Molecular dynamics simulation method for quantifying Van der Waals force action intensity between molecules

Abstract

The invention relates to the technical field of molecular dynamics simulation, and discloses a molecular dynamics simulation method for quantifying Van der Waals force action intensity among molecules, which comprises the following steps: constructing an initial system model based on molecular dynamics simulation software, grouping target components, and carrying out molecular dynamics simulation. Energy change conditions among target components and distance change conditions among target molecules are recorded at any time, and finally, Van der Waals force action intensity is calculated by combining a Van der Waals force calculation formula. According to the method, the Van der Waals force action intensity between two different components can be quickly and accurately quantified, the microscopic action mechanism between the components is defined, and a theoretical basis is provided for deep learning of interaction between molecules.

Description

Technical Field

[0001] This application relates to the technical field of molecular dynamics simulation, and particularly to a molecular dynamics simulation method for quantifying the interaction strength of van der Waals forces between molecules. Background Art

[0002] As an important microscopic intermolecular force, van der Waals force widely exists within molecules. It affects the interaction between multiphase fluids, thereby influencing the flow ability of fluids and the adsorption ability of fluids on the pore surface. Therefore, quantifying the interaction strength of van der Waals forces between different components helps to clarify the microscopic interaction mechanism between multiphase fluids.

[0003] Currently, the main experimental methods for measuring van der Waals forces include the surface force apparatus method, the atomic force microscopy method, etc. However, the surface force apparatus method is more suitable for measuring the van der Waals force between surfaces, and the influence of capillary force is relatively large, which limits its application scope. The measurement efficiency of the atomic force microscopy imaging method is low and it is easy to damage the surface to be measured. In addition, experimental methods are limited by experimental temperature and pressure conditions, and experimental methods are costly and time-consuming, with certain errors.

[0004] Molecular dynamics simulation technology can, to a certain extent, make up for the deficiencies of experimental research. It can simulate the intermolecular interaction process from a microscopic perspective and provide detailed information on the evolution of the interaction energy over time, so as to comprehensively understand the action mechanism of van der Waals forces. Therefore, the present invention provides a molecular dynamics simulation method for quantifying the interaction strength of van der Waals forces between molecules. Summary of the Invention

[0005] The purpose of this application is to provide a molecular dynamics simulation method for quantifying the interaction strength of van der Waals forces between molecules. An initial system model is constructed based on molecular dynamics simulation software, and the molecular dynamics simulation process is carried out and the energy changes between molecules during the simulation process are statistically analyzed. Combining the orientation force calculation formula, the induction force calculation formula, the dispersion force calculation formula, and the van der Waals force calculation formula to clarify the interaction strength of van der Waals forces between molecules, laying a foundation for clarifying the microscopic interaction mechanism between oil and gas components.

[0006] In order to achieve the above purpose, the following technical solutions are adopted:

[0007] This application provides a molecular dynamics simulation method for quantifying the interaction strength of van der Waals forces between molecules, and the method includes:

[0008] Construct an initial system model; wherein, the initial system model is composed of a plurality of single-component models combined;

[0009] Group the target components in the initial system model and perform molecular dynamics simulation;

[0010] Obtain the energy change and molecular distance change between each target component during the simulation process;

[0011] Calculate the van der Waals force intensity according to the energy change and molecular distance change between each target component.

[0012] Furthermore, construct an initial system model, including:

[0013] Construct multiple single-component models, and assign force field and charge parameters to each element in the single-component models to ensure that the total charge in the initial system model is electrically neutral;

[0014] Combine each single-component model to form an initial system model according to the simulation requirements.

[0015] Furthermore, after grouping the target components in the initial system model, perform molecular dynamics simulation through the following method:

[0016] Use the conjugate gradient algorithm to minimize the energy of the model so that the atoms in the model are in a stable state;

[0017] Assign a temperature to the target components and apply an ensemble command to make the target components have initial kinetic energy, thereby starting the molecular dynamics simulation process.

[0018] Furthermore, use the orientation force, induction force, and / or dispersion force to characterize the energy change and molecular distance change between each target component during the simulation process.

[0019] Furthermore, due to the fixed distribution of charges inside polar molecules, there are inherent electrodes inside the molecules. When polar molecules approach each other, the molecular repulsive force between like charges and the molecular attractive force between opposite charges will generate an orientation force through the orientation effect between molecular dipoles; the calculation formula for the orientation force is as follows:

[0020]

[0021] In the formula: E μiμj represents the orientation force effect between two molecules; r represents the centroid distance of the target molecule; μ i , μ j represent the dipole moments of two molecules; ε 0 represents the vacuum permittivity; k represents the Boltzmann constant, 1.38×10 -23 ; T represents the thermodynamic temperature.

