoelectric conversion performance in infrared detectors. Therefore, the analysis of the structure and properties of different single-walled carbon nanotubes is very important.

[0003] However, the single-walled carbon nanotubes currently prepared and used are usually mixtures of various chiral structures. This inherent chiral structure mixture limits the application of single-walled carbon nanotubes to a certain extent, including high-performance applications, poor uniformity of device performance, and inconsistent interfacial bonding strength, which in turn affects the stability of composite materials. Summary of the Invention

[0004] The purpose of this invention is to use density functional theory as a calculation method to simulate and analyze the unit cells of single-walled carbon nanotubes with single chirality and fixed diameter. This allows for a clearer deduction of the specific ways in which chirality and diameter affect the intrinsic structure, enabling effective prediction of their performance, selecting single-walled carbon nanotubes that are more suitable for the field of infrared stealth, and providing key theoretical support for the future development of high-performance applications of single-type carbon nanotubes.

[0005] This invention provides a method for evaluating the effects of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations, comprising the following steps:

[0006] Step 1: Construct initial crystal models of single-walled carbon nanotubes with similar diameters but different chiral structures;

[0007] Step 2: Based on the initial crystal model in Step 1, conduct a K-point convergence test to determine the optimal K-point grid density; based on the optimal K-point grid density determined by the convergence test, use the fine precision as the convergence criterion to perform geometric optimization on the initial crystal model to obtain a stable crystal model.

[0008] Step 3: Perform electronic structure calculations on the stable crystal model described in Step 2 to complete the analysis of the influence of chirality on the structure and properties of single-walled carbon nanotubes;

[0009] Step 4: Construct initial crystal models of single-walled carbon nanotubes with the same chiral structure but different diameters;

[0010] Step 5: Based on the initial crystal model in Step 4, conduct Ecut cutoff energy and K-point convergence tests to determine the optimal K-point grid density and convergent plane wave cutoff energy; based on the optimal K-point grid density and convergent plane wave cutoff energy determined by the convergence test, perform geometric optimization on the initial crystal model with fine precision as the convergence criterion to obtain a stable crystal model.

[0011] Step 6: Perform electronic structure and mechanical property calculations on the stable crystal model described in Step 5 to complete the analysis of the influence of tube diameter on the structure and properties of single-walled carbon nanotubes.

[0012] Furthermore, in step 1, after the initial crystal model is constructed, the thickness of the vacuum layer is increased by 15~25 Å in the direction perpendicular to the axis of the single-walled carbon nanotube.

[0013] Furthermore, in step 1, among single-walled carbon nanotubes with similar diameters but different chiral structures, the diameter error is less than 0.5 Å.

[0014] Furthermore, in step 2, the K-point convergence test is performed using the Dmol3 module, adjusting only the K-point density. The Monkhorst-Pack grid is selected as the K-point sampling method, and different K-point grid densities are set. The grid density is 1*1*n in one direction. The optimal K-point grid density is determined based on the total energy difference between two adjacent calculations being less than 0.01eV.

[0015] Furthermore, in step 2, the initial crystal model is geometrically optimized using the DMol3 module. During the geometric optimization process, the GGA-PBE exchange-correlated functional and the dual numerical polarization basis set DNP are used for all-electronic structure calculations, and the self-consistent convergence criterion for geometric optimization is 1×10⁻⁶. -6 .

[0016] Furthermore, in step 3, the electronic structure calculation selects the Γ-A path along the tube axis in the Brillouin zone as a representative path, and calculates the band structure, density of states, and partial density of states along the path.

[0017] Furthermore, in step 4, after the initial crystal model is constructed, the thickness of the vacuum layer is increased by 15~25 Å in the direction perpendicular to the axis of the single-walled carbon nanotube.

