Molecular dynamics simulation method and system for calculating interfacial tension between fluids

Abstract

The invention belongs to the technical field of oil-gas exploration and development, and discloses a molecular dynamics simulation method and system for calculating interfacial tension between fluids, and the method comprises the steps: constructing a fluid interface model through molecular dynamics simulation software, and carrying out balance molecular dynamics simulation; a normal pressure tensor component and a tangential pressure tensor component at an interface are calculated based on the local number density of fluid molecules in an interface area and corresponding parameters such as simulation temperature and model volume, and the interfacial tension is further solved through the difference value of the pressure tensor components. According to the invention, the interfacial tension value between different fluid media can be rapidly and accurately measured, and theoretical guidance is provided for researching the interfacial behavior of the fluid and the interfacial action mechanism between different fluids.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas exploration and development, and specifically relates to a molecular dynamics simulation method and system for calculating interfacial tension between fluids. Background Art

[0002] Interfacial tension is a key parameter for studying the interaction between crude oil and other fluids in the field of oil and gas exploration and development technology, especially when it comes to crude oil-water, crude oil-CO2 and other systems. For the immiscible crude oil-water system, interfacial tension is the dominant factor affecting the emulsification, separation and other processes; and in the crude oil-CO2 system, interfacial tension is one of the important indicators to measure the effectiveness of CO2 oil recovery. The interfacial tension between CO2 and crude oil will change with the dynamic changes of temperature and pressure. When the interfacial tension between oil and gas approaches 0, the interface between CO2 and crude oil tends to be blurred. At this time, CO2 can achieve miscible drive, which can efficiently displace crude oil from the pores of complex reservoirs, greatly improving the recovery rate of crude oil. Therefore, in-depth research on the interfacial tension between fluids is of great significance for improving crude oil recovery.

[0003] The molecular dynamics simulation method can not only realize extreme conditions that are difficult to achieve under experimental conditions, such as high temperature, high pressure, vacuum, etc., but also reveal the distribution, arrangement and interaction of fluid molecules at the interface from a microscopic perspective, and has significant advantages in quantifying the interfacial tension between fluids. Therefore, it provides a theoretical basis for rationally formulating oil reservoir exploration and development plans and improving crude oil recovery. The present invention provides a molecular dynamics simulation method for calculating the interfacial tension between fluids. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a molecular dynamics simulation method and system for calculating the interfacial tension between fluids, which can quickly and accurately measure the interfacial tension values ​​between different fluid media, provide theoretical guidance for studying the interfacial behavior of fluids and the interfacial action mechanism between different fluids, and lay the foundation for the efficient development of oil reservoirs.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A molecular dynamics simulation method for calculating interfacial tension between fluids, the method comprising:

[0007] S1. Construct a fluid interface model based on molecular dynamics simulation software and carry out equilibrium molecular dynamics simulation;

[0008] S2, calculating the normal pressure tensor component and the tangential pressure tensor component at the interface by balancing the molecular dynamics simulation parameters;

[0009] S3. Obtain the interfacial tension through the pressure tensor components.

[0010] Preferably, in S1, constructing a fluid interface model based on molecular dynamics simulation software includes:

[0011] S11. Determine the chemical formula, molecular structure and standard density of the two fluid components under simulated temperature and pressure conditions;

[0012] S12, determining the three-dimensional size of the model system and the number of molecules required for the two fluid models;

[0013] S13, combining the two fluid models to form a model structure of fluid 1-fluid 2-fluid 1 through molecular dynamics simulation software;

[0014] The specific calculation formula is:

[0015]

[0016] Where V is the volume of the model; x, y, and z are the dimensions of the model along the x, y, and z directions, respectively; m is the atomic mass in the model; ρ is the density; N is the number of molecules required in the model; N A Avogadro's constant is 6.02×10 23 ; M is the molar mass of the molecular chain.

