A first-principles calculation method for studying the structural properties of clusters in sodium tungstate molten salt system

Abstract

The present invention provides a first-principles calculation method for studying the cluster structure properties of a sodium tungstate molten salt system, the first-principles calculation method comprising: constructing a basic structure model with W atoms, O atoms and molten salt system anions, gradually replacing the molten salt system anions with O atoms to obtain cluster structures before and after the replacement, optimizing the cluster structure, and evaluating the actual stability of the convergent structure obtained after the structural optimization through bond length and binding energy. The method can be used to explore the reaction mechanism and existence form of tungsten ion clusters in molten salts through first-principles calculations, reduce the complexity of experimental screening operations, greatly reduce the expenditure of manpower and material resources of traditional experimental methods, shorten the research and development cycle of new materials, and has high application value.

Description

Technical Field

[0001] The invention relates to the technical field of computational material chemistry, and in particular to a first-principles calculation method for studying the structural properties of clusters of a sodium tungstate molten salt system. Background Art

[0002] As an important non-renewable rare strategic resource, tungsten is widely used in metal processing, mining and stone cutting tools, electronic optical materials, armaments and aerospace, new functional materials and other fields due to its high melting point, strong corrosion resistance, high density and good thermal conductivity.

[0003] At present, the production processes of tungsten powder include self-propagating high-temperature reduction method, spray drying-fluidized bed method, tungstate direct reduction method, tungsten oxide reduction method, tungsten halide hydrogen reduction method, molten salt electrolysis method and high-energy ball milling method. Among them, the use of molten salt electrolysis technology to extract metallic tungsten has received widespread attention for a long time. In the 1960s and 1970s, tungsten powder was extracted by electrolyzing tungsten oxides such as sodium tungstate, tungsten oxide, and calcium tungstate using sodium phosphate-sodium borate and chloride-fluoride as electrolyte systems. Among them, sodium tungstate is the most commonly used because of its low price and easy availability. As the most commonly used tungsten oxide electrolyte in tungsten electrolysis, people have never stopped studying the structure and properties of sodium tungstate.

[0004] However, due to the limitation of experimental conditions, the properties and action mechanism of molten salt electrolyte system are difficult to obtain through experiments, especially the coordination form of tungsten in chloride and fluoride molten salts. In recent years, with the gradual development of computational chemistry, the use of computational simulation methods to study the structure and properties of substances has been recognized by more and more people. Therefore, the present invention aims to provide a first-principles calculation method for studying the structural properties of clusters in sodium tungstate molten salt system. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a first-principles calculation method for studying the cluster structure properties of a sodium tungstate molten salt system.

[0006] The present invention adopts the following technical solutions:

[0007] The present invention provides a first-principles calculation method for studying the cluster structure properties of a sodium tungstate molten salt system, comprising:

[0008] A basic structural model was constructed with W atoms, O atoms and molten salt system anions. O atoms were gradually used to replace the molten salt system anions to obtain the cluster structures before and after the replacement. The cluster structure was optimized, and the actual stability of the converged structure obtained after the structural optimization was evaluated by bond length and binding energy.

[0009] The most important thing in the first-principles calculation process is to find a suitable basic model and construction method. Through extensive research, the present invention has discovered a simple and effective model construction method suitable for the coordination morphology of tungsten ion clusters in molten salt electrolysis systems, and screened out stable tungsten ion cluster coordination configurations to be suitable for different tungsten electrolysis molten salt systems, providing effective guidance for tungsten electrolysis production.

[0010] Further, when the sodium tungstate molten salt system is a chloride-sodium tungstate molten salt system, the basic structure model is W a O x+a-1 Cl y Structural model.

[0011] In a preferred embodiment of the present invention, the calculation method comprises the following steps:

[0012] (1) With W a O x+a-1 Cl y Based on the structural model, a mathematical model is constructed;

[0013] (2) Using mathematical models and constraints, the number of oxygen atoms is fixed, and the number of chlorine atoms and the single and double bonds of tungsten oxygen are gradually determined, thereby exhaustively enumerating possible cluster structures;

[0014] (3) optimizing the cluster structure obtained in step (2) and completing structural relaxation;

[0015] (4) The actual stability of the converged structure obtained after structural optimization is evaluated through bond length and binding energy.