[0018] Further, in step 5, the cutoff energy and K-point convergence test are performed using the Castep module. When testing the cutoff energy, a K-point grid density of 1*1*n is selected, other parameters are fixed, and the corresponding energies under different cutoff energies are tested respectively. The cutoff energy corresponding to the lowest energy point is selected. Then, the K-point grid density is tested. The cutoff energy is selected, other parameters are fixed, and the energy under different K-point grid densities in a single direction of 1*1*n is tested respectively. The K-point grid density corresponding to the lowest energy point is selected. Based on the total energy difference between two adjacent calculations being less than 0.01eV, the optimal K-point grid density and convergent plane wave cutoff energy are determined.

[0019] Furthermore, the initial crystal model is geometrically optimized using the Castep module. During the geometric optimization process, the GGA-PBE exchange-correlated functional is used, combined with the TPSD structure optimization algorithm and the dual numerical polarization basis set DNP for all-electronic structure calculation. The self-consistent convergence criterion for geometric optimization is 10. -6 .

[0020] Furthermore, in step 6, the electronic structure calculation selects the Γ-A path along the tube axis in the Brillouin zone as a representative path to calculate the band structure and density of states along the path; the mechanical property calculation uses the Castep module, including Young's modulus, shear modulus, bulk modulus and fracture toughness.

[0021] The present invention also provides a computer device / apparatus / system, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method described above for evaluating the effect of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations.

[0022] The present invention also provides a computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a processor, implements the steps of the method described above for evaluating the effect of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations.

[0023] The present invention also provides a computer program product, including a computer program / instructions that, when executed by a processor, implement the steps of the method described above for evaluating the effect of chirality and diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations.

[0024] The beneficial effects of this invention are as follows:

[0025] The band structure analysis method involved in this invention can help researchers understand the energy level distribution of electrons inside nanotubes. By unfolding and calculating the band structure of the material, relevant information on the change of electronic energy levels with momentum (i.e., wave vector) can be obtained. This information plays a key role in understanding the electrical conductivity and electronic transport properties of the material, and simultaneously correlates the electronic structure with mechanical properties, providing multi-dimensional theoretical support for the practical application of the material.

[0026] Furthermore, band structure data can be used to predict the electronic band gap (the energy difference between the conduction band and the valence band) of materials, and the electronic band gap parameter is crucial for the research and application of the photoelectric properties of materials. Simultaneously, electronic structure calculations can further reveal core information such as the wave function and charge density of electrons within the material. This information will provide strong support for in-depth research into the distribution and interaction mechanisms of electrons within the material, and will provide a theoretical foundation for the high-performance applications of single chiral carbon nanotubes. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating the first-principles calculation method of the present invention.

[0028] Figure 2 Schematic diagram of the chiral single-walled carbon nanotube models with similar diameters but different chiralities used in this invention: (a)(6,6) armchair-shaped carbon nanotube, (b)(10,0) serrated carbon nanotube, (c)(8,4) chiral carbon nanotube, (d)(4,8) chiral carbon nanotube.

[0029] Figure 3 A schematic diagram of the selection of Brillouin zone path in the electronic structure calculation process of single-walled carbon nanotubes: (a) Brillouin zone path of hexagonal crystal system, (b) Brillouin zone path adopted for the properties of one-dimensional carbon nanotubes.

[0030] Figure 4The following diagrams show the band structures of carbon nanotubes with different chiralities: (a)(6,6) armchair-shaped carbon nanotube band structure, (b)(10,0) serrated carbon nanotube band structure, (c)(8,4) chiral carbon nanotube band structure, and (b)(4,8) chiral carbon nanotube band structure.

[0031] Figure 5 The density of states (DOS) plots for (a) (6,6) armchair-shaped carbon nanotubes and (b) (10,0) zigzag-shaped carbon nanotubes are shown.

[0032] Figure 6 The density of states (DOS) plots are for different chiral carbon nanotubes; where (a) is the DOS plot for chiral carbon nanotubes with a density of states of (8,4) and (b) is the DOS plot for chiral carbon nanotubes with a density of states of (4,8).

[0033] Figure 7 The partial density of states (PDOS) plots are for different chiral carbon nanotubes; (a) (6,6) partial density of states (PDOS) plot for armchair-shaped carbon nanotubes, (b) (10,0) partial density of states (PDOS) plot for serrated carbon nanotubes, (c) (8,4) partial density of states (PDOS) plot for chiral carbon nanotubes, and (d) (4,8) partial density of states (PDOS) plot for chiral carbon nanotubes.