[0022] Furthermore, due to the permanent dipole effect of the fixed charge distribution inside polar molecules, when a polar molecule approaches a non-polar molecule, the charge distribution inside the polar molecule will induce the offset of positive and negative charges inside the non-polar molecule, resulting in the non-coincidence of the centers of gravity of positive and negative charges inside the non-polar molecule, and the relative displacement of charges to generate an induced dipole effect. The mutual force generated between instantaneous dipoles is called the induction force; the calculation formula of the induction force is as follows:

[0023]

[0024] In the formula: E μiαj represents the induction force between two molecules; μ i represents the dipole moment inside the polar molecule; α j represents the polarizability between non-polar molecules; ε 0 represents the permittivity of vacuum; r represents the distance between the centers of mass of the target molecules.

[0025] Furthermore, when non-polar molecules approach each other, due to the migration of charges inside the molecules and the continuous vibration of atomic nuclei, the instantaneous relative displacement of the electron cloud and atomic nuclei inside the molecules often occurs, thus generating instantaneous dipoles. The mutual force generated between instantaneous dipoles is called the dispersion force; the calculation formula of the dispersion force is as follows:

[0026]

[0027] In the formula: E αiαj represents the dispersion force between two molecules; I i 、I j represent the ionization energies of the two molecules; α i 、α j represent the polarizabilities of the two molecules; ε 0 represents the permittivity of vacuum; r represents the distance between the centers of mass of the target molecules.

[0028] Furthermore, the van der Waals force is often used to describe the mutual force caused by permanent dipoles and instantaneous dipoles between molecules, mainly including the orientation force, the induction force, and the dispersion force; the calculation formula of the van der Waals force is as follows:

[0029]

[0030] In the formula: E vdw represents the van der Waals force between molecules; ε represents the depth of the potential well; r represents the distance between the centers of mass of the molecules; i, j represent different atoms; ε ij represents the LJ well depth between atoms i and j; r 0 ij represents the distance between atoms i and j at equilibrium; r ij represents the distance between atoms i and j.

[0031] The beneficial effects of this application are as follows:

[0032] This application uses the molecular dynamics simulation method to construct a target system model and carry out the molecular dynamics simulation process. By combining the orientation force, induction force, and dispersion force, the calculation formula of the van der Waals force is further clarified, thereby quantifying the strength of the van der Waals force interaction between molecules and providing theoretical guidance for the efficient development of oil reservoirs. Description of the Drawings

[0033] Figure 1 It is a flowchart of a molecular dynamics simulation method for quantifying the strength of the van der Waals force between molecules provided by an embodiment of this application;

[0034] Figure 2 It is a model diagram of the CO 2 component provided by an embodiment of this application;

[0035] Figure 3 It is a single-chain model diagram of the crude oil C 12 H 26 provided by an embodiment of this application;

[0036] Figure 4 It is a model diagram of the hydroxylated quartz wall surface provided by an embodiment of this application;

[0037] Figure 5 It is a model diagram of the displacement system provided by an embodiment of this application;

[0038] Figure 6 It is a curve of the change in the strength of the van der Waals force between oil and gas during the CO 2 displacement process provided by an embodiment of this application;

[0039] Figure 7 It is a single-chain model diagram of the crude oil C 8 H 18 provided by an embodiment of this application;

[0040] Figure 8 It is a model diagram of the methylated quartz wall surface provided by an embodiment of this application;

[0041] Figure 9 It is a model diagram of the oil-gas competitive adsorption provided by an embodiment of this application;

[0042] Figure 10 It is a curve of the change in the strength of the van der Waals force between CO 2 , crude oil and the methylated wall surface during the oil-gas competitive adsorption process provided by an embodiment of this application. Detailed Embodiments

[0043] The following describes the implementation manners of the present application through specific specific examples. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification. The present application can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0044] The following further describes in detail the specific implementation manners of the present application in conjunction with the accompanying drawings and embodiments.

[0045] Embodiment 1:

[0046] Please refer to Figure 1 , which is a flowchart of a molecular dynamics simulation method for quantifying the interaction strength of intermolecular van der Waals forces provided by an embodiment of the present application. An embodiment of the present application provides a molecular dynamics simulation method for quantifying the interaction strength of intermolecular van der Waals forces. In this embodiment, taking the interaction strength of the van der Waals forces between crude oil and CO 2 molecules during the process of CO 2 displacing crude oil as an example, it can be implemented through the following steps S1 to S11.