[0016] Among them, in step (2), the constraint conditions include: setting n x Indicates the single and double bonds of tungsten oxygen, 1≤n x ≤2, where n x =1, all tungsten and oxygen are single bonds, n x =2, there are double bonds between tungsten and oxygen, n x Between 1 and 2, there are both single bonds and double bonds between tungsten and oxygen.

[0017] Furthermore, the constraint condition also includes: 6a-2(x+a-1)-y<0, xn x +y=4a+2.

[0018] In step (2), cluster structure models with different numbers of W atoms are constructed using 3D modeling software Materials Studio or VESTA.

[0019] In step (3), the cluster structure obtained in step (2) is structurally optimized using the first-principles VASP or Dmol3 calculation module, and structures that can converge after structural relaxation are preliminarily screened out.

[0020] Further, when the sodium tungstate molten salt system is a fluoride-sodium tungstate molten salt system, the basic structure model is W a O x+a-1 F y Structural model. The calculation under this molten salt system can refer to the calculation method of chloride-sodium tungstate molten salt system.

[0021] In a preferred embodiment of the present invention, the calculation method comprises the following steps:

[0022] (1) With W a O x+a-1 F y Based on the structural model, a mathematical model is constructed;

[0023] (2) Using mathematical models and constraints, the number of oxygen atoms is fixed, and the number of fluorine atoms and the single and double bonds of tungsten and oxygen are gradually determined, thereby exhaustively enumerating possible cluster structures;

[0024] (3) optimizing the cluster structure obtained in step (2) and completing structural relaxation;

[0025] (4) The actual stability of the converged structure obtained after structural optimization is evaluated through bond length and binding energy.

[0026] Further, when the sodium tungstate molten salt system is a chloride-fluoride-sodium tungstate molten salt system, the basic structure model is W a O x+a-1 F y-z Cl z Structural model. The calculation under this molten salt system can refer to the calculation method of the chloride-sodium tungstate molten salt system, and F and Cl are taken as a whole, which is equivalent to Cl in the chloride-sodium tungstate molten salt system, and its constraints are still applicable.

[0027] The present invention provides a first-principles calculation method for studying the cluster structure properties of sodium tungstate molten salt system. The method can be used to explore the reaction mechanism and existence form of tungsten ion clusters in molten salt through first-principles calculation, reduce the complexity of experimental screening operations, greatly reduce the expenditure of manpower and material resources of traditional experimental methods, shorten the research and development cycle of new materials, and has high application value. The method can be applied not only to sodium tungstate molten salt system, but also to cluster configuration speculation of other similar molten salt systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 WO4 obtained in the embodiment of the present invention2- , W2O7 2- ,W3O 10 2- Schematic diagram of the structure. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment provides a first-principles calculation method for studying the cluster structure properties of a sodium tungstate molten salt system, comprising the following steps:

[0032] S1, WO x Cl y Based on the structural model, a mathematical model is constructed, and each configuration is taken into account through exhaustive method. According to the structural model and the basic properties of the material, constraints are set: Assume that n x Indicates the single and double bonds of tungsten oxygen, 1≤n x ≤2(n x =1, all tungsten and oxygen are single bonds, n x =2, there are double bonds between tungsten and oxygen, n x When it is between 1 and 2, there are both single bonds and double bonds between tungsten and oxygen, then 6-2x-y<0, xn x +y=6; where x can take values ​​of: 0, 1, 2, 3, 4, 5, 6; y can take values ​​of: 0, 1, 2, 3, 4, 5, 6.

