A low-temperature super-slick material design method based on molecular simulation

Abstract

The application discloses a low-temperature super-smooth material design method based on molecular simulation, comprising the following steps: according to the design environment temperature of the low-temperature super-smooth material, different beta-diketone molecules are designed by regulating the number and position of benzene rings in the central structure and the length and type of side chains; the melting point and reaction activity of the beta-diketone molecules are obtained by a molecular simulation method, and a diketone molecular structure with lower melting point and higher reaction activity is selected; and the physical object is prepared for verification; the diketone is calculated by using the molecular simulation method, the tautomerism proportion and LUMO-HOMO energy difference of the diketone are obtained, and the diketone molecule with higher chemical reaction activity is screened; and the diketone molecule meeting the chemical reaction activity is further calculated, the simulated melting point of the diketone is obtained, and the low-melting-point diketone capable of maintaining fluidity at low temperature is screened, so that the trial and error cost is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of lubrication materials technology, specifically relating to a method for designing low-temperature superlubricating materials based on molecular simulation. Background Technology

[0002] Lubricating oil, as the "blood" of moving mechanical parts, reduces energy dissipation during equipment operation and plays a vital role in reducing component wear. Especially for high-end precision equipment such as precision instruments and micro-motors, there is an urgent need to develop more efficient new lubricating materials to ensure their high precision and long service life performance requirements.

[0003] Superlubricity refers to a lubrication state where the coefficient of friction between two friction pairs is less than 0.01, and it is considered an important cutting-edge technology for solving friction and wear in mechanical equipment. Academic papers such as Tribology Letters 2010, 37(2), 343-352, and Langmuir 2013, 29(17), 5207-5213, reported a novel synthetic lubricating material, β-diketone. Taking EPND (1-(4-ethylphenyl)nonane-1,3-diketone), which is currently the most widely studied, as an example, it has two tautomers: keto and enol. Under suitable working environments and conditions, superlubricity can be achieved on metal surfaces through the tribochemical action of the keto form and the molecular orientation effect of the enol form.

[0004]

[0005] In practical applications, lubricating materials often need to withstand varying operating temperatures. For example, in various micro-motors used in automobiles and drones, the operating temperature of the lubricating oil can be as low as -40°C to cope with the frigid climate of high-latitude regions. However, the low-temperature application of β-diketones presents two problems. Firstly, due to the liquid crystal-like molecular structure of β-diketones, the strong intermolecular forces cause β-diketones to solidify at low temperatures, thus losing their lubricating ability. Secondly, the insufficient chemical activity of β-diketones at low temperatures makes it difficult for tribochemical reactions to occur, hindering the maintenance of good lubrication at low temperatures. To address this, patent ZL202211671021.7 adjusts the number of benzene rings and the length of the side chains of the diketone, changing the tautomer ratio of its keto and enol forms, thereby obtaining a diketone with sufficient chemical reactivity for different ambient temperatures.

[0006] While the chemical reactivity and crystallinity of diketones can theoretically be controlled by adjusting the number of benzene rings and the length of side chains at different ambient temperatures, in practice, it is necessary to first prepare a large number of diketones with different molecular structures and verify their reactivity and melting point at the target temperature. The workload for the entire preparation, formulation, and analysis is enormous. Therefore, compared with simple trial-and-error experiments, there is an urgent need to establish a more efficient design method for low-temperature superlubricating materials. Summary of the Invention

[0007] The purpose of this invention is to provide a low-temperature superlubricating material design method based on molecular simulation, which reduces the trial-and-error costs and workload of molecular designing β-diketones for different ambient temperatures.

[0008] To achieve the above objectives, the following technical solution is adopted: A method for designing low-temperature superlubricating materials based on molecular simulation includes the following steps: (1) Based on the design ambient temperature of the low-temperature superlubricating material, different β-diketone molecules were designed by controlling the number and position of the benzene ring in the central structure, as well as the length and type of the side chain; (2) The melting point and reactivity of the β-diketone molecule were obtained by molecular simulation, and the diketone molecule structure with a lower melting point and higher reactivity was selected; (3) Prepare physical samples for verification.

