A method and system for designing and predicting two-dimensional multiferroic hydroxide materials

Abstract

The application discloses a design and prediction method and system of a two-dimensional multiferroic hydroxide material, and the method is as follows: a standard three-dimensional hydroxide XOOH bulk crystal structure file is acquired, the file is cut by using visual software and a vacuum layer is added in the c direction, and the structure file type is converted into a.vasp file format by means of VESTA software; structure optimization calculation is carried out on the constructed hydroxide monolayer system, and the ferroelectric spontaneous polarization and the ferroelastic spontaneous strain direction are determined; the hydroxyl in the system is rotated and in-plane stress is applied, other ferroelectric phases and ferroelastic phases of the system are found, intermediate phases are found by respectively inserting points between the two ferroelectric phases and the two ferroelastic phases, and the reversal energy barrier between the two ferroelectric phases and the two ferroelastic phases is respectively calculated; the change of the ferroelectric polarization of the system along the ferroelastic transition path is calculated, and the internal mechanism of the coupling of the two ferroelectricities is explained. The method and system platform reduce the experimental trial and error cost, and realize screening / prediction of a two-dimensional ferroelectric and ferroelastic coupled multiferroic material.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, and more specifically, to a method for predicting the properties of multiferroic hydroxide materials based on first-principles calculations. Background Technology

[0002] Multiferroic materials are an important type of quantum condensed matter, encompassing multifunctional materials exhibiting ferroelectric, ferromagnetic / antiferromagnetic, or ferroelastic properties. Their ordering parameters include polarization, spin polarization, and strain. Under external influences, these properties can reversibly interconvert. A material containing two or more ferroic properties is called a multiferroic material, and different ordered states can be coupled and mutually modulated by different external fields. Compared to the spin-moment-dependent ferromagnetism / antiferromagnetism in ferromagnetic and ferroelastic multiferroic materials, ferroelectricity and ferroelasticity are intrinsically linked to the crystal structure. Therefore, if ferroelectricity and ferroelasticity coexist in the same system, these two properties are more likely to achieve strong coupling, and their polarization states along different plane axes can be controlled by applying mechanical stress. Consequently, ferroelectric and ferroelastic coupled multiferroic materials are widely used in non-volatile memories, not only maintaining stored data even without power supply but also significantly reducing power consumption.

[0003] Such materials are widely found in oxides, such as layered oxide Bi₂WO₆ films and perovskite-type BiFeO₃ films, and have been experimentally reported and confirmed. However, due to the strong ionic interactions, mechanical exfoliation of oxides is difficult, which limits the development of few-layer layered oxide materials. The successful experimental synthesis of rhenium disulfide, a multiferroic material coupled with two-dimensional van der Waals ferroelectric and ferroelastic properties, represents a breakthrough, but experimental data on this type of material is scarce. To design and find more high-performance two-dimensional multiferroic materials, it is necessary to simultaneously consider reducing experimental trial-and-error costs. In addition to focusing on ferromagnetic-ferroelectric and ferromagnetic-ferroelastic multiferroic materials, screening two-dimensional ferroelectric-ferroelastic multiferroic materials is of significant scientific importance. Based on first-principles calculations, some two-dimensional ferroelectric-ferroelastic multiferroic materials have been successfully predicted, such as ZrI₂ monolayers, Bi₂O₂Se monolayers, BP₅ monolayers, and γ-FeOOH monolayers. However, ultrathin two-dimensional systems are constrained by instabilities caused by large depolarization fields, which suppress ferroelectric polarization perpendicular to the surface. Furthermore, to promote the coexistence of ferroelasticity and ferroelectricity, relatively strict crystal symmetry is required. Screening two-dimensional ferroelectric and ferroelectric coupled multiferroic materials will help with further industrial applications.