[0034] Figure 8 The diagrams show the band structure and coaxial model of carbon nanotubes with different diameters; (a) (3,3) band structure of armchair-type carbon nanotubes, (b) (6,6) band structure of armchair-type carbon nanotubes, (c) (9,9) band structure of armchair-type carbon nanotubes, and (d) coaxial model of three armchair-type carbon nanotubes with different diameters.

[0035] Figure 9 The following are density of states (DOS) diagrams for carbon nanotubes of different diameters: (a) (3,3) DOS diagram for armchair-type carbon nanotubes, (b) (6,6) DOS diagram for armchair-type carbon nanotubes, and (c) (9,9) DOS diagram for armchair-type carbon nanotubes. Detailed Implementation

[0036] The specific technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0037] The method of this invention performs simulation calculations on single-walled carbon nanotubes with similar diameters but different chirality and with similar chirality but different diameters, respectively. The specific operation steps are as follows:

[0038] Step 1: Calculation of chiral carbon nanotubes with similar diameters;

[0039] Using Materials Studio software, single-walled carbon nanotubes with different chiralities were modeled by controlling the tube diameter, and the basic parameters were adjusted and modified. The lattice parameters were expanded by 15~20 Å in the direction perpendicular to the tube axis, which effectively eliminated the influence of periodic boundaries on the results of each tube during the calculation process and avoided the mutual influence between carbon nanotubes on the calculation data.

[0040] The K-point convergence test of four chiral single-walled carbon nanotubes was performed using the DMol3 module in Materials Studio. The convergence condition was set at an adjacent energy difference of <0.01 eV to ensure high accuracy and reliability of the computational data. Based on the optimal K-point grid density determined by the convergence test, the initial crystal model was geometrically optimized using fine precision as the convergence criterion to obtain a stable crystal model.

[0041] The specific parameter settings are as follows:

[0042] Algorithm settings: The Perdew-Burke-Ernzerhof (PBE) function within the Generalized Gradient Approximation (GGA) is used to handle the exchange correlation function;

[0043] Atomic orbital basis sets: Double-numbered plus polarization (DNP);

[0044] The maximum number of loops is set to 300;

[0045] Adjust only the grid density at point K, adjusting in a single direction using 1*1*n;

[0046] The K-Points of each tube obtained through convergence testing were used to perform geometric optimization of the model. In the convergence accuracy settings, Energy, Max Force, and Max Displacement of atoms were each set to 1×10⁻⁶. -5 Ha, 0.002Ha / Å and 0.005Å, with the remaining parameters set to the default Fine precision of the Dmol3 module, and the maximum number of cycles set to 300 to ensure that each model is in the stable configuration with the lowest energy.

[0047] After geometric optimization, the electronic structure of each model is calculated, including band structure, density of states (DOS), and partial wave density of states (PDOS). Considering that single-walled carbon nanotubes are typical one-dimensional materials, the Brillouin zone path selection in the electronic structure calculation process only selects the most representative Γ-A path along the tube axis as the research object.

[0048] Step 2: Calculation of carbon nanotubes with the same chiral structure but different diameters;

[0049] Using Materials Studio software, single-walled carbon nanotubes with different diameters were modeled by further adjusting the tube diameter proportionally, and their electronic structure and mechanical properties were calculated.

[0050] Using the Castep module, we first performed convergence tests on single-walled carbon nanotubes with the same chiral structure but different diameters to determine the appropriate Ecut cutoff energy and K-Point. The convergence test criteria were consistent with those in step one, and the convergence condition was set to an adjacent energy difference of <0.01 eV.

[0051] When testing the cutoff energy, a K-point grid density of 1*1*n is selected, and other parameters are fixed. The corresponding energies under different cutoff energies are tested, and the cutoff energy corresponding to the lowest energy point is selected. Then, the K-point grid density is tested, the cutoff energy is selected, and other parameters are fixed. The energy under different K-point grid densities in one direction of 1*1*n is tested, and the K-point grid density corresponding to the lowest energy point is selected. The optimal K-point grid density and the cutoff energy of the convergent plane wave are determined.