[0017] Preferably, in S1, carrying out equilibrium molecular dynamics simulation comprises:

[0018] S14, selecting force field parameters to describe the interaction between fluid molecules;

[0019] S15, performing energy minimization processing on the model;

[0020] S16. Set the temperature and pressure conditions of the model, and select an ensemble that meets the preset requirements to carry out equilibrium molecular dynamics simulation;

[0021] The specific calculation formula is:

[0022] The calculation area is equally divided along the model direction, and the statistical formula for the molecular number density in a single area is:

[0023]

[0024] Where: ρ(y) represents the molecular density in the region; n(y) represents the number of molecules in the region; V s Represents the volume of the region;

[0025] The regional volume calculation formula is:

[0026]

[0027] Where: V sRepresents the volume of the region; L x represents the length of the region along the x-axis; △y represents the length of the region divided along the y-axis; L z Represents the length of the region along the z-axis;

[0028] The model temperature is the preset simulation temperature value during the equilibrium molecular dynamics simulation.

[0029] Preferably, in S2, calculating the normal pressure tensor component and the tangential pressure tensor component at the interface by balancing the molecular dynamics simulation parameters comprises:

[0030] The formula for the normal pressure tensor components is:

[0031]

[0032] Where: P N (y) represents the normal pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; y ij represents the distance between atoms i and j along the y-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r;

[0033] The formula for the tangential pressure tensor components is:

[0034]

[0035] Where: P T (y) represents the tangential pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; x ij represents the distance between atoms i and j along the x-axis; z ij represents the distance between atoms i and j along the z-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r.

[0036] Preferably, in S3, obtaining the interfacial tension through the pressure tensor component comprises:

[0037]

[0038] Where: γ represents the interfacial tension; L y Represents the length of the model along the y-axis; P N (y) represents the normal pressure tensor component; PT (y) represents the tangential pressure tensor component.

[0039] The present invention also provides a molecular dynamics simulation system for calculating interfacial tension between fluids, the system being used to implement any one of the methods described, the system comprising: a model building module, a tensor calculation module and a tension calculation module;

[0040] The model building module is used to build a fluid interface model based on molecular dynamics simulation software and carry out equilibrium molecular dynamics simulation;

[0041] The tensor calculation module is used to calculate the normal pressure tensor component and the tangential pressure tensor component at the interface by balancing the molecular dynamics simulation parameters;

[0042] The tension calculation module is used to obtain the interfacial tension through the pressure tensor component.

[0043] Preferably, the model building module includes: a first determining unit, a second determining unit and a combining unit;

[0044] The first determination unit is used to determine the chemical formula and molecular structure of the two fluid components and the standard density of the fluids under simulated temperature and pressure conditions;

[0045] The second determination unit is used to determine the three-dimensional size of the constructed model system and the number of molecules required for the two fluid models;

[0046] The combining unit is used to combine the two fluid models to form a model structure of fluid 1-fluid 2-fluid 1 through molecular dynamics simulation software;

[0047] The specific calculation formula is:

[0048]

[0049]

[0050]

[0051] Where V is the volume of the model; x, y, and z are the dimensions of the model along the x, y, and z directions, respectively; m is the atomic mass in the model; ρ is the density; N is the number of molecules required in the model; N A Avogadro's constant is 6.02×10 23 ; M is the molar mass of the molecular chain.

[0052] Preferably, the model building module further includes: a selection unit, a processing unit and a simulation unit;

[0053] The selection unit is used to select force field parameters to describe the interaction between fluid molecules;

[0054] The processing unit is used to perform energy minimization processing on the model;

[0055] The simulation unit is used to set the temperature and pressure conditions of the model and select an ensemble that meets the preset requirements to carry out equilibrium molecular dynamics simulation;

[0056] The specific calculation formula is:

[0057] The calculation area is equally divided along the model direction, and the statistical formula for the molecular number density in a single area is:

[0058]

[0059] Where: ρ(y) represents the molecular density in the region; n(y) represents the number of molecules in the region; V s Represents the volume of the region;

[0060] The regional volume calculation formula is:

[0061]

[0062] Where: V s Represents the volume of the region; L x represents the length of the region along the x-axis; △y represents the length of the region divided along the y-axis; L z Represents the length of the region along the z-axis;

[0063] The model temperature is the preset simulation temperature value during the equilibrium molecular dynamics simulation.