[0004] Metal hydroxide monolayers with space group Pmn21 exhibit both ferroelectric and ferroelastic properties due to their unique structural characteristics. Furthermore, their stable crystal structure and exfoliation energy, similar to graphene, demonstrate their strong experimental feasibility. The rotation of hydroxyl groups in this system significantly contributes to multiferroic properties. On one hand, it can induce two ferroelectric polarization states, switching between them via a low-barrier antiferroelectric phase rather than a high-barrier paraelectric phase. On the other hand, the in-plane polarization can be modulated ferroelasticly. Under stress, the change in the spontaneous strain direction of the ferroelastic process is accompanied by the rotation of hydroxyl groups, i.e., a change in polarization direction, thus achieving ferroelectric-ferroelastic coupling. However, current theoretical studies of this type of hydroxide have not highlighted the contribution of hydroxyl rotation in the selection of the ferroelastic transition path. Therefore, designing such monolayers and finding a novel ferroelastic transition path method has significant guiding significance and application value for experiments.

[0005] Existing technologies have the following problems: high experimental difficulty and high trial-and-error costs; to date, there are few two-dimensional multiferroic materials coupled with ferroelectricity and ferroelasticity, and it is difficult to screen such two-dimensional materials by calculation. Summary of the Invention

[0006] To address the problems of existing technologies, the present invention aims to overcome the shortcomings of existing technologies and provide a method and system for designing and predicting two-dimensional multiferroic hydroxide materials. This method utilizes hydroxyl rotation to achieve ferroelastic switching, enabling the screening, prediction, and design of a novel class of two-dimensional multiferroic materials. The advantages of this invention are: reduced experimental trial-and-error costs; the realization of screening / prediction of two-dimensional ferroelectric and ferroelastic coupled multiferroic materials; and the provision of a ferroelectric and ferroelastic coupling method based on hydroxyl rotation. The achievable technical effect is: prediction of a class of ferroelectric and ferroelastic coupled two-dimensional multiferroic materials.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for designing and predicting two-dimensional multiferroic hydroxide materials is disclosed, which utilizes hydroxyl rotation to achieve ferroelastic coupling and screens and predicts two-dimensional multiferroic hydroxide materials with ferroelectric and ferroelastic coupling. The steps are as follows:

[0009] Step S1: Obtain the crystal structure file of a standard three-dimensional hydroxide bulk using a crystal database; perform cleavage and cutting of the three-dimensional hydroxide bulk using visualization software; and increase the thickness of the vacuum layer in the c-direction; use VESTA software to convert the crystal structure file type to .vasp file format to obtain the hydroxide monolayer system.

[0010] Step S2: Perform first-principles calculations to optimize the structure of the hydroxide monolayer system constructed in step S1 to obtain a stable structure; determine the ferroelectric spontaneous polarization and ferroelastic spontaneous strain directions of the hydroxide monolayer system;

[0011] Step S3: By rotating the hydroxyl groups in the hydroxide monolayer system and applying in-plane stress, find other ferroelectric and ferroelastic phases in the hydroxide monolayer system. Based on the symmetry of the hydroxide monolayer system, find the intermediate phases respectively, and calculate the flipping energy barriers between the two ferroelectric phases and the two ferroelastic phases respectively.

[0012] Step S4: Calculate the change of ferroelectric polarization of the hydroxide monolayer system with the ferroelastic transition path, obtain the ferroelectric-ferroelastic coupling relationship, and thus predict the two-dimensional multiferroic hydroxide material with ferroelectric and ferroelastic coupling.

[0013] Preferably, in step one, the chemical formula of the three-dimensional hydroxide is XOOH, wherein X is at least one of Sc and Al.

[0014] Preferably, step S1 is as follows:

[0015] Step S1.1: Using the three-dimensional hydroxide bulk obtained from the crystal database as the initial structure, gradually increase the interlayer distance and perform self-consistent calculations until the system energy tends to stabilize. The difference between the energy of this structure and the initial structure can be used to obtain the system exfoliation energy.

[0016] Step S1.2: Using visualization software, the three-dimensional hydroxide block structure is cut into two-dimensional single layers, and the thickness of the vacuum layer is increased in the c-direction, with the thickness of the vacuum layer set to... To eliminate interlayer interactions;

[0017] Step S1.3: Using VESTA software, convert the crystal structure file type to .vasp file format to obtain the hydroxide monolayer system.

[0018] Preferably, in step S1, the crystal structure file of a standard three-dimensional hydroxide block is obtained using the Materials Project crystal database.