[0033] S2. Using mathematical models and constraints, fix the number of oxygen atoms and gradually determine the number of chlorine atoms and the single and double bonds of tungsten oxygen:

[0034] When x=0, y>6, which does not conform to the actual situation and is discarded;

[0035] When x=1, y>4, then 1≤xn x ≤2, divided into 1 single bond O or 1 double bond O case;

[0036] When x=2, y>2, then 2≤xn x ≤4, divided into 2 single bond O or 2 double bond O or 1 double bond and 1 single bond O;

[0037] When x=3, y>0, then 3≤xn x≤6, divided into 3 single bonds O or 1 double bond 2 single bonds O or 2 double bonds 1 single bond O;

[0038] When x=4, y>-2, then 4≤xn x ≤8, divided into 4 single bonds O or 1 double bond 3 single bonds O or 2 double bonds 2 single bonds O;

[0039] ... and so on, and use the 3D modeling software Materials Studio or VESTA to construct a tungsten ion cluster structure model of a W atom in the above situation.

[0040] S3. Use the first-principles VASP or Dmol3 calculation module to optimize the new structure constructed above and complete structural relaxation.

[0041] S4. Evaluate the actual stability of the converged structure obtained after structural optimization through bond length and binding energy, and preliminarily screen out the structures that can converge after structural relaxation.

[0042] Example 2

[0043] This embodiment provides a first-principles calculation method for studying the cluster structure properties of a sodium tungstate molten salt system, comprising the following steps:

[0044] S1, W2O x+1 Cl y Based on the structural model, a mathematical model is constructed, and each configuration is taken into account through exhaustive method. According to the structural model and the basic properties of the material, constraints are set: Assume that n x Indicates the single and double bonds of tungsten oxygen, 1≤n x ≤2(n x =1, all tungsten and oxygen are single bonds, n x =2, there are double bonds between tungsten and oxygen, n x When it is between 1 and 2, there are both single bonds and double bonds between tungsten and oxygen, then 10-2x-y<0, xn x +y=10 (since two Ws cannot be directly connected, WOW must exist in the configuration, and only the other 10 empty orbital states need to be constrained); where x can take values ​​of: 0, 1, 2, 3, ..., 10; y can take values ​​of: 0, 1, 2, 3, ..., 10.

[0045] S2. Using mathematical models and constraints, fix the number of oxygen atoms and gradually determine the number of chlorine atoms and the single and double bonds of tungsten oxygen:

[0046] When x=0, y>10, which does not conform to the actual situation, it is discarded;

[0047] When x=1, y>8, then 1≤xnx ≤2, divided into 1 single bond O or 1 double bond O case;

[0048] When x=2, y>6, then 2≤xn x ≤4, divided into 2 single bond O or 2 double bond O or 1 double bond and 1 single bond O;

[0049] When x=3, y>4, then 3≤xn x ≤6, divided into 3 single bonds O or 1 double bond 2 single bonds O or 2 double bonds 1 single bond O;

[0050] ... and so on, and use the 3D modeling software Materials Studio or VESTA to construct a tungsten ion cluster structure model of the two W atoms in the above case.

[0051] S3. Use the first-principles VASP or Dmol3 calculation module to optimize the new structure constructed above and complete structural relaxation.

[0052] S4. Evaluate the actual stability of the converged structure obtained after structural optimization through bond length and binding energy, and preliminarily screen out the structures that can converge after structural relaxation.

[0053] Example 3

[0054] This embodiment provides a first-principles calculation method for studying the cluster structure properties of a sodium tungstate molten salt system, comprising the following steps:

[0055] S1, W3O x+2 Cl y Based on the structural model, a mathematical model is constructed, and each configuration is taken into account through exhaustive method. According to the structural model and the basic properties of the material, constraints are set: Assume that n x Indicates the single and double bonds of tungsten oxygen, 1≤n x ≤2(n x =1, all tungsten and oxygen are single bonds, n x =2, there are double bonds between tungsten and oxygen, n x When it is between 1 and 2, there are both single bonds and double bonds between tungsten and oxygen, then 14-2x-y<0, xn x +y=14(WOWOW exists in the configuration, and we only need to consider the bonding of the remaining x Os); where x can be 0, 1, 2, 3, ..., 14; y can be 0, 1, 2, 3, ..., 14.