[0052] Subsequently, geometric optimization was performed on the three types of carbon nanotubes using the aforementioned Ecut cutoff energy and K-point. The convergence criteria were set to 1×10T for Energy, Max Force, Max Stress, and Max Displacement. -5 eV / atom, 0.03 eV / Å, 0.05 GPa, and 0.001 Å, with other parameters set to default values ​​for fine precision. Based on the GGA-PBE functional, the TPSD structure optimization method was added, and the self-consistent convergence criterion (SCF tolerance) was set to 10. -6 eV / atom, energy convergence criterion is 1×10⁻⁶ -6 eV / atom; Max SCF cycles set to 500;

[0053] The mechanical property calculation was performed using the Castep module, with the strain loading step set to 4 steps and the maximum strain set to 0.003. The calculation results were then calculated and output.

[0054] Example 1

[0055] A first-principles method for evaluating the effects of chirality and diameter on the structure and properties of single-walled carbon nanotubes includes the following steps:

[0056] Step 1: Use Materials Studio software to model (6,6) armchair carbon nanotubes, (10,0) serrated carbon nanotubes, and (4,8) and (8,4) chiral carbon nanotubes respectively, controlling the tube diameter to be about 0.8 mm, and the error of the tube diameter to be controlled within 0.5 Å.

[0057] Table 1. Basic cell parameters of each model

[0058]

[0059] After modeling is completed, the vacuum layer in the direction perpendicular to the tube axis is expanded by 20 Å;

[0060] Based on density functional theory (DFT), the DMol3 module built into the software is used to calculate the energy of each tube, and the convergence of point K is tested.

[0061] The algorithm is configured to use the Perdew-Burke-Ernzerhof (PBE) function within the Generalized Gradient Approximation (GGA) to handle the exchange correlation function; atomic orbital basis set: double digital polarization (DNP); maximum number of iterations: 500; and other parameters use the default values ​​for fine precision.

[0062] Based on the premise that the total energy difference between two adjacent calculations is less than 0.01 eV, after completing the convergence test, the K-points with the highest accuracy were set as follows: (6,6) as 1×1×9; (10,0) as 1×1×9; (4,8) and (8,4) as 1×1×5. Geometric optimization was performed on each model, with the convergence criteria for energy, force, and displacement set according to the default parameters in the Fine precision of the Dmol3 module, and the maximum number of iterations set to 300. The configuration was fully optimized to make the model energy in the most stable configuration with the lowest possible energy.

[0063] After the geometric optimization reached the convergence criterion, the band structure, density of states, and partial density of states of each tube were calculated using the Γ-A path. The calculation results are as follows:

[0064] The dashed line represents the Fermi level, which is located approximately in the middle of the band gap. The electronic band structure describes the energy-momentum relationship of charge carriers within the first Brillouin zone. Below the Fermi level corresponds to the valence band, and above the Fermi level corresponds to the conduction band. The energy difference between the highest point of the valence band and the lowest point of the conduction band is the band gap. A smaller band gap indicates that less energy is required for electron transitions, and thus better conductivity.

[0065] like Figure 4 As shown, the (6,6) armchair-type carbon nanotube has a very small band gap of 0.012 eV, belonging to the direct band gap material. The valence band top and conduction band bottom intersect each other at the Fermi level, exhibiting metallic properties. The chiral carbon nanotubes of (10,0), (8,4) and (4,8) types have chirality of 0.725 eV, 0.780 eV and 0.80 eV, respectively, exhibiting semiconductor properties.

[0066] Band structure provides information on the distribution of electrons in momentum space, while density of states reveals the distribution of electronic states from an energy perspective. Combining the two can more completely describe the electronic properties of materials.

[0067] Figure 5 As shown, the density of states of (6,6) carbon nanotubes is consistent with the Fermi level calculated in the band structure, with a small band gap and a "V" shaped structure, which increases linearly with energy, further indicating that it has high electron mobility and good conductivity.