[0019] Preferably, step S2 is as follows:

[0020] Step S2.1: Optimize the atomic positions and cell volume of the hydroxide monolayer system, setting the parameters to ISIF=3, IBRION=2, and using the conjugate gradient algorithm; the force convergence criterion is set to less than 3 for each atom. The energy convergence criterion is 10. -6 eV;

[0021] Step S2.2: After the convergence criterion is met, proceed to the next step of electronic structure calculation, and it can be found that all systems are semiconductors;

[0022] Step S2.3: By performing ab initio molecular dynamics simulations (AIMD) on the hydroxide monolayer system, and simultaneously calculating its phonon spectrum and elastic constants, the thermodynamic, kinetic, and mechanical stability of the structure is confirmed.

[0023] Preferably, step S3 is as follows:

[0024] Step S3.1: Rotate both hydroxyl groups in the hydroxide monolayer system by 180° along the c-axis to obtain another stable ferroelectric phase; rotate only one hydroxyl group to obtain the antiferroelectric phase; use the antiferroelectric phase as the intermediate phase, insert points between the antiferroelectric phase and the two ferroelectric phases respectively, and calculate the ferroelectric inversion energy barrier by using the climbing elastic band (CI-NEB) method.

[0025] Step S3.2: Calculate the ferroelectric polarization value P of the system using modern polarization theory based on the Berry phase method;

[0026] Step S3.3: Apply uniaxial tensile strain to the short axis (b-axis) of the initial ferroelastic variant to switch the short axis of the lattice to the a-axis, thereby generating another stable ferroelastic variant; based on the structural symmetry and the position of the hydroxyl groups in the two ferroelastic variants, take the structure in which the hydroxyl groups are arranged along the c-axis as the ciselastic phase, insert a point between the ciselastic phase and the two ferroelastic phases, perform NEB calculations, and obtain the ferroelastic inversion energy barrier;

[0027] Step S3.4: Calculate the reversible ferroelastic strain of the system according to the reversible ferroelastic strain formula |a / b-1|×100%, where a and b represent the lattice constants of the system.

[0028] Preferably, step S4 is as follows:

[0029] Step S4.1: Calculate the polarization value of each structure in the iron ball's flipping path and observe its changes;

[0030] Step S4.2: Observe the change in the hydroxyl direction in each structure of the ferroelastic flipping path; thereby predicting the ferroelectric-ferroelastic coupling performance of the two-dimensional multiferroic hydroxide material coupled with ferroelectricity and ferroelasticity.

[0031] A system for designing and predicting two-dimensional multiferroic hydroxide materials is provided. The system program executes the design and prediction method for two-dimensional multiferroic hydroxide materials described in this invention, and performs screening and prediction of two-dimensional multiferroic hydroxide materials with ferroelectric and ferroelastic coupling.

[0032] Compared with the prior art, the present invention has the following obvious and prominent substantive features and significant advantages:

[0033] 1. This invention reduces the trial-and-error costs of experimental screening operations by screening out two-dimensional multiferroic materials with excellent properties through calculations based on first-principles calculations. Furthermore, the operation is simple and easy to implement, and it can also guide experiments, avoiding high costs and blind spots.

[0034] 2. This invention designs a novel type of two-dimensional ferroelectric-ferroelastic coupled multiferroic material, providing a new platform for studying multiferroic coupling effects;

[0035] 3. This invention proposes a novel ferroelastic transition path, which allows the ferroelectric-ferroelastic coupling mechanism to be explained by the rotation of hydroxyl groups in the system. Attached Figure Description

[0036] Figure 1 The figure shows the variation of the exfoliation energy of the XOOH (X = Sc, Al) monolayer as a function of the interlayer distance (d - d0) in the examples. The inset shows a side view of XOOH blocks and monolayers with different interlayer distances.

[0037] Figure 2 The diagram shows the monolayer, band structure, and density of states of XOOH (X = Sc, Al) in the examples. Figure 2 (a) and Figure 2 (b) Results for Example 1 (ScOOH monolayer) and Example 2 (AlOOH monolayer), respectively.