[0064] Preferably, in the tensor calculation module, calculating the normal pressure tensor component and the tangential pressure tensor component at the interface by balancing the molecular dynamics simulation parameters includes:

[0065] The formula for the normal pressure tensor components is:

[0066]

[0067] Where: P N (y) represents the normal pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; y ij represents the distance between atoms i and j along the y-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r;

[0068] The formula for the tangential pressure tensor components is:

[0069]

[0070] Where: P T (y) represents the tangential pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; x ij represents the distance between atoms i and j along the x-axis; z ij represents the distance between atoms i and j along the z-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r.

[0071] Preferably, in the tension calculation module, obtaining the interfacial tension through the pressure tensor component includes:

[0072]

[0073] Where: γ represents the interfacial tension; L y Represents the length of the model along the y-axis; P N (y) represents the normal pressure tensor component; P T (y) represents the tangential pressure tensor component.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] The present invention provides a molecular dynamics simulation method and ablation for calculating the interfacial tension between fluids. The molecular dynamics simulation method is used to construct a fluid interface model and carry out a balanced molecular dynamics simulation process. The normal pressure tensor component and the tangential pressure tensor component at the interface are calculated based on the local number density of molecules in the fluid interface region and the corresponding simulation temperature, model volume and other parameters, and the interfacial tension is further calculated by the difference of the pressure tensor components. The present invention can quickly and accurately measure the interfacial tension value between different fluid media, provide theoretical guidance for studying the interfacial behavior of fluids and the interfacial action mechanism between different fluids, and lay the foundation for the efficient development of oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0077] Figure 1 This is a flow chart of a molecular dynamics simulation method for calculating interfacial tension between fluids in an embodiment of the present invention;

[0078] Figure 2 In the embodiment of the present invention, the component is C 12 H 26 The single chain structure model diagram of crude oil;

[0079] Figure 3 A diagram showing a single-chain structure model of a water molecule in an embodiment of the present invention;

[0080] Figure 4 In the embodiment of the present invention, the component is C 10 H 22 Crude oil structure model diagram;

[0081] Figure 5 A single-chain structural model diagram of a CO2 molecule in an embodiment of the present invention;

[0082] Figure 6 This is a structural diagram of the oil-water fluid interface model in an embodiment of the present invention;

[0083] Figure 7 Schematic diagram of the oil-gas fluid interface model in an embodiment of the present invention. DETAILED DESCRIPTION

[0084] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0085] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0086] Embodiment 1

[0087] like Figure 1 As shown, this embodiment provides a molecular dynamics simulation method for calculating the interfacial tension between fluids, including the following steps: constructing a fluid interface model based on molecular dynamics simulation software and conducting equilibrium molecular dynamics simulation, calculating the normal pressure tensor component and the tangential pressure tensor component at the interface based on the local number density of fluid molecules in the interface area and the corresponding model temperature and volume parameters, and further obtaining the interfacial tension between fluids through the pressure tensor components, laying a foundation for the efficient development of oil reservoirs.

[0088] To achieve the above objectives, the specific implementation process is as follows:

[0089] In this embodiment, a fluid interface system model is constructed by molecular dynamics simulation software: first, the chemical formula, molecular structure and standard density of the two fluid components under simulated temperature and pressure conditions are determined; second, the three-dimensional size of the constructed model system is determined; finally, the number of molecules required to construct the model system is calculated by a formula, and the calculation formula is as follows:

[0090] (1)

[0091] (2)

[0092] (3)

[0093] Where V is the volume of the model; x, y, and z are the dimensions of the model along the x, y, and z directions, respectively; m is the atomic mass in the model; ρ is the density; N is the number of molecules required in the model; N A Avogadro's constant is 6.02×10 23 ; M is the molar mass of the molecular chain.