[0068] Chiral (10,0) zigzag carbon nanotubes have a wider band gap compared to (6,6) carbon nanotubes, making them typical semiconductor materials.

[0069] exist Figure 6 In the density of states of the chiral carbon nanotubes shown, the (8,4) and (4,8) chiral carbon nanotubes with helical symmetry both exhibit semiconductor characteristics. Due to the helical symmetry of these two types of chiral carbon nanotubes, their density of states is similar to that shown in the band structure, exhibiting almost the same density of states distribution.

[0070] Furthermore, within a single smallest basic periodic unit, (8,4) and (4,8) chiral carbon nanotubes contain 112 carbon atoms, far more than (6,6) and (10,0) carbon nanotubes. They also have a greater number of valence electrons participating in bonding. This is why the density of states of these two chiral carbon nanotubes is generally greater than that of (6,6) and (10,0) carbon nanotubes at <0 eV.

[0071] The total density of states (DOS) shows the overall electronic state distribution of a material, while the partial density of states (PDOS) can reflect the contributions of different atomic orbitals in more detail.

[0072] exist Figure 7 In the partial density of states, the PDOS of chiral (6,6) armchair-shaped carbon nanotubes and (10,0) serrated carbon nanotubes show that in the higher energy range (-7~7eV) near the Fermi level, the conduction band and valence band are mainly composed of 2p states, with virtually no s orbital components in between.

[0073] This is related to the bonding pattern of carbon atoms. Carbon atoms have six electrons outside the nucleus, arranged in a 1s² configuration. 2 2s 2 2p 2 During bonding, the four valence electrons of carbon undergo orbital hybridization. One 2s electron remains in the 2s orbital, while the other 2s electron hybridizes with the 2p orbital, forming sp, sp², or sp³ hybrid orbitals, corresponding to carbon-carbon triple, double, and single bonds, respectively. In carbon nanotubes, sp² and sp³ hybrid orbitals coexist. 2 and sp3 Hybridization means that most of the bonds formed by p orbitals are distributed near the Fermi level, and the spacing between π and π* is affected by the chirality of carbon nanotubes.

[0074] Armchair-shaped carbon nanotubes are generally considered to be a metallic material. However, for small-diameter armchair-shaped carbon nanotubes, due to the curvature effect, which becomes more pronounced as the tube diameter decreases, a narrow band gap of about 10 meV is formed.

[0075] By calculating the electronic structure of chiral single-walled carbon nanotubes with similar diameters in step one, we selected a metallic armchair-type single-walled carbon nanotube with high conductivity and further adjusted the diameter for more in-depth analysis.

[0076] Step Two:

[0077] Armchair-shaped carbon nanotubes with diameters of 0.407 nm, 0.814 nm, and 1.22 nm were modeled, with chirality of (3,3), (6,6), and (9,9), respectively.

[0078] After modeling is completed, the vacuum layer in the direction perpendicular to the tube axis is expanded by 20 Å;

[0079] Based on density functional theory (DFT), the DMol3 module built into the software was used to calculate the energy of each tube, and convergence tests were performed on the Ecut cutoff energy and K point.

[0080] The algorithm uses the Perdew-Burke-Ernzerhof (PBE) function within the Generalized Gradient Approximation (GGA) to handle the exchange correlation function; the structure optimization algorithm is an efficient structure optimization under TPSD-constrained unit cells; the atomic orbital basis set is dual-digital polarization (DNP); the maximum number of iterations is 500, and the remaining parameters use the default values ​​for fine precision;

[0081] Based on the premise that the total energy difference between two consecutive calculations is less than 0.01 eV, after completing the convergence test, the Ecut of (3,3) carbon nanotubes was set to 600 eV and the K point to 1×1×13, the Ecut of (6,6) carbon nanotubes was set to 625 eV and the K point to 1×1×9, and the Ecut of (9,9) carbon nanotubes was set to 650 eV and the K point to 1×1×9. Geometric optimization was performed on the above carbon nanotubes, and the convergence criteria Energy, Max force, Max stress, and Max displacement were set to 1×10⁻⁶ respectively. -5eV / atom, 0.03 eV / Å, 0.05 GPa, and 0.001 Å, with the remaining parameters set to default values ​​for fine accuracy. The self-consistent convergence criterion (SCF tolerance) is set to 10. -6 Max SCF cycles are set to 500; the configuration is fully optimized to achieve the lowest and most stable model energy; after obtaining the stable configuration, the electronic structure and mechanical calculations are performed again.