[0038] Figure 3 The image shows the phonon spectrum of the XOOH (X = Sc, Al) monolayer in the example. Figure 3 (a) and Figure 3 (b) Results for Example 1 (ScOOH monolayer) and Example 2 (AlOOH monolayer), respectively.

[0039] Figure 4 The diagram shows the energy evolution over time of the XOOH (X = Sc, Al) monolayer under molecular dynamics simulation at T = 300 K in the examples. The insets show the side and top views of the XOOH structure after 1 ps of simulation. Figure 4 (a) and Figure 4 (b) Results for Example 1 (ScOOH monolayer) and Example 2 (AlOOH monolayer), respectively.

[0040] Figure 5 The diagram shows the ferroelectric and ferroelastic properties of the XOOH (X = Sc, Al) monolayer in the example. Figure 5 (a) is a schematic diagram of the ferroelectric phase transition of an XOOH monolayer. Figure 5 (b) shows the minimum ferroelectric phase transition path obtained by the CINEB method. Figure 5 (c) is a schematic diagram of the ferroelastic phase transition of an XOOH monolayer. Figure 5(d) Minimal ferroelastic phase transition path obtained by the CINEB method.

[0041] Figure 6 The energy curve for the rotation of hydroxyl groups in the XOOH (X = Sc, Al) monolayer along the c-direction is shown in the example. The minimum energy value is set to 0 as a reference. Figure 6 (a) and Figure 6 (b) Results for Example 1 (ScOOH monolayer) and Example 2 (AlOOH monolayer), respectively.

[0042] Figure 7 The spontaneous polarization value of the AlOOH monolayer in Example 1 varies with the ferroelastic reversal path. Detailed Implementation

[0043] This invention provides a method for predicting the multiferroic properties of two-dimensional hydroxides based on first-principles calculations. The invention will be described in detail below with reference to the accompanying drawings and specific preferred embodiments:

[0044] Example 1

[0045] In this embodiment, a method for designing and predicting two-dimensional multiferroic hydroxide materials is presented. This method utilizes hydroxyl rotation to achieve ferroelasticity and ferroelastic coupling, and screens and predicts two-dimensional multiferroic hydroxide materials with ferroelectric and ferroelastic coupling. The steps are as follows:

[0046] Step S1: Obtain the AlOOH crystal structure file with standard space group number 36 using the Materials Project crystal database. Perform cleaving and cutting on the structure using visualization software, and increase the thickness of the vacuum layer in the c-direction. Use VESTA software to convert the structure file type to .vasp file format. Step S1 includes the following steps:

[0047] Step S1.1: Using bulk AlOOH as the initial structure, gradually increase the distance between each AlOOH layer and perform self-consistent calculations until the system energy tends to stabilize. The difference between the energy of this structure and the initial structure yields the exfoliation energy from bulk AlOOH to a single layer. Figure 1 As shown;

[0048] Step S1.2: Cut the AlOOH bulk structure into a single layer, and set the thickness of the vacuum layer to... To eliminate interlayer interactions;

[0049] Step S2: Perform structural optimization calculations on the AlOOH monolayer constructed in Step S1 to obtain a stable structure; determine its ferroelectric spontaneous polarization direction and ferroelastic spontaneous tensile strain direction as along the a-axis. Step S2 includes the following steps:

[0050] Step S2.1: Optimize the atomic positions and unit cell volume of the AlOOH monolayer, setting the parameters to ISIF=3, IBRION=2, and using the conjugate gradient algorithm; the convergence criterion for the force is set to be below 1 / 3 of each atom. The energy convergence criterion is 10. -6 eV;

[0051] Step S2.2: After the convergence criterion is met, proceed to the next step of electronic structure calculation, which shows that AlOOH behaves as a semiconductor, such as... Figure 2 As shown;