[0009] According to the above scheme, the β-diketone molecule in step (1) has the following structural formula:

[0010] Where X and Y are integers, and 0 ≤ X ≤ 2, 0 ≤ Y ≤ 2, 1 ≤ X + Y ≤ 2; R1 is C m H 2m+1 C m H 2m OCH3 or C m H 2m OOCH3, R2 is C n H 2n+1 C n H 2n OCH3 or C n H 2n OOCH3, where 1 ≤ m ≤ 10, 1 ≤ n ≤ 10, and both are integers.

[0011] According to the above scheme, step (2) includes the following steps: S1. The β-diketone molecule is subjected to quantum chemical simulation to obtain the tautomerism ratio and LUMO-HOMO energy difference. Specifically, the keto form ratio and LUMO-HOMO energy difference of EPND (1-(4-ethylphenyl)nonane-1,3-dione) are used as the standard. When the keto form ratio of the β-diketone molecule is greater than 10% and the LUMO-HOMO energy is lower than -2.97 eV, the β-diketone molecule is considered to have met the requirements for reactivity. In this way, β-diketone molecules with high reactivity are screened out. S2. Use simulation software to build the unit cell of β-diketone molecules with the required reactivity, optimize the geometry of the unit cell model, and then perform annealing. S3. Use scripts to perform molecular dynamics simulations on the annealed unit cell at different temperatures; S4. Extract the density of each frame of the unit cell trajectory file after molecular dynamics simulation, plot the density versus temperature graph, determine the mutation point, and use the temperature corresponding to the mutation point as the simulated melting point. When the simulated melting point is lower than the design ambient temperature, the β-diketone molecule is considered to meet the requirements.

[0012] According to the above scheme, step S1 includes the following steps: The enol and keto structures of the three diketones designed in step (1) were constructed and their geometry optimized. A deuterated chloroform solvent model was established (dielectric constant ε = 4.711 F / m, refractive index n = 1.445, surface tension coefficient γ = 27.14 mN / m, solvent radius r = 2.75 Å). The functional and basis set were set to B3LYP / 6-31G(d,p), and the convergence criterion was set to the strict level (root mean square of force < 0.00045 E). h / a0.、Energy change <10 -8 E h The keto and enol forms of the three diketones in the solvent model were further optimized. The Gibbs free energies of the keto and enol forms of the three diketones in deuterated chloroform were calculated, and the tautomerism ratio was obtained based on the Boltzmann distribution formula. The HOMO and LUMO energy levels were extracted from the output files of the three optimized diketone molecules, and the LUMO-HOMO energy difference was calculated. Diketones that meet the requirements of chemical reactivity were screened according to the tautomerism ratio and the LUMO-HOMO energy difference.

[0013] According to the above scheme, step S1 uses the ketone ratio of 10% and the LUMO-HOMO energy difference of -2.97 eV as the criteria for judging the reactivity of diketones. When the designed diketone molecule has a ketone ratio greater than 10% and a LUMO-HOMO energy difference less than -2.97 eV, the diketone molecule is considered to meet the activity requirements.

[0014] According to the above scheme, step S2 includes the following steps: For the diketone molecules selected in step S1 that meet the reactivity criteria, based on their optimized keto molecular configuration, an amorphous unit cell construction scheme was adopted. The initial unit cell size was set, and 100 molecules were filled to match the molecular packing density of the real system. Geometric optimization was carried out using a hybrid algorithm of steepest descent method, conjugate gradient method, and Newton's algorithm. The energy change value of 0.0001 kcal / mol, the maximum force of 0.005 kcal / mol / Å, and the maximum displacement of 0.00005 Å were used as convergence criteria to obtain the geometrically optimized unit cell. The optimized unit cell was then annealed with the following annealing parameters: 5 cycles, cycle start temperature of 200 K, cycle end temperature of 400 K, ensemble selection as canonical ensemble (NVT), and Berendsen algorithm for both temperature and pressure control. The annealed diketone unit cell was obtained after the simulation.