[0094] In this embodiment, performing equilibrium molecular dynamics simulation includes:

[0095] Select force field parameters to describe the interaction between fluid molecules and perform energy minimization on the model;

[0096] Set the temperature and pressure conditions of the model, select the NVT ensemble (canonical ensemble) to ensure that the number of molecules, model volume and temperature inside the system remain constant, and carry out equilibrium molecular dynamics simulation;

[0097] In this embodiment, the normal pressure tensor component and the tangential pressure tensor component at the interface are calculated by balancing the molecular dynamics simulation results, wherein the pressure tensor component is solved based on parameters such as the local number density of fluid molecules in the model interface region, the model temperature and volume;

[0098] Specifically, the calculation area is evenly divided along the model direction, and the local number density of fluid molecules in a single area is counted. The calculation formula is as follows:

[0099] (4)

[0100] Where: ρ(y) represents the molecular density in the region; n(y) represents the number of molecules in the region; V s Represents the volume of the region.

[0101] Specifically, the volume of a single region after the model is evenly divided is calculated using the following formula:

[0102] (5)

[0103] Where: V s Represents the volume of the region; L x represents the length of the region along the x-axis; △y represents the length of the region divided along the y-axis; L z Indicates the length of the region along the z-axis.

[0104] Specifically, the model temperature is the simulation temperature value preset during the equilibrium molecular dynamics simulation;

[0105] Specifically, the normal pressure tensor component value at the interface is calculated by using the parameters such as the fluid molecular density, model temperature and volume in the above interface region. The calculation formula is as follows:

[0106] (6)

[0107] Where: P N (y) represents the normal pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; y ij represents the distance between atoms i and j along the y-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r;

[0108] Calculate the tangential pressure tensor component at the interface again, and the calculation formula is as follows:

[0109] (7)

[0110] Where: P T (y) represents the tangential pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; x ij represents the distance between atoms i and j along the x-axis; z ij represents the distance between atoms i and j along the z-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r;

[0111] In this embodiment, the interfacial tension is further calculated based on the above-mentioned normal pressure tensor component and tangential pressure tensor component values, and the interfacial tension calculation formula is as follows:

[0112] (8)

[0113] Where: γ represents the interfacial tension; L yRepresents the length of the model along the y-axis; P N (y) represents the normal pressure tensor component; P T (y) represents the tangential pressure tensor component.

[0114] Embodiment 2

[0115] The present invention provides a molecular dynamics simulation method for calculating the interfacial tension between fluids, specifically measuring the interfacial tension value of the oil-water interface.

[0116] S1. In this embodiment, crude oil C 12 H 26 Based on the water molecule H2O, the C 12 H 26 and the molecular single chain structure model of H2O; Figure 2 , Figure 3 As shown;

[0117] S2, the simulation temperature is set to 353K, the simulation pressure is 20MPa environment, and by querying NIST, it can be known that C 12 H 26 The density of H2O molecules is 0.723 g / cm 3 and 0.981 g / cm 3 ;

[0118] S2. Establish the required target model with a total size of 2.45 nm×3.3 nm×7.6 nm; and further calculate the required number of oil molecules and water molecules by the formula:

[0119] (1)

[0120] (2)

[0121] (3)

[0122] Where V is the volume of the model; x, y, and z are the dimensions of the model along the x, y, and z directions, respectively; m is the atomic mass in the model; ρ is the density; N is the number of molecules required in the model; N A Avogadro's constant is 6.02×10 23 ; M is the molar mass of the molecular chain.