[0056] S2. Using mathematical models and constraints, fix the number of oxygen atoms and gradually determine the number of chlorine atoms and the single and double bonds of tungsten oxygen:

[0057] When x=0, y>14, which does not conform to the actual situation and is discarded;

[0058] When x=1, y>12, then 1≤xn x ≤2, divided into 1 single bond O or 1 double bond O case;

[0059] When x=2, y>10, then 2≤xn x ≤4, divided into 2 single bond O or 2 double bond O or 1 double bond and 1 single bond O;

[0060] When x=3, y>8, then 3≤xn x ≤6, divided into 3 single bonds O or 1 double bond 2 single bonds O or 2 double bonds 1 single bond O;

[0061] ... and so on, and use the 3D modeling software Materials Studio or VESTA to construct a tungsten ion cluster structure model of three W atoms in the above case.

[0062] S3. Use the first-principles VASP or Dmol3 calculation module to optimize the new structure constructed above and complete structural relaxation.

[0063] S4. Evaluate the actual stability of the converged structure obtained after structural optimization through bond length and binding energy, and preliminarily screen out the structures that can converge after structural relaxation.

[0064] By evaluating the structural stability and binding energy of tungsten ion clusters constructed based on different numbers of W atoms, it was found that WO4 2- , W2O7 2- ,W3O 10 2- The structure (such as Figure 1 The binding energy increases with the number of W atoms, as shown in Table 1.

[0065] Table 1 Bond lengths and binding energies of stable structures

[0066]

[0067] This conclusion is consistent with the experimental data recognized by the public, proving the rationality and reliability of the method of the present invention. The screening method of the present invention can quickly screen out a structurally stable tungsten ion cluster structure model, which is of great significance for the exploration of the molten salt electrolyte mechanism and the existence form of ions. At the same time, the results can also be extended to the study of ion coordination forms in other molten salt systems, proving that the complex coordination structure of multi-element high-valent ions such as WO-Cl is relatively less stable than the coordination structure of single-element high-valent ions such as WO.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A first-principles calculation method for studying the cluster structure properties of sodium tungstate molten salt system, characterized in that: include: A basic structure model is constructed with W atoms, O atoms and molten salt system anions, O atoms are gradually substituted for molten salt system anions to obtain cluster structures before and after the substitution, the cluster structure is structurally optimized, and the actual stability of the convergent structure obtained after the structural optimization is evaluated through bond length and binding energy; The sodium tungstate molten salt system is a chloride-sodium tungstate molten salt system, and the basic structure model is W a O x+a-1 Cl y Structural model; The calculation method comprises the following steps: (1) With W a O x+a-1 Cl y Based on the structural model, a mathematical model is constructed; (2) Using mathematical models and constraints, the number of oxygen atoms is fixed, and the number of chlorine atoms and the single and double bonds of tungsten oxygen are gradually determined, thereby exhaustively enumerating possible cluster structures; (3) optimizing the cluster structure obtained in step (2) and completing structural relaxation; (4) Evaluate the actual stability of the converged structure obtained after structural optimization through bond length and binding energy; In step (2), the constraints include: setting n x Indicates the single and double bonds of tungsten oxygen, 1≤n x ≤2, where n x =1, all tungsten and oxygen are single bonds, n x =2, there are double bonds between tungsten and oxygen, n x When it is between 1 and 2, there are both single bonds and double bonds between tungsten and oxygen; the constraint conditions also include: 6a-2(x+a-1)-y<0, xn x +y=4a+2; Where a is a positive integer, x is 0 or a positive integer, and y is 0 or a positive integer.

2. The first principles calculation method for studying the cluster structure properties of the sodium tungstate molten salt system according to claim 1 is characterized in that: In step (2), cluster structure models with different numbers of W atoms are constructed using 3D modeling software Materials Studio or VESTA.

3. The first principles calculation method for studying the cluster structure properties of the sodium tungstate molten salt system according to claim 1 is characterized in that: In step (3), the cluster structure obtained in step (2) is structurally optimized using the first-principles VASP or Dmol3 calculation module, and structures that can converge after structural relaxation are preliminarily screened out.

4. The first principles calculation method for studying the cluster structure properties of the sodium tungstate molten salt system according to claim 1 is characterized in that: The sodium tungstate molten salt system is a fluoride-sodium tungstate molten salt system, and the basic structure model is W a O x+a-1 F y Structural model.

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