[0015] According to the above scheme, step S3 includes the following steps: An automated script adapted to the simulation software was developed to perform molecular dynamics simulations on the annealed diketone unit cell obtained in step S2. The script presets a temperature range from below to above the expected melting point, here set to 100 K-500 K, with a molecular dynamics simulation performed every 10 K. The ensemble was set to NPT, and the Berendsen algorithm was used for both temperature and pressure control. A time step of 1 fs was set, and each molecular dynamics simulation lasted 500 ps to ensure that the system fully relaxes and reaches thermodynamic equilibrium at each temperature. The script automatically calls the annealed unit cell structure and executes molecular dynamics simulations sequentially according to the preset temperature sequence. During the simulation, it periodically outputs trajectory files containing key parameters such as density and total energy, providing complete data support for the subsequent determination of the melting point abrupt change.

[0016] According to the above scheme, step S4 includes the following steps: Extract the system density data for each frame from the unit cell trajectory file output by the molecular dynamics simulation; then plot a line graph with temperature as the horizontal axis and density as the vertical axis to observe the trend of density change with temperature. When the temperature rises to a certain critical value, the system density will drop abruptly. The temperature corresponding to this abrupt change point is the simulated melting point of the diketone molecule; finally, compare the simulated melting point with the design ambient temperature. If the simulated melting point is lower than the design ambient temperature, the diketone molecule is determined to meet the design requirement of low melting point.

[0017] According to the above scheme, step (3) includes the following steps: The diketone molecular structure with a low melting point and high reactivity selected in step (2) was prepared by Claisen condensation reaction, and the actual melting point was obtained by differential scanning calorimetry. The actual melting point was compared with the simulated melting point in step (2) to verify the accuracy of the simulation.

[0018] According to the above scheme, step (3) also includes a friction test on the prepared diketone at the target design temperature to verify the superlubricating properties.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: Molecular simulations were used to calculate the tautomer ratios and LUMO-HOMO energy differences of diketones, thereby screening for diketone molecules with high chemical reactivity. Further calculations using molecular simulations were performed on diketone molecules that met the chemical reactivity criteria, yielding simulated melting points, thus screening for low-melting-point diketones that maintain fluidity at low temperatures.

[0020] This invention uses molecular simulation to design a diketone molecular structure that can maintain fluidity at low temperatures and has strong reactivity, thereby greatly reducing trial and error costs. Attached Figure Description

[0021] Figure 1 : Initial unit cell diagram of the first type of β-diketone.

[0022] Figure 2 The first type of β-diketone density-melting point line graph.

[0023] Figure 3 Friction curve of the second type of β-diketone at -10℃. Detailed Implementation

[0024] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0025] In specific implementation methods, the key to achieving superlubricity in β-diketone materials lies in the chelation reaction between the dicarbonyl functional group and the metal. Therefore, the diketone molecule should be designed according to the following structural formula range:

[0026] Where X and Y are integers, and 0 ≤ X ≤ 2, 0 ≤ Y ≤ 2, 1 ≤ X + Y ≤ 2; R1 is C m H 2m+1 C m H 2m OCH3 or C m H 2m OOCH3, R2 is C n H 2n+1 Cn H 2n OCH3 or C n H 2n OOCH3, where 1 ≤ m ≤ 10, 1 ≤ n ≤ 10, and both are integers.

[0027] Intermolecular forces determine the melting point of a substance. The intermolecular forces of diketones are mainly determined by two factors: dispersion forces (the greater the relative molecular mass, the greater the dispersion force) and π-π stacking interactions of the benzene ring (substituent electronic effects, steric hindrance effects, and aromatic ring conjugation systems all affect the magnitude of π-π interactions between benzene rings). First, determine the design operating temperature of the low-temperature superlubricating material. In order to reduce the intermolecular forces of the diketone and lower the melting point, design three diketones with smaller dispersion forces and π-π stacking effects of benzene rings.