[0123] S3. Conduct equilibrium molecular dynamics simulation, select appropriate force field parameters to describe the interaction between fluid molecules, and perform energy minimization on the model;

[0124] S4, set the model temperature to 353K, the simulation pressure to 20MPa, and select a suitable ensemble to carry out equilibrium molecular dynamics simulation;

[0125] S5, calculating the normal pressure tensor component and the tangential pressure tensor component at the interface by balancing the molecular dynamics simulation results (the local number density of fluid molecules in the model interface region) and related parameters (model temperature and model volume);

[0126] S6. Divide the model into regions along the y direction, divide the regions equally, and count the local number density of fluid molecules in a single region. The calculation formula is as follows:

[0127] (4)

[0128] Where: ρ(y) represents the molecular density in the region; n(y) represents the number of molecules in the region; V s Represents the volume of the region.

[0129] S7. Calculate the volume of a single region after the model is evenly divided. The calculation formula is as follows:

[0130] (5)

[0131] Where: V s Represents the volume of the region; L x represents the length of the region along the x-axis; △y represents the length of the region divided along the y-axis; L z Indicates the length of the region along the z-axis.

[0132] S8, model temperature is the simulation temperature value preset during the equilibrium molecular dynamics simulation;

[0133] S9. Calculate the normal pressure tensor component value at the interface by using the parameters such as the fluid molecular density, model temperature and volume in the above interface region. The calculation formula is as follows:

[0134] (6)

[0135] Where: P N (y) represents the normal pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; y ij represents the distance between atoms i and j along the y-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r;

[0136] S10. Calculate the tangential pressure tensor component value at the interface again. The calculation formula is as follows:

[0137] (7)

[0138] Where: P T (y) represents the tangential pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; x ij represents the distance between atoms i and j along the x-axis; z ij represents the distance between atoms i and j along the z-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r;

[0139] S11. Further calculate the interfacial tension based on the above normal pressure tensor component and tangential pressure tensor component values. The interfacial tension calculation formula is as follows:

[0140] (8)

[0141] Where: γ represents the interfacial tension; L y Represents the length of the model along the y-axis; P N (y) represents the normal pressure tensor component; P T (y) represents the tangential pressure tensor component.

[0142] S12, obtain a stable oil-water interface structure by molecular dynamics simulation method, such as Figure 6 As shown, the normal pressure tensor component and the tangential pressure tensor component at the interface of the fluid model in the equilibrium stage are output, and the interfacial tension value at the fluid interface is further obtained to be 47.58 mN / m.

[0143] Embodiment 3

[0144] The present invention provides a molecular dynamics simulation method for calculating the interfacial tension between fluids, specifically for measuring the interfacial tension value of the oil-gas interface.

[0145] S1. In this embodiment, crude oil C 10 H 22 Based on the CO2 molecule, the C 10 H 22 and the molecular single chain structure model of CO2; Figure 4 , Figure 5 As shown;

[0146] S2, the simulation temperature is set to 353K, the simulation pressure is 6MPa environment, and by querying NIST, it can be known that C 10 H 22 The density of CO2 molecules is 0.710 g / cm3 and 0.097 g / cm 3 ;

[0147] S2. Establish the required target model with a total size of 2.8 nm×3.6 nm×8.5 nm; and further calculate the required number of oil molecules and CO2 molecules by the formula:

[0148] (1)

[0149] (2)

[0150] (3)

[0151] Where V is the volume of the model; x, y, and z are the dimensions of the model along the x, y, and z directions, respectively; m is the atomic mass in the model; ρ is the density; N is the number of molecules required in the model; N A Avogadro's constant is 6.02×10 23 ; M is the molar mass of the molecular chain.