[0052] Step S2.3: Ab initio molecular dynamics simulations (AIMD) of the AlOOH monolayer revealed that the system energy did not fluctuate significantly over time, and the structure did not undergo bond breaking or phase transition. Figure 3 As shown, this demonstrates the structure's good thermodynamic stability; furthermore, calculations of its phonon spectrum reveal no significant imaginary frequencies in the Brillouin zone, as... Figure 4 As shown, this confirms the dynamic stability of the system; finally, its elastic constant satisfies Born's mechanical stability criterion: C 11 >|C 12 |>0 and C 66 >0, confirming that the structure has mechanical stability, and the elastic constants are shown in Table 1;

[0053] Table 1. Elastic constants (N / m) of XOOH (X=Sc,Al) monolayer system

[0054]

[0055] Step S3: By rotating the hydroxyl groups in the AlOOH monolayer and applying in-plane stress, another ferroelectric and ferroelastic phases are identified. Based on the system symmetry, intermediate phases are located, and the inversion energy barriers between the two ferroelectric and ferroelastic phases are calculated respectively. Figure 4 As shown, step S3 includes the following steps:

[0056] Step S3.1: Rotating both hydroxyl groups in the AlOOH monolayer simultaneously by 180° along the c-axis yields another stable ferroelectric phase; rotating only one hydroxyl group yields an antiferroelectric phase. (See reference...) Figure 5 (a) Taking the antiferroelectric phase as the intermediate phase, 15 points were inserted between the antiferroelectric phase and the two ferroelectric phases. The ferroelectric inversion energy barrier was calculated to be 0.076 eV / fu by using the climbing elastic band (CI-NEB) method, as shown in Table 2.

[0057] Table 2. Properties of XOOH (X = Sc, Al) monolayer systems

[0058]

[0059] Table 2 includes the spontaneous polarization P and the energy barrier height E of the ferroelectric reversal of the XOOH (X = Sc, Al) monolayer system. FE (eV / fu), height of the iron ball overturning energy barrier E FA (eV / fu) and reversible ferroelastic strain S FA (%)

[0060] Step S3.2: The ferroelectric polarization value P of the AlOOH monolayer was calculated to be 89.5 pC / m using modern polarization theory based on the Berry phase method, as shown in Table 2;

[0061] Step S3.3: Applying uniaxial tensile strain to the short axis (b-axis) of the initial AlOOH monolayer structure can switch the lattice short axis to the a-axis, thereby generating another stable ferroelastic variant. Based on the symmetry of the AlOOH monolayer structure and the position of the hydroxyl groups in the two ferroelastic variants, the structure in which the hydroxyl groups are arranged along the c-axis is taken as the ciselastic phase. Ten points are inserted between the ciselastic phase and the two ferroelastic phases, and NEB calculations are performed to obtain the ferroelastic flip energy barrier as 2.603 eV / fu, as shown in Table 2.

[0062] Step S3.4: According to the reversible ferroelastic strain formula |a / b-1| × 100%, the reversible ferroelastic strain of the AlOOH monolayer is calculated to be 26.3%; in the formula, a and b represent the lattice constants of the system, respectively. and

[0063] Step S4: Calculate the ferroelectric polarization of the AlOOH monolayer as a function of the ferroelastic transition path, and analyze the intrinsic mechanism of the coupling between the two ferroic properties. Step S4 includes the following steps:

[0064] Step S4.1: Calculate the polarization value of each structure in the ferroelastic reversal path. Observe its changes and find that the polarization value along the a-axis gradually decreases until it reaches 0, reaching the compliant state. Then the direction changes to the b-axis and gradually increases again, such as... Figure 6 As shown;

[0065] Step S4.2: Observe the change of hydroxyl direction in each structure of the ferroelastic flipping path. It is found that the hydroxyl group rotates along the ac plane until it is completely aligned along the c axis, reaching the ciselastic state. Then the direction changes to rotate along the bc plane and finally stops in the bc plane. Thus, the ferroelectric-ferroelastic coupling performance of the two-dimensional multiferroic hydroxide material AlOOH, which is coupled with ferroelectricity and ferroelasticity, can be predicted.