[0028] Furthermore, the melting point and reactivity of the β-diketone molecule were obtained through molecular simulation, and diketone molecular structures with lower melting points and higher reactivity were selected: S1. The ketone ratio of EPND (10%, obtained by 1H NMR spectroscopy, solvent: deuterated chloroform) and the LUMO-HOMO energy difference of -2.97 eV are used to judge the reactivity of diketones. When the ketone ratio of the designed diketone molecule is greater than 10% and the LUMO-HOMO energy difference is less than -2.97 eV, the diketone molecule is considered to meet the reactivity requirements. Construct the enol and ketone structures of the three diketones designed in step (1) and perform geometric optimization. Establish a deuterated chloroform solvent model (dielectric constant ε = 4.711 F / m, refractive index n = 1.445, surface tension coefficient γ = 27.14 mN / m, solvent radius r = 2.75 Å). Set the functional and basis set to B3LYP / 6-31G(d,p) and the convergence criterion to the strict level (root mean square of force < 0.00045 E). h / a0.、Energy change <10 -8 E h The keto and enol forms of the three diketones in the solvent model were further optimized. The Gibbs free energies of the keto and enol forms of the three diketones in deuterated chloroform were calculated, and the tautomerism ratios were obtained based on the Boltzmann distribution formula. The HOMO and LUMO energy levels were extracted from the optimized diketone molecule output files, and the LUMO-HOMO energy difference was calculated. Diketones meeting the chemical reactivity requirements were screened based on the tautomerism ratios and the LUMO-HOMO energy difference.

[0029] S2. For the diketone molecules selected in step S1 that meet the reactivity criteria, based on their optimized keto molecular configuration, an amorphous unit cell construction scheme is adopted. The initial unit cell size is set, and 100 molecules are filled to match the molecular packing density of the real system. Geometric optimization is performed using a hybrid algorithm of the steepest descent method, the conjugate gradient method, and Newton's algorithm. The energy change value of 0.0001 kcal / mol, the maximum force of 0.005 kcal / mol / Å, and the maximum displacement of 0.00005 Å are used as convergence criteria to obtain the geometrically optimized unit cell. The optimized unit cell is then annealed with the following parameters: 5 cycles, a cycle start temperature of 200 K, a cycle end temperature of 400 K, a canonical ensemble (NVT) selected, and the Berendsen algorithm for both temperature and pressure control. The annealed diketone unit cell is obtained after the simulation.

[0030] S3. Develop an automated script adapted to the simulation software to perform molecular dynamics simulations on the annealed diketone unit cell obtained in step S2. The script presets a temperature range from below to above the expected melting point; here, the range is set to 100 K-500 K. Molecular dynamics simulations are performed every 10 K. The ensemble is set to NPT, and the Berendsen algorithm is used for both temperature and pressure control. A time step of 1 fs is set, and each molecular dynamics simulation lasts 500 ps to ensure the system fully relaxes and reaches thermodynamic equilibrium at each temperature. The script automatically calls the annealed unit cell structure and executes molecular dynamics simulations sequentially according to the preset temperature sequence. During the simulation, it periodically outputs trajectory files containing key parameters such as density and total energy, providing complete data support for subsequently determining the melting point abrupt change.

[0031] S4. Extract the system density data for each frame from the unit cell trajectory file output by the molecular dynamics simulation. Then, plot a line graph with temperature on the horizontal axis and density on the vertical axis to observe the density change with temperature. When the temperature rises to a certain critical value, the system density undergoes a sudden decrease. This is a typical characteristic of the unit cell transforming from a solid-state ordered structure to a liquid-state disordered structure. The temperature corresponding to this abrupt change point is the simulated melting point of the diketone molecule. Finally, compare the simulated melting point with the design ambient temperature. If the simulated melting point is lower than the design ambient temperature, the diketone molecule is determined to meet the low melting point design requirement.