[0152] S3. Conduct equilibrium molecular dynamics simulation, select appropriate force field parameters to describe the interaction between fluid molecules, and perform energy minimization on the model;

[0153] S4. Set the model temperature to 353K, the simulation pressure to 6MPa, and select a suitable ensemble to carry out equilibrium molecular dynamics simulation;

[0154] S5, calculating the normal pressure tensor component and the tangential pressure tensor component at the interface by balancing the molecular dynamics simulation results (the local number density of fluid molecules in the model interface region) and related parameters (model temperature and model volume);

[0155] S6. Divide the model into regions along the y direction, divide the regions equally, and count the local number density of fluid molecules in a single region. The calculation formula is as follows:

[0156] (4)

[0157] Where: ρ(y) represents the molecular density in the region; n(y) represents the number of molecules in the region; V s Represents the volume of the region.

[0158] S7. Calculate the volume of a single region after the model is evenly divided. The calculation formula is as follows:

[0159] (5)

[0160] Where: V s Represents the volume of the region; L xrepresents the length of the region along the x-axis; △y represents the length of the region divided along the y-axis; L z Indicates the length of the region along the z-axis.

[0161] S8, model temperature is the simulation temperature value preset during the equilibrium molecular dynamics simulation;

[0162] S9. Calculate the normal pressure tensor component value at the interface by using the parameters such as the fluid molecular density, model temperature and volume in the above interface region. The calculation formula is as follows:

[0163] (6)

[0164] Where: P N (y) represents the normal pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; y ij represents the distance between atoms i and j along the y-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r;

[0165] S10. Calculate the tangential pressure tensor component value at the interface again. The calculation formula is as follows:

[0166] (7)

[0167] Where: P T (y) represents the tangential pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; x ij represents the distance between atoms i and j along the x-axis; z ij represents the distance between atoms i and j along the z-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r;

[0168] S11. Further calculate the interfacial tension based on the above normal pressure tensor component and tangential pressure tensor component values. The interfacial tension calculation formula is as follows:

[0169] (8)

[0170] Where: γ represents the interfacial tension; L y Represents the length of the model along the y-axis; P N (y) represents the normal pressure tensor component; PT (y) represents the tangential pressure tensor component.

[0171] S12, obtain a stable oil-gas interface structure through molecular dynamics simulation method, such as Figure 7 As shown, the normal pressure tensor component and the tangential pressure tensor component at the interface of the fluid model in the equilibrium stage are output, and the interfacial tension value at the fluid interface is further obtained to be 10.47 mN / m.

[0172] Embodiment 4

[0173] The present invention also provides a molecular dynamics simulation system for calculating interfacial tension between fluids, the system being used to implement any one of the methods described, the system comprising: a model building module, a tensor calculation module and a tension calculation module;

[0174] Model building module, used to build fluid interface models based on molecular dynamics simulation software and conduct equilibrium molecular dynamics simulations;

[0175] A tensor calculation module, used for calculating the normal pressure tensor component and the tangential pressure tensor component at the interface by balancing the molecular dynamics simulation parameters;

[0176] The tension calculation module is used to obtain the interfacial tension through the pressure tensor components.

[0177] In this embodiment, the model building module includes: a first determining unit, a second determining unit and a combining unit;

[0178] A first determination unit is used to determine the chemical formula and molecular structure of the two fluid components and the standard density of the fluids under simulated temperature and pressure conditions;

[0179] The second determination unit is used to determine the three-dimensional size of the constructed model system and the number of molecules required for the two fluid models;

[0180] A combination unit, used for combining two fluid models to form a model structure of fluid 1-fluid 2-fluid 1 through molecular dynamics simulation software;

[0181] The specific calculation formula is:

[0182]

[0183]

[0184]

[0185] Where V is the volume of the model; x, y, and z are the dimensions of the model along the x, y, and z directions, respectively; m is the atomic mass in the model; ρ is the density; N is the number of molecules required in the model; N AAvogadro's constant is 6.02×10 23 ; M is the molar mass of the molecular chain.