[0047] S1. Construct an initial system model of CO 2 displacing crude oil through molecular dynamics simulation software.

[0048] First, construct models of CO 2 , crude oil, and pore models respectively. Among them, C 12 H 26 is used as the crude oil component, and hydroxyl quartz is used as the pore model. The single models of CO 2 , crude oil, and hydrophilic quartz are as shown in Figure 2 , Figure 3 , Figure 4 .

[0049] S2. Assign appropriate force fields to the elements in each component model and apply charges to ensure that the total charge number of each component model is in an electrically neutral state.

[0050] S3. Combine each single component in sequence to form an initial displacement system model.

[0051] As shown in Figure 5 ; after the initial model is constructed, the components in the model are grouped to facilitate subsequent application of initial kinetic energy to the target components to carry out molecular dynamics simulation and quantitative characterization of related physical quantities.

[0052] S4. Use the conjugate gradient algorithm to carry out an energy minimization process on the model to make the atoms in the model in a stable state;

[0053] S5. Conduct the molecular dynamics simulation process at a temperature of 353K and under the NVT (canonical) ensemble conditions.

[0054] S6. During the simulation process, statistically record the total energy change of the model system in real time, especially record the change in the interaction energy between crude oil and CO 2 components.

[0055] S7. Due to the fixed charge distribution inside polar molecules, there are inherent electrodes inside the molecules. When polar molecules approach each other, the molecular repulsive force between like charges and the molecular attractive force between opposite charges will generate an orientation force through the orientation effect between molecular dipoles; the calculation formula for the orientation force is as follows:

[0056]

[0057] In the formula: E μiμj represents the orientation force interaction between two molecules; r represents the centroid distance of the target molecule; μ i , μ j represent the dipole moments of two molecules; ε 0 represents the vacuum permittivity; k represents the Boltzmann constant, 1.38×10 -23 ; T represents the thermodynamic temperature.

[0058] S8. Due to the permanent dipole effect of the fixed charge distribution inside polar molecules, when a polar molecule approaches a non-polar molecule, the charge distribution inside the polar molecule will induce the offset of positive and negative charges inside the non-polar molecule, resulting in the non-coincidence of the centers of gravity of positive and negative charges inside the non-polar molecule, and the relative displacement of charges to generate an induced dipole effect. The mutual force generated between instantaneous dipoles is called the induction force; the calculation formula for the induction force is as follows:

[0059]

[0060] In the formula: E μiαj represents the induction force interaction between two molecules; μ i represents the dipole moment inside the polar molecule; α j represents the polarizability between non-polar molecules; ε 0 represents the vacuum permittivity; r represents the centroid distance of the target molecule.

[0061] S9. When non-polar molecules approach each other, due to the migration of charges inside the molecules and the continuous vibration of atomic nuclei, the instantaneous relative displacement of the electron cloud and atomic nucleus inside the molecule often occurs, thus generating an instantaneous dipole. The mutual force generated between instantaneous dipoles is called the dispersion force; the calculation formula for the dispersion force is as follows:

[0062]

[0063] Where: E αiαj Represents the dispersion force between two molecules; I i ,I j represents the ionization energy of the two molecules; α i , α j represents the polarizability of the two molecules; ε 0 represents the vacuum permittivity; r represents the distance from the center of mass of the target molecule.

[0064] S10. Van der Waals force is often used to describe the interaction force caused by permanent dipole and instantaneous dipole between molecules, which mainly includes orientation force, induction force and dispersion force. The calculation formula of van der Waals force is as follows:

[0065]

[0066] Where: E vdw represents the van der Waals force between molecules; ε represents the potential well depth; r represents the center of mass distance between molecules; i and j represent different atoms.

[0067] S11, by combining the above molecular interaction force calculation formula to obtain CO 2 The strength of the van der Waals forces between oil and gas molecules during oil displacement.

[0068] like Figure 6 As shown in Figure 2, the van der Waals interaction energy between oil and gas increases with the increase of simulation time, indicating that as CO 2 The molecules enter the pores and gradually disperse the aggregated crude oil molecules. The van der Waals interaction between oil and gas molecules is enhanced, and the degree of mutual solubility of oil and gas increases.