[0032] Finally, a diketone that meets the requirements of low melting point and reactivity was prepared by Claisen condensation reaction, and the actual melting point was obtained by differential scanning calorimetry. The actual melting point was compared with the simulated melting point to verify the accuracy of the simulation. The prepared diketone was subjected to friction test at the target design temperature to verify its superlubricating properties.

[0033] Example 1 Step 1: Constructing a diketone molecular model The minimum operating temperature of the lubricating oil was set to -10℃ (263.15 K). Enol and ketone structures of three diketones with different numbers of benzene rings were constructed using simulation software. Geometric optimization of the three enol and ketone structures was performed using the B3LYP-D3(BJ) / 6-31G(d,p) functional basis set. The convergence criterion was set to a strict level (root mean square force < 0.00045E). h / a0.、Energy change <10 -8 E h To ensure the accuracy of structural optimization and electronic energy calculations, the temperature was set to 25℃ (298.15K). After optimization, three stable keto and enol structures of diketone molecules were obtained. Specifically: for the first diketone, X is 0, Y is 0, R1 is C2H5, and R2 is C1H3; for the second diketone, X is 1, Y is 0, R1 is C2H5, and R2 is C1H3; for the third diketone, X is 1, Y is 1, R1 is C2H5, and R2 is C1H3.

[0034] Step 2: Determine the reactivity of the diketone molecule. Using an implicit solvent model (SMD), the key physical parameters of deuterated chloroform (dielectric constant ε = 4.711 F / m, refractive index n = 1.445, surface tension coefficient γ = 27.14 mN / m, solvent radius r = 2.75 Å) were used in the quantization software to establish the keto and enol structures of three diketones in deuterated chloroform solvent. The temperature was set to 298.15 K (25 °C), and geometric optimization was performed. The convergence criterion remained strict (root mean square force < 0.00045 E). h / a0.、Energy change <10 -8 E h The functional basis set is chosen as B3LYP-D3(BJ) / 6-31G(d,p), based on the formula G=E. elec +G corr (E) elec For electron energy, G corr The Gibbs free energy was calculated using the Gibbs free energy correction term: the gas-phase Gibbs free energies of the keto forms of the three diketones are -826.4153 E. h -851.7629 E h -798.2516 E h The Gibbs free energies of the enol gas phase are -826.4328E. h -851.7831 E h -798.2849 E h The solvation free energies of the ketone form are -0.0208 E. h -0.0211 Eh -0.0205 E h The solvation free energies of the enol form are -0.0225 E. h -0.0230 E h -0.0228 E h The phase free energies of the superimposed ketone solutions are -826.4361 E. h -851.7840 E h -798.2721 E h The free energies of the enol solution phase are -826.4553 E. h -851.8061 E h -798.3077 E h Based on the Boltzmann distribution, the keto proportions of the three diketones were calculated to be 22%, 17%, and 7%. The HUMO-LUMO energies of the diketone keto structures were then calculated: -3.14 eV for the first diketone, -2.99 eV for the second, and -2.55 eV for the third. This indicates that the first and second diketones meet the requirements for chemical reactivity.

[0035] Step 3: Construct the unit cell of the diketone and perform structural optimization and annealing. Establish the initial unit cell for the first diketone as follows: Figure 1 As shown, the force field and charge are set, the length, width, and height of the unit cell are set to 30 Å, 30 Å, and 30 Å respectively, and the density is set to 0.9 g / cm³. 3 The number of elements is set to 100. Ten frames of configuration are output, and the frame with the lowest energy is selected. The model is then geometrically optimized using a hybrid algorithm combining the steepest descent method, conjugate gradient method, and Newton's method. The convergence criteria are energy change of 0.0001 kcal / mol, maximum force of 0.005 kcal / mol / Å, and maximum displacement of 0.00005 Å. The resulting geometrically optimized unit cell is then obtained. The optimized model is annealed for 5 cycles at a starting temperature of 200 K and a ending temperature of 400 K. The ensemble is selected as the canonical ensemble (NVT), and the temperature control algorithm is Berendsen. The same operation is performed on the second diketone.