[0186] In this embodiment, the model building module further includes: a selection unit, a processing unit and a simulation unit;

[0187] Select units to select force field parameters to describe the interaction between fluid molecules;

[0188] A processing unit, used for performing energy minimization processing on the model;

[0189] The simulation unit is used to set the temperature and pressure conditions of the model and select an ensemble that meets the preset requirements to carry out equilibrium molecular dynamics simulation;

[0190] The specific calculation formula is:

[0191] The calculation area is equally divided along the model direction, and the statistical formula for the molecular number density in a single area is:

[0192]

[0193] Where: ρ(y) represents the molecular density in the region; n(y) represents the number of molecules in the region; V s Represents the volume of the region;

[0194] The regional volume calculation formula is:

[0195]

[0196] Where: V s Represents the volume of the region; L x represents the length of the region along the x-axis; △y represents the length of the region divided along the y-axis; L z Represents the length of the region along the z-axis;

[0197] The model temperature is the preset simulation temperature value during the equilibrium molecular dynamics simulation.

[0198] In this embodiment, in the tensor calculation module, the normal pressure tensor component and the tangential pressure tensor component at the interface are calculated by balancing the molecular dynamics simulation parameters, including:

[0199] The formula for the normal pressure tensor components is:

[0200]

[0201] Where: P N (y) represents the normal pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23; T(y) represents temperature; V(y) represents area volume; y ij represents the distance between atoms i and j along the y-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r;

[0202] The formula for the tangential pressure tensor components is:

[0203]

[0204] Where: P T (y) represents the tangential pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; x ij represents the distance between atoms i and j along the x-axis; z ij represents the distance between atoms i and j along the z-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r.

[0205] In this embodiment, in the tension calculation module, obtaining the interfacial tension through the pressure tensor component includes:

[0206]

[0207] Where: γ represents the interfacial tension; L y Represents the length of the model along the y-axis; P N (y) represents the normal pressure tensor component; P T (y) represents the tangential pressure tensor component.

[0208] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A molecular dynamics simulation method for calculating interfacial tension between fluids, characterized in that: The method comprises: S1. Construct a fluid interface model based on molecular dynamics simulation software and carry out equilibrium molecular dynamics simulation; S2, calculating the normal pressure tensor component and the tangential pressure tensor component at the interface by balancing the molecular dynamics simulation parameters; S3, obtaining the interfacial tension through the pressure tensor components; In S1, constructing a fluid interface model based on molecular dynamics simulation software includes: S11. Determine the chemical formula, molecular structure and standard density of the two fluid components under simulated temperature and pressure conditions; S12, determining the three-dimensional size of the model system and the number of molecules required for the two fluid models; S13, combining the two fluid models to form a model structure of fluid 1-fluid 2-fluid 1 through molecular dynamics simulation software; The specific calculation formula is: Where V is the volume of the model; x, y, and z are the dimensions of the model along the x, y, and z directions, respectively; m is the atomic mass in the model; ρ is the density; N is the number of molecules required in the model; N A Avogadro's constant is 6.02×10 23 ; M is the molar mass of the molecular chain.

2. The method according to claim 1, characterized in that In S1, carrying out equilibrium molecular dynamics simulation includes: S14, selecting force field parameters to describe the interaction between fluid molecules; S15, performing energy minimization processing on the model; S16. Set the temperature and pressure conditions of the model, and select an ensemble that meets the preset requirements to carry out equilibrium molecular dynamics simulation; The specific calculation formula is: The calculation area is equally divided along the model direction, and the statistical formula for the molecular number density in a single area is: Where: ρ(y) represents the molecular density in the region; n(y) represents the number of molecules in the region; V s Represents the volume of the region; The regional volume calculation formula is: Where: V s Represents the volume of the region; L x represents the length of the region along the x-axis; △y represents the length of the region divided along the y-axis; L z Represents the length of the region along the z-axis; The model temperature is the preset simulation temperature value during the equilibrium molecular dynamics simulation.