[0082] Figure 8 In the band structure of the medium tube, the band gaps of (3,3), (6,6) and (9,9) are 0.086eV, 0.012eV and 0.185eV respectively. However, their band gaps are much smaller than 0.4eV, so they exhibit conductor properties. Furthermore, as the tube diameter increases, the number of carbon atoms increases, and the number of valence bands and conduction bands also gradually increases.

[0083] Binding density of states diagram Figure 9 As can be seen, the density of electronic states in the model increases with the increase of the tube diameter. The sharper peak appearing near the Fermi level is caused by the van Hoff singularity.

[0084] The calculation of the mechanical properties of (3,3), (6,6) and (9,9) was performed in the Castep module, with the strain loading step set to 4 and the maximum strain set to 0.003.

[0085] Table 2 shows the Young's modulus of armchair-shaped carbon nanotubes with different tube diameters (X and Y represent the direction perpendicular to the tube axis, and Z represents the direction of the carbon nanotube along the tube axis).

[0086]

[0087] As a typical one-dimensional nanomaterial, carbon nanotubes exhibit anisotropy by measuring Young's modulus in different directions. The Young's modulus along the tube axis is much greater than that perpendicular to the tube axis. Furthermore, as the tube diameter increases, the number of carbon atoms increases, and the number of C-C bonds formed also increases, resulting in an increase in the Young's modulus perpendicular to the tube axis.

[0088] Unlike the X and Y directions, the Young's modulus of carbon nanotubes in the tube axis direction does not show a single trend. The Young's modulus of (6,6) chiral carbon nanotubes reaches its maximum value in the tube axis direction.

[0089] Table 3 shows the relevant mechanical properties of armchair-shaped carbon nanotubes with different diameters.

[0090]

[0091] Further experimental predictions of the mechanical properties of carbon nanotubes revealed that as the tube diameter gradually increases, all properties gradually increase. This is because as the tube diameter increases, the number of bonded carbon atoms in each unit of equal size increases, resulting in a more stable structure and superior mechanical properties.

[0092] In summary, based on first principles and density functional theory, we first optimize the structure of single-walled carbon nanotubes with similar diameters but different chiralities to obtain a stable configuration, and then perform relevant calculations on the electronic structure. According to the performance requirements of infrared stealth materials or other application fields, we select a suitable carbon nanotube type. Then, by adjusting the tube diameter, we explore the influence of tube diameter on the mechanical properties of carbon nanotubes, thereby providing a basis for the stability of high-performance applications of the material.

[0093] Through high-precision simulation, the microscopic mechanisms of the macroscopic properties of materials are revealed in depth, providing a theoretical basis for the high-performance application of carbon nanotubes with single chirality.

[0094] In particular, in some preferred embodiments of the present invention, a computer device is also provided, including a memory and a processor and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method for evaluating the chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first principles in any of the above embodiments.

[0095] In some other preferred embodiments of the present invention, a computer-readable storage medium is also provided, on which a computer program / instruction is stored, wherein when the computer program is executed by a processor, it performs the steps of evaluating the chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first principles in any of the above embodiments.

[0096] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments described above that evaluate the chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first principles, which will not be repeated here.