[0036] Step 4: Perform variable-temperature molecular dynamics simulations on the model. A variable-temperature molecular dynamics script was written in Perl to perform molecular dynamics simulations on two diketone unit cell models after annealing. The ensemble was set to isothermal and isobaric (NPT), the initial velocity was set according to the Boltzmann distribution, the step duration was set to 1 fs, the simulation duration was set to 500 ps, ​​the temperature and pressure control were set to the Berendsen algorithm, and the temperatures were set to 500 K, 490 K, 480 K...100 K for molecular dynamics simulations.

[0037] Step 5: Simulate the melting point of diketones The script extracts parameters such as density, volume, and diffusion coefficient from each frame of the trajectory file after molecular dynamics simulations of the first type of diketone unit cell at different temperatures, and plots a line graph of density versus temperature, as shown below. Figure 2 As shown. The temperature corresponding to the mutation point was taken as the simulated melting point of the first diketone, which was 290 K, greater than 263.15 K, indicating that the first diketone did not meet the low melting point requirement; similarly, the same operation was performed on the second diketone, and the simulated melting point was 260 K, less than 263.15 K, which met the requirement.

[0038] Step Six: Preparation of the Target Diketone Product After obtaining a second diketone with higher reactivity and lower melting point through simulation, the target diketone was prepared using the Claisen condensation reaction. The specific process is as follows: Sodium ethoxide was added to ethyl malonate at -5°C until the solution turned yellow. After adding aryl ethyl ketone, the temperature was lowered to 0°C and the mixture was stirred for 24 hours. After obtaining the suspension, ethyl acetate and deionized water were added for extraction. Sodium chloride was added during back-extraction to promote separation. The organic phase was dried with anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation. The second diketone was then separated and purified by thin-layer chromatography using cyclohexane-ethyl acetate as the eluent.

[0039] Step 7: Determine the melting point of the diketone using a differential scanning calorimeter. Take 5 mg of the prepared target diketone, set the heating and cooling rates to 5 °C / min, heat from the initial temperature of -40 °C to the final temperature of 100 °C, and then cool from the final temperature of 100 °C back to the initial temperature of -40 °C to eliminate the influence of the material's thermal history on the test. Then heat from the initial temperature of -40 °C back to the final temperature of 100 °C and measure the melting point of the substance to -10.2 °C (263 K). Compare this result with the simulated melting point of 260 K to prove the accuracy of the melting point simulation.

[0040] Step 8: Verify the superlubricating properties of diketones at low temperatures. Rotational friction tests were conducted on the target diketone using a steel ball-disc system. The load, speed, test time, and ambient temperature were set to 16 N, 300 mm / s, 4 h, and -10℃, respectively. Superlubricity was achieved after a 1.5 h break-in period. Figure 3As shown, this demonstrates that the target diketone can achieve superlubricity at low temperatures.

[0041] Example 2 The difference between this embodiment and Case 1 is that the minimum operating temperature of the lubricating oil is set to -20℃, and the side chain lengths of the three designed β-diketones are different (for the first diketone, X is 1, Y is 0, R1 is C2H5, and R2 is C3H7; for the second diketone, X is 1, Y is 0, R1 is C1H3, and R2 is C3H7; for the third diketone, X is 1, Y is 0, R1 is C2H5, and R2 is C6H5). 13 The other steps and parameters are the same as in Implementation Case 1. Finally, the first diketone was obtained that met the requirements, with a simulated ketone ratio of 16%, a LUMO-HOMO energy difference of -3.44 eV, a melting point of -23.2℃, and superlubricity at -20℃ for 2 hours.