[0069] Embodiment 2:

[0070] See also Figure 1 , is a flow chart of a molecular dynamics simulation method for quantifying the strength of van der Waals forces between molecules provided in an embodiment of the present application. This embodiment of the present application provides a molecular dynamics simulation method for quantifying the strength of van der Waals forces between molecules. In this embodiment, the CO 2 In the process of competing with crude oil for adsorption, crude oil, CO 2 The strength of the van der Waals force interaction between molecules and the wall is used as an example to clarify the role of the van der Waals force in the competitive adsorption process, which is specifically implemented through the following steps S1 to S10.

[0071] S1. Constructing CO using molecular dynamics simulation software 2 Initial system model for displacing crude oil.

[0072] First, construct CO2 , crude oil, pore model, in which C 8 H 18 is used as a crude oil component, and the pore model is composed of methylated quartz. A single model is as shown in Figure 7 , Figure 8 ; In this process, appropriate force fields and charge parameters are assigned to each element in the component model to ensure that the total charge number of each model is in an electrically neutral state.

[0073] S2. Combine each single component in sequence to form a displacement initial system model.

[0074] As shown in Figure 9 ; After the initial model is constructed, the components in the model are grouped to facilitate subsequent kinetic simulations of the target components and quantification of relevant physical quantities.

[0075] S3. Use the conjugate gradient algorithm to carry out an energy minimization process on the model to make the atoms in the model in a stable state.

[0076] S4. Carry out a molecular dynamics simulation process under the conditions of a temperature of 353K and an NVT (canonical) ensemble.

[0077] S5. During the simulation process, the total energy change of the model system is statistically recorded in real time, especially recording the change in the interaction energy between CO 2 , crude oil and the methylated quartz wall.

[0078] S6. During the simulation process, due to the inherent dipole between polar molecules, when the target polar molecules approach each other, due to the repulsive force between like poles and the attractive force between opposite poles, the molecules will undergo relative displacement. This force generated by the dipole orientation effect is called the orientation force; the calculation formula for the orientation force is as follows:

[0079]

[0080] In the formula: E μiμj represents the orientation force interaction between two molecules; r represents the centroid distance of the target molecule; μ i , μ j represent the dipole moments of two molecules; ε 0 represents the vacuum permittivity; k represents the Boltzmann constant, 1.38×10 -23 ; T represents the thermodynamic temperature.

[0081] S7. During the simulation process, when a non-polar molecule approaches a polar molecule, a phenomenon of relative displacement of the positive and negative charge centers will occur inside the non-polar molecule, thus further generating an induced dipole. Therefore, the mutual force generated between the instantaneous dipoles is called the induced force; the calculation formula for the induced force is as follows:

[0082]

[0083] In the formula: E μiαj represents the induction force between two molecules; μ i represents the dipole moment inside the polar molecule; α j represents the polarizability between non-polar molecules; ε 0 represents the permittivity of vacuum; r represents the centroid distance of the target molecule.

[0084] S8. During the simulation process, when two non-polar molecules approach each other, the movement of electrons and the vibration of atomic nuclei will further cause the relative displacement between the electron cloud and the atomic nuclei, thus generating an instantaneous dipole. The mutual force generated by the instantaneous dipoles is called the dispersion force; the calculation formula of the dispersion force is as follows:

[0085]

[0086] In the formula: E αiαj represents the dispersion force between two molecules; I i , I j represent the ionization energies of the two molecules; α i , α j represent the polarizabilities of the two molecules; ε 0 represents the permittivity of vacuum; r represents the centroid distance of the target molecule.

[0087] S9. The van der Waals force is often used to describe the mutual force caused by the permanent dipole and instantaneous dipole between molecules, mainly including the orientation force, the induction force, and the dispersion force; the calculation formula of the van der Waals force is as follows:

[0088]

[0089] In the formula: E vdw represents the van der Waals force between molecules; ε represents the depth of the potential well; r represents the centroid distance between molecules; i, j represent different atoms.

[0090] S10. By combining the above calculation formulas of the intermolecular interaction forces, the van der Waals force intensity between CO 2 , crude oil and the methylated wall surface during the oil-gas competitive adsorption process is obtained.

[0091] As Figure 10 shown. During the oil-gas competitive adsorption process, the van der Waals force between CO 2 and the wall surface gradually increases, and the van der Waals force between the crude oil and the wall surface gradually decreases, indicating that as the competitive adsorption proceeds, CO 2 gradually strips and displaces the crude oil molecules in the near-wall region and occupies the adsorption sites on the pore surface, thus resulting in CO2 - The van der Waals interaction between the walls is enhanced, and the van der Waals interaction between the crude oil and the walls is weakened.