[0097] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for evaluating the effects of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations, characterized in that, Includes the following steps: Step 1: Construct initial crystal models of single-walled carbon nanotubes with similar diameters but different chiral structures; Step 2: Based on the initial crystal model in Step 1, conduct a K-point convergence test to determine the optimal K-point grid density; based on the optimal K-point grid density determined by the convergence test, use the fine precision as the convergence criterion to perform geometric optimization on the initial crystal model to obtain a stable crystal model. Step 3: Perform electronic structure calculations on the stable crystal model described in Step 2 to complete the analysis of the influence of chirality on the structure and properties of single-walled carbon nanotubes; Step 4: Construct initial crystal models of single-walled carbon nanotubes with the same chiral structure but different diameters; Step 5: Based on the initial crystal model in Step 4, conduct Ecut cutoff energy and K-point convergence tests to determine the optimal K-point grid density and convergent plane wave cutoff energy; based on the optimal K-point grid density and convergent plane wave cutoff energy determined by the convergence test, perform geometric optimization on the initial crystal model with fine precision as the convergence criterion to obtain a stable crystal model. Step 6: Perform electronic structure and mechanical property calculations on the stable crystal model described in Step 5 to complete the analysis of the influence of tube diameter on the structure and properties of single-walled carbon nanotubes.

2. The method for evaluating the effects of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations, as described in claim 1, is characterized in that... In step 1, after the initial crystal model is constructed, the thickness of the vacuum layer is increased by 15~25 Å in the direction perpendicular to the axis of the single-walled carbon nanotube; the diameter error is less than 0.5 Å in single-walled carbon nanotubes with similar diameters but different chiral structures.

3. The method for evaluating the effects of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations according to claim 1, characterized in that, In step 2, the K-point convergence test is performed using the Dmol3 module. Only the K-point density is adjusted. The Monkhorst-Pack grid is selected as the K-point sampling method. Different K-point grid densities are set. The grid density is 1*1*n in one direction. The optimal K-point grid density is determined based on the total energy difference between two adjacent calculations being less than 0.01eV.

4. The method for evaluating the effects of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations according to claim 3, characterized in that, In step 2, the initial crystal model is geometrically optimized using the DMol3 module. During the geometric optimization process, the GGA-PBE exchange-correlated functional and the dual numerical polarization basis set DNP are used to calculate the all-electronic structure. The self-consistent convergence criterion for geometric optimization is 1×10⁻⁶. -6 .

5. The method for evaluating the effects of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations according to claim 1, characterized in that, In step 3, the electronic structure calculation selects the Γ-A path along the tube axis in the Brillouin zone as a representative path, and calculates the band structure, density of states, and partial density of states along the path.

6. The method for evaluating the effects of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations according to claim 1, characterized in that, In step 4, after the initial crystal model is constructed, the thickness of the vacuum layer is increased by 15~25 Å in the direction perpendicular to the axis of the single-walled carbon nanotube.

7. The method for evaluating the effects of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations according to claim 1, characterized in that, In step 5, the cutoff energy and K-point convergence test are performed using the CASTEP module. When testing the cutoff energy, a K-point grid density of 1*1*n is selected, other parameters are fixed, and the corresponding energies under different cutoff energies are tested respectively. The cutoff energy corresponding to the lowest energy point is selected. Then, the K-point grid density is tested. The cutoff energy is selected, other parameters are fixed, and the energy under different K-point grid densities in a single direction of 1*1*n is tested respectively. The K-point grid density corresponding to the lowest energy point is selected. Based on the total energy difference between two adjacent calculations being less than 0.01eV, the optimal K-point grid density and the convergent plane wave cutoff energy are determined.

8. The method for evaluating the effect of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations according to claim 7, characterized in that, The initial crystal model was geometrically optimized using the CASTEP module. During the geometric optimization process, the GGA-PBE exchange-correlated functional was employed, combined with the TPSD structure optimization algorithm and the dual numerical polarization basis set DNP for all-electronic structure calculations. The self-consistent convergence criterion for geometric optimization was 10. -6 .

9. The method for evaluating the effects of chirality and tube diameter on the structure and properties of single-walled carbon nanotubes based on first-principles calculations according to claim 1, characterized in that, In step 6, the electronic structure calculation selects the Γ-A path along the tube axis in the Brillouin zone as a representative path to calculate the band structure and density of states along the path; the mechanical property calculation uses the Castep module, including Young's modulus, shear modulus, bulk modulus and fracture toughness.

10. A computer device, comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 9.

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