[0042] Example 3 This embodiment differs from Case 2 in that the minimum operating temperature of the lubricating oil is set to -25℃, and the three β-diketones designed have different side chain types (the first diketone has X = 1, Y = 0, R1 = C2H5, R2 = C1H2OCH3; the second diketone has X = 1, Y = 0, R1 = C1H2OCH3, R2 = C2H5; the third diketone has X = 1, Y = 0, R1 = C2H5, R2 = C1H2OOCH3). Other steps and parameters are the same as in Case 1. The third diketone ultimately meets the requirements, with a simulated ketone ratio of 21%, a LUMO-HOMO energy difference of -2.99 eV, a melting point of -26.4℃, and achieves superlubricity after 1.5 hours at -25℃.

Claims

1. A method for designing low-temperature superlubricating materials based on molecular simulation, characterized in that... Includes the following steps: (1) Based on the design ambient temperature of the low-temperature superlubricating material, different β-diketone molecules were designed by controlling the number and position of the benzene ring in the central structure, as well as the length and type of the side chain; (2) The melting point and reactivity of the β-diketone molecule were obtained by molecular simulation, and the diketone molecule structure with a lower melting point and higher reactivity was selected; (3) Prepare physical samples for verification.

2. The method for designing low-temperature superlubricating materials based on molecular simulation as described in claim 1, characterized in that... The β-diketone molecule described in step (1) has the following structural formula: Where X and Y are integers, and 0 ≤ X ≤ 2, 0 ≤ Y ≤ 2, 1 ≤ X + Y ≤ 2; R1 is C m H 2m+1 C m H 2m OCH3 or C m H 2m OOCH3, R2 is C n H 2n+1 C n H 2n OCH3 or C n H 2n OOCH3, where 1 ≤ m ≤ 10, 1 ≤ n ≤ 10, and both are integers.

3. The method for designing low-temperature superlubricating materials based on molecular simulation as described in claim 1, characterized in that... Step (2) includes the following steps: S1. The β-diketone molecule is subjected to quantum chemical simulation to obtain the tautomerism ratio and LUMO-HOMO energy difference. Specifically, the keto form ratio and LUMO-HOMO energy difference of EPND (1-(4-ethylphenyl)nonane-1,3-dione) are used as the standard. When the keto form ratio of the β-diketone molecule is greater than 10% and the LUMO-HOMO energy is lower than -2.97 eV, the β-diketone molecule is considered to have met the requirements for reactivity. In this way, β-diketone molecules with high reactivity are screened out. S2. Use simulation software to build the unit cell of β-diketone molecules with the required reactivity, optimize the geometry of the unit cell model, and then perform annealing. S3. Use scripts to perform molecular dynamics simulations on the annealed unit cell at different temperatures; S4. Extract the density of each frame of the unit cell trajectory file after molecular dynamics simulation, plot the density versus temperature graph, determine the mutation point, and use the temperature corresponding to the mutation point as the simulated melting point. When the simulated melting point is lower than the design ambient temperature, the β-diketone molecule is considered to meet the requirements.

4. The method for designing low-temperature superlubricating materials based on molecular simulation as described in claim 3, characterized in that... Step S1 includes the following steps: The enol and keto structures of the three diketones designed in step (1) were constructed and their geometry optimized. A deuterated chloroform solvent model was established (dielectric constant ε = 4.711 F / m, refractive index n = 1.445, surface tension coefficient γ = 27.14 mN / m, solvent radius r = 2.75 Å). The functional and basis set were set to B3LYP / 6-31G(d,p), and the convergence criterion was set to the strict level (root mean square of force < 0.00045 E). h / a0., Energy change < 10 -8 E h The keto and enol forms of the three diketones in the solvent model were further optimized. After calculating the Gibbs free energies of the keto and enol forms of the three diketones in deuterated chloroform, the tautomerism ratio was obtained based on the Boltzmann distribution formula. The HOMO and LUMO energy levels were extracted from the output files of the three optimized diketone molecules, and the LUMO-HOMO energy difference was calculated. Diketones that meet the requirements of chemical reactivity were screened according to the tautomerism ratio and the LUMO-HOMO energy difference.