3. The method according to claim 1, characterized in that In S2, calculating the normal pressure tensor component and the tangential pressure tensor component at the interface by balancing the molecular dynamics simulation parameters includes: The formula for the normal pressure tensor components is: Where: P N (y) represents the normal pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; y ij represents the distance between atoms i and j along the y-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r; The formula for the tangential pressure tensor components is: Where: P T (y) represents the tangential pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; x ij represents the distance between atoms i and j along the x-axis; z ij represents the distance between atoms i and j along the z-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r.

4. The method according to claim 1, characterized in that In S3, obtaining the interfacial tension through the pressure tensor component includes: Where: γ represents the interfacial tension; L y Represents the length of the model along the y-axis; P N (y) represents the normal pressure tensor component; P T (y) represents the tangential pressure tensor component.

5. A molecular dynamics simulation system for calculating interfacial tension between fluids, the system being used to implement the method according to any one of claims 1 to 4, characterized in that: The system comprises: a model building module, a tensor calculation module and a tension calculation module; The model building module is used to build a fluid interface model based on molecular dynamics simulation software and carry out equilibrium molecular dynamics simulation; The tensor calculation module is used to calculate the normal pressure tensor component and the tangential pressure tensor component at the interface by balancing the molecular dynamics simulation parameters; The tension calculation module is used to obtain the interfacial tension through the pressure tensor component.

6. The system according to claim 5, characterized in that The model building module includes: a first determining unit, a second determining unit and a combining unit; The first determination unit is used to determine the chemical formula and molecular structure of the two fluid components and the standard density of the fluids under simulated temperature and pressure conditions; The second determination unit is used to determine the three-dimensional size of the constructed model system and the number of molecules required for the two fluid models; The combining unit is used to combine the two fluid models to form a model structure of fluid 1-fluid 2-fluid 1 through molecular dynamics simulation software; The specific calculation formula is: Where V is the volume of the model; x, y, and z are the dimensions of the model along the x, y, and z directions, respectively; m is the atomic mass in the model; ρ is the density; N is the number of molecules required in the model; N A Avogadro's constant is 6.02×10 23 ; M is the molar mass of the molecular chain.

7. The system according to claim 5, characterized in that The model building module also includes: a selection unit, a processing unit and a simulation unit; The selection unit is used to select force field parameters to describe the interaction between fluid molecules; The processing unit is used to perform energy minimization processing on the model; The simulation unit is used to set the temperature and pressure conditions of the model and select an ensemble that meets the preset requirements to carry out equilibrium molecular dynamics simulation; The specific calculation formula is: The calculation area is equally divided along the model direction, and the statistical formula for the molecular number density in a single area is: Where: ρ(y) represents the molecular density in the region; n(y) represents the number of molecules in the region; V s Represents the volume of the region; The regional volume calculation formula is: Where: V s Represents the volume of the region; L x represents the length of the region along the x-axis; △y represents the length of the region divided along the y-axis; L z Represents the length of the region along the z-axis; The model temperature is the preset simulation temperature value during the equilibrium molecular dynamics simulation.

8. The system according to claim 5, characterized in that In the tensor calculation module, the normal pressure tensor component and the tangential pressure tensor component at the interface are calculated by balancing the molecular dynamics simulation parameters, including: The formula for the normal pressure tensor components is: Where: P N (y) represents the normal pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; y ij represents the distance between atoms i and j along the y-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r; The formula for the tangential pressure tensor components is: Where: P T (y) represents the tangential pressure tensor component; ρ(y) represents the molecular number density in the region; k B represents the Boltzmann constant, 1.38×10 -23 ; T(y) represents temperature; V(y) represents area volume; x ij represents the distance between atoms i and j along the x-axis; z ij represents the distance between atoms i and j along the z-axis; r ij represents the distance between atoms i and j; dφ(r) / dr is the derivative of the potential function with respect to r.

9. The system according to claim 5, characterized in that In the tension calculation module, obtaining the interfacial tension through the pressure tensor component includes: Where: γ represents the interfacial tension; L y Indicates the length of the model along the y-axis; P N (y) represents the normal pressure tensor component; P T (y) represents the tangential pressure tensor component.

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