[0066] Example 2

[0067] This embodiment is basically the same as Embodiment 1, except that:

[0068] In this embodiment, a method for designing and predicting two-dimensional multiferroic hydroxide materials is presented. This method utilizes hydroxyl rotation to achieve ferroelasticity and ferroelastic coupling, and screens and predicts two-dimensional multiferroic hydroxide materials with ferroelectric and ferroelastic coupling. The steps are as follows:

[0069] Step S1 involves replacing the A-position element in the structural file obtained in Step S1 of Embodiment 1 with Sc, then using visualization software to cleave and cut it, increasing the thickness of the vacuum layer in the c direction, and using VESTA software to convert the structural file type to .vasp file format. Step S1 includes the following steps:

[0070] Step S1.1: Using bulk ScOOH as the initial structure, gradually increase the distance between each layer of ScOOH and perform self-consistent calculations until the system energy tends to stabilize. The difference between the energy of this structure and the initial structure yields the exfoliation energy from the bulk ScOOH to a single layer. Figure 1 As shown;

[0071] Step S1.2: Cut the ScOOH bulk structure into a single layer, and set the thickness of the vacuum layer to... To hinder interlayer interactions;

[0072] Step S2: Perform structural optimization calculations on the ScOOH monolayer obtained in Step S1 to obtain a stable structure; determine its ferroelectric spontaneous polarization direction and ferroelastic spontaneous tensile strain direction as along the a-axis; Step S2 includes the following steps:

[0073] Step S2.1: Optimize the atomic positions and unit cell volume of the ScOOH monolayer, setting the parameters to ISIF=3, IBRION=2, and using the conjugate gradient algorithm; the convergence criterion for the force is set to be below [value missing] per atom. The energy convergence criterion is 10. -6 eV;

[0074] Step S2.2: After the convergence criterion is met, proceed to the next step of electronic structure calculation, which shows that ScOOH behaves as a semiconductor, such as... Figure 2 As shown;

[0075] Step S2.3: Ab initio molecular dynamics simulations (AIMD) of the ScOOH monolayer revealed that the system energy did not fluctuate significantly over time, and the structure did not undergo bond breaking or phase transition. Figure 3 As shown, this demonstrates the structure's good thermodynamic stability; furthermore, calculations of its phonon spectrum reveal no significant imaginary frequencies in the Brillouin zone, as... Figure 4 As shown, this confirms the dynamic stability of the system; finally, its elastic constant satisfies Born's mechanical stability criterion: C 11 >|C 12 |>0 and C 66>0, confirming that the structure has mechanical stability, and the elastic constants are shown in Table 1;

[0076] Step S3: By rotating the hydroxyl groups in the ScOOH monolayer and applying in-plane stress, another ferroelectric and ferroelastic phases are identified. Based on the system symmetry, intermediate phases are located, and the inversion energy barriers between the two ferroelectric and ferroelastic phases are calculated respectively. Figure 5 As shown; step S3 includes the following steps:

[0077] Step S3.1: Rotating both hydroxyl groups in the ScOOH monolayer simultaneously by 180° along the c-axis yields another stable ferroelectric phase; rotating only one hydroxyl group yields an antiferroelectric phase. (See reference...) Figure 5 (a) Using the antiferroelectric phase as the intermediate phase, 15 points were inserted between the antiferroelectric phase and the two ferroelectric phases. The ferroelectric inversion energy barrier was calculated to be 0.008 eV / fu by using the climbing elastic band (CI-NEB) method, as shown in Table 2.

[0078] Step S3.2: The ferroelectric polarization value P of the ScOOH monolayer was calculated to be 47.6 pC / m using modern polarization theory based on the Berry phase method, as shown in Table 2;

[0079] Step S3.3: Applying uniaxial tensile strain to the short axis (b-axis) of the initial ScOOH monolayer structure can switch the lattice short axis to the a-axis, thereby generating another stable ferroelastic variant. Based on the symmetry of the ScOOH monolayer structure and the position of the hydroxyl groups in the two ferroelastic variants, the structure in which the hydroxyl groups are arranged along the c-axis is taken as the ciselastic phase. Ten points are inserted between the ciselastic phase and the two ferroelastic phases, and NEB calculations are performed to obtain the ferroelastic flip energy barrier as 1.655 eV / fu, as shown in Table 2.