5. The method for designing low-temperature superlubricating materials based on molecular simulation as described in claim 3, characterized in that... Step S1 uses the keto ratio of 10% for EPND and the LUMO-HOMO energy difference of -2.97 eV as the criteria for judging the reactivity of diketones. When the designed diketone molecule has a keto ratio greater than 10% and the LUMO-HOMO energy difference is less than -2.97 eV, the diketone molecule is considered to meet the reactivity requirements.

6. The method for designing low-temperature superlubricating materials based on molecular simulation as described in claim 3, characterized in that... Step S2 includes the following steps: For the diketone molecules selected in step S1 that meet the reactivity criteria, based on their optimized keto molecular configuration, an amorphous unit cell construction scheme was adopted. The initial unit cell size was set, and 100 molecules were filled to match the molecular packing density of the real system. Geometric optimization was carried out using a hybrid algorithm of steepest descent method, conjugate gradient method, and Newton's algorithm. The energy change value of 0.0001 kcal / mol, the maximum force of 0.005 kcal / mol / Å, and the maximum displacement of 0.00005 Å were used as convergence criteria to obtain the geometrically optimized unit cell. The optimized unit cell was then annealed with the following annealing parameters: 5 cycles, cycle start temperature of 200 K, cycle end temperature of 400 K, ensemble selection as canonical ensemble (NVT), and Berendsen algorithm for both temperature and pressure control. The annealed diketone unit cell was obtained after the simulation.

7. The method for designing low-temperature superlubricating materials based on molecular simulation as described in claim 3, characterized in that... Step S3 includes the following steps: An automated script adapted to the simulation software was developed to perform molecular dynamics simulations on the annealed diketone unit cell obtained in step S2. The script presets a temperature range from below to above the expected melting point, here set to 100K-500K, with a molecular dynamics simulation performed every 10K. The ensemble was set to NPT, and the Berendsen algorithm was used for both temperature and pressure control. A time step of 1 fs was set, and each molecular dynamics simulation lasted 500 ps to ensure that the system fully relaxes and reaches thermodynamic equilibrium at each temperature. The script automatically calls the annealed unit cell structure and executes molecular dynamics simulations sequentially according to the preset temperature sequence. During the simulation, it periodically outputs trajectory files containing key parameters such as density and total energy, providing complete data support for the subsequent determination of the melting point abrupt change.

8. The method for designing low-temperature superlubricating materials based on molecular simulation as described in claim 3, characterized in that... Step S4 includes the following steps: Extract the system density data for each frame from the unit cell trajectory file output by the molecular dynamics simulation; then plot a line graph with temperature as the horizontal axis and density as the vertical axis to observe the trend of density change with temperature. When the temperature rises to a certain critical value, the system density will drop abruptly. The temperature corresponding to this abrupt change point is the simulated melting point of the diketone molecule; finally, compare the simulated melting point with the design ambient temperature. If the simulated melting point is lower than the design ambient temperature, the diketone molecule is determined to meet the design requirement of low melting point.

9. The method for designing low-temperature superlubricating materials based on molecular simulation as described in claim 1, characterized in that... Step (3) includes the following steps: The diketone molecular structure with a low melting point and high reactivity selected in step (2) was prepared by Claisen condensation reaction, and the actual melting point was obtained by differential scanning calorimetry. The actual melting point was compared with the simulated melting point in step (2) to verify the accuracy of the simulation.

10. The method for designing low-temperature superlubricating materials based on molecular simulation as described in claim 9, characterized in that... Step (3) also includes a friction test on the prepared diketone at the target design temperature to verify its superlubricating properties.

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