[0092] The above embodiments are only used to illustrate the present application and are not intended to limit the present application. Those of ordinary skill in the relevant technical field can also make various changes and modifications without departing from the spirit and scope of the present application. Therefore, all equivalent technical solutions also belong to the scope of the present application, and the patent protection scope of the present application shall be defined by the claims.

Claims

1. A molecular dynamics simulation method for quantifying the strength of intermolecular van der Waals forces, characterized in that: The method comprises: Constructing an initial system model; wherein the initial system model is composed of a plurality of single component models; Grouping the target components in the initial system model and performing molecular dynamics simulation; Obtain the energy changes and molecular distance changes between target components during the simulation; The strength of the van der Waals force is calculated based on the energy changes and molecular distance changes between the target components.

2. The molecular dynamics simulation method for quantifying the strength of intermolecular van der Waals forces according to claim 1, characterized in that: Construct an initial system model, including: Constructing multiple single-component models, and assigning force field and charge parameters to each element in the single-component model to ensure that the total charge in the initial system model is in an electrically neutral state; According to the simulation requirements, the single component models are combined to form an initial system model.

3. The molecular dynamics simulation method for quantifying the strength of intermolecular van der Waals forces according to claim 2, characterized in that: After the target components in the initial system model are grouped, molecular dynamics simulation is performed by the following method: The conjugate gradient algorithm is used to minimize the energy of the model so that the atoms in the model are in a stable state; The target component is given a temperature and an ensemble command is applied to give the target component an initial kinetic energy, thereby carrying out a molecular dynamics simulation process.

4. The molecular dynamics simulation method for quantifying the strength of intermolecular van der Waals forces according to claim 1, characterized in that: Orientation forces, induction forces and / or dispersion forces are used to characterize the energy changes and molecular distance changes between target components during the simulation process.

5. The molecular dynamics simulation method for quantifying the strength of intermolecular van der Waals forces according to claim 4, characterized in that: The target components include polar molecules and non-polar molecules. The charges inside the polar molecules are fixedly distributed, the polar molecules contain inherent electrodes, and the non-polar molecules are fixedly distributed inside and have permanent dipole effects.

6. The molecular dynamics simulation method for quantifying the strength of intermolecular van der Waals forces according to claim 5, characterized in that: When polar molecules approach each other, the molecular repulsion between the same-level charges and the molecular attraction between the opposite-polar charges generate an orientation force through the orientation effect between the molecular dipoles. The orientation force calculation formula is as follows: Where: E μiμj represents the orientation force between two polar molecules; r represents the distance from the center of mass of the target molecule; μ i , μ j represents the dipole moment of two polar molecules; ε0 represents the vacuum permittivity; k represents the Boltzmann constant; T represents the thermodynamic temperature.

7. The molecular dynamics simulation method for quantifying the strength of intermolecular van der Waals forces according to claim 5, characterized in that: When polar molecules and non-polar molecules are close to each other, the charge distribution inside the polar molecules will induce the displacement of positive and negative charges inside the non-polar molecules, causing the centers of gravity of positive and negative charges inside the non-polar molecules to no longer coincide. The charges will be relatively displaced, thus generating an induced dipole effect. The interaction force generated between instantaneous dipoles is taken as the induced force. The calculation formula for the induced force is as follows: Where: E μiαj Represents the inductive force between polar molecules and non-polar molecules; μ i Represents the dipole moment of polar molecules; α j represents the polarizability between non-polar molecules; ε0 represents the vacuum permittivity; r represents the center of mass distance of the target molecule.

8. The molecular dynamics simulation method for quantifying the strength of intermolecular van der Waals forces according to claim 5, characterized in that: When non-polar molecules approach each other, instantaneous dipoles are generated, and the interaction force generated between the instantaneous dipoles is used as the dispersion force; the dispersion force calculation formula is as follows: Where: E αiαj Represents the dispersion force between two non-polar molecules; I i ,I j represents the ionization energy of two nonpolar molecules; α i , α j represents the polarizability of two non-polar molecules; ε0 represents the vacuum permittivity; r represents the center of mass distance of the target molecule.

9. The molecular dynamics simulation method for quantifying the strength of intermolecular van der Waals forces according to claim 4, characterized in that: The strength of the van der Waals force is calculated using the following formula: Where: E vdw Represents the strength of the van der Waals force between molecules; ε ij represents the LJ well depth between atoms i and j; r 0 ij represents the distance between atoms i and j at equilibrium; r ij Represents the distance between atoms i and j.

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