[0080] Step S3.4: Based on the reversible ferroelastic strain formula |a / b-1| × 100%, the reversible ferroelastic strain of the ScOOH monolayer is calculated to be 22.9%; in the formula, a and b represent the lattice constants of the system, respectively. and

[0081] Step S4: Calculate the ferroelectric polarization of the ScOOH monolayer as a function of the ferroelastic transition path, and analyze the intrinsic mechanism of coupling between the two ferroic properties; Step S4 includes the following steps:

[0082] Step S4.1: Calculate the polarization value of each structure in the iron ball reversal path, observe its changes and find that the polarization value along the a axis gradually decreases until it reaches 0, reaching the compliant state, and then the direction changes to the b axis, and gradually increases again;

[0083] Step S4.2: Observe the change of hydroxyl direction in each structure of the ferroelastic flipping path. It is found that the hydroxyl group rotates along the ac plane until it is completely aligned along the c axis, reaching the ciselastic state. Then the direction changes to rotate along the bc plane and finally stops in the bc plane. Thus, the ferroelectric-ferroelastic coupling performance of the two-dimensional multiferroic hydroxide material ScOOH, which is coupled with ferroelectricity and ferroelasticity, can be predicted.

[0084] Example 3

[0085] This embodiment is basically the same as Embodiments 1 and 2, except that:

[0086] In this embodiment, a system for designing and predicting two-dimensional multiferroic hydroxide materials is provided. The system program executes the design and prediction method for two-dimensional multiferroic hydroxide materials described in Embodiment 1 or Embodiment 2, and performs screening and prediction of two-dimensional multiferroic hydroxide materials with ferroelectric and ferroelastic coupling.

[0087] The above embodiment describes a method for predicting the multiferroic properties of novel hydroxides based on first-principles calculations, comprising the following steps: Step S1: Obtaining the crystal structure file of a standard three-dimensional hydroxide XOOH (X = Sc, Al) bulk, cutting it using visualization software and adding a vacuum layer in the c-direction, and converting the structure file type to .vasp file format using VESTA software; Step S2: Performing structural optimization calculations on the constructed hydroxide monolayer system to determine its ferroelectric spontaneous polarization and ferroelastic spontaneous strain directions; Step S3: Searching for other ferroelectric and ferroelastic phases in the system by rotating the hydroxyl groups and applying in-plane stress, finding intermediate phases by interpolating points between the two ferroelectric and ferroelastic phases, and calculating the inversion energy barrier between the two ferroelectric and ferroelastic phases respectively; Step S4: Calculating the change in ferroelectric polarization of the system with the ferroelastic transition path to explain the intrinsic mechanism of the coupling of the two ferroic properties.

[0088] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made based on the spirit and principle of the technical solution of the present invention shall be equivalent substitutions. As long as they meet the purpose of the invention and do not deviate from the technical principle and inventive concept of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A method for designing and predicting two-dimensional multiferroic hydroxide materials, characterized in that, Based on hydroxyl rotation to achieve ferroelastic coupling, the following steps are taken to screen and predict two-dimensional multiferroic hydroxide materials with ferroelectric and ferroelastic coupling: Step S1: Obtain the crystal structure file of a standard three-dimensional hydroxide bulk using a crystal database; perform cleavage and cutting of the three-dimensional hydroxide bulk using visualization software; and increase the thickness of the vacuum layer in the c-direction; use VESTA software to convert the crystal structure file type to .vasp file format to obtain the hydroxide monolayer system. Step S2: Perform first-principles calculations to optimize the structure of the hydroxide monolayer system constructed in step S1 to obtain a stable structure; determine the ferroelectric spontaneous polarization and ferroelastic spontaneous strain directions of the hydroxide monolayer system; Step S3: By rotating the hydroxyl groups in the hydroxide monolayer system and applying in-plane stress, find other ferroelectric and ferroelastic phases in the hydroxide monolayer system. Based on the symmetry of the hydroxide monolayer system, find the intermediate phases respectively, and calculate the flipping energy barriers between the two ferroelectric phases and the two ferroelastic phases respectively. Step S4: Calculate the change of ferroelectric polarization of the hydroxide monolayer system with the ferroelastic transition path, obtain the ferroelectric-ferroelastic coupling relationship, and thus predict the two-dimensional multiferroic hydroxide material with ferroelectric and ferroelastic coupling.

2. The method for designing and predicting two-dimensional multiferroic hydroxide materials according to claim 1, characterized in that: In step one, the chemical formula of the three-dimensional hydroxide is XOOH, where X is at least one of Sc and Al.

3. The design and prediction method for two-dimensional multiferroic hydroxide materials according to claim 1, characterized in that: The steps of step S1 are as follows: Step S1.1: Using the three-dimensional hydroxide bulk obtained from the crystal database as the initial structure, gradually increase the interlayer distance and perform self-consistent calculations until the system energy tends to stabilize. The difference between the energy of this structure and the initial structure can be used to obtain the system exfoliation energy. Step S1.2: Using visualization software, the three-dimensional hydroxide block structure is cut into two-dimensional single layers, and the thickness of the vacuum layer is increased in the c-direction, with the thickness of the vacuum layer set to... To eliminate interlayer interactions; Step S1.3: Using VESTA software, convert the crystal structure file type to .vasp file format to obtain the hydroxide monolayer system.

4. The method for designing and predicting two-dimensional multiferroic hydroxide materials according to claim 1, characterized in that, The steps of step S2 are as follows: Step S2.1: Optimize the atomic positions and cell volume of the hydroxide monolayer system, setting the parameters to ISIF=3, IBRION=2, and using the conjugate gradient algorithm; the force convergence criterion is set to less than 3 for each atom. The energy convergence criterion is 10. -6 eV; Step S2.2: After the convergence criterion is met, proceed to the next step of electronic structure calculation, and it will be found that all systems are semiconductors; Step S2.3: By performing ab initio molecular dynamics simulations (AIMD) on the hydroxide monolayer system, and simultaneously calculating its phonon spectrum and elastic constants, the thermodynamic, kinetic, and mechanical stability of the structure is confirmed.

5. The method for designing and predicting two-dimensional multiferroic hydroxide materials according to claim 1, characterized in that, The steps of step S3 are as follows: Step S3.1: Rotate both hydroxyl groups in the hydroxide monolayer system by 180° along the c-axis to obtain another stable ferroelectric phase; rotate only one hydroxyl group to obtain the antiferroelectric phase; use the antiferroelectric phase as the intermediate phase, insert points between the antiferroelectric phase and the two ferroelectric phases respectively, and calculate the ferroelectric inversion energy barrier by using the climbing elastic band (CI-NEB) method. Step S3.2: Calculate the ferroelectric polarization value P of the system using modern polarization theory based on the Berry phase method; Step S3.3: Apply uniaxial tensile strain to the short axis (b-axis) of the initial ferroelastic variant to switch the short axis of the lattice to the a-axis, thereby generating another stable ferroelastic variant; based on the structural symmetry and the position of the hydroxyl groups in the two ferroelastic variants, take the structure in which the hydroxyl groups are arranged along the c-axis as the ciselastic phase, insert a point between the ciselastic phase and the two ferroelastic phases, perform NEB calculations, and obtain the ferroelastic inversion energy barrier; Step S3.4: Calculate the reversible ferroelastic strain of the system according to the reversible ferroelastic strain formula |a / b-1|×100%, where a and b represent the lattice constants of the system.

6. The method for designing and predicting two-dimensional multiferroic hydroxide materials according to claim 1, characterized in that, The steps of step S4 are as follows: Step S4.1: Calculate the polarization value of each structure in the iron ball's flipping path and observe its changes; Step S4.2: Observe the change in the hydroxyl direction in each structure of the ferroelastic flipping path; thereby predicting the ferroelectric-ferroelastic coupling performance of the two-dimensional multiferroic hydroxide material coupled with ferroelectricity and ferroelasticity.

7. A system for the design and prediction of two-dimensional multiferroic hydroxide materials, characterized in that, Its system program executes the design and prediction method for two-dimensional multiferroic hydroxide materials as described in claim 1, and performs screening and prediction of two-dimensional multiferroic hydroxide materials with ferroelectric and ferroelastic coupling.

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