Molecular dynamics modeling and analysis method for diffusion characteristics of water and ions in hydrated calcium silicate nanopores
Through molecular dynamics modeling and analysis methods, the diffusion characteristics of water and ions in hydrated calcium silicate nanopores are studied, and the problem of corrosion of concrete structures in marine environment or saline soil areas is solved due to corrosive ion penetration, providing a theoretical basis to improve the durability of cement-based materials.
Patent Information
- Application Number
- CN202510229843.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-28
- Publication Date
- 2025-06-27
AI Technical Summary
Concrete structures in marine environments or saline soil areas are corroded by corrosive ions penetration, affecting their durability, and the erosion process of water and ions is limited through relevant experiments.
A molecular dynamics modeling and analysis method for the diffusion characteristics of water and ions in hydrated calcium silicate nanopores is proposed, including establishing anhydrous calcium silicate model with broken silicon chains, adsorbing water molecules through the Monte Carlo method, constructing a solution model, and performing molecular dynamics simulation, using radial distribution function and mean square displacement analysis simulation results.
Through simulation, the interaction relationship between ions and the dynamic distribution data of ions are revealed, and the diffusion mechanism of water and ions in the hydrated calcium silicate pores is provided, which provides a theoretical basis for the design of the macro-mix ratio of cement-based materials and improves the service life of the material.
Smart Images
Figure CN120220836A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the technical field of molecular dynamics, and particularly to a molecular dynamics modeling and analysis method for the diffusion characteristics of water and ions in the nanopores of calcium silicate hydrate. Background Art
[0002] Cement-based materials (such as cement concrete) are the most widely used and important building materials in the world. Calcium silicate hydrate accounts for 50-70% of the cement hydration products and determines the durability of cement-based materials. Calcium silicate hydrate gel is a porous system with capillary pores and gel pores. The transport and adsorption behaviors of water and ions in its pores have a significant impact on the durability of cement-based materials.
[0003] During the process of conceiving and forming this application, the applicant has at least found the following problems. In concrete structures in marine environments or saline soil areas, erosive ions penetrate into the pores along with water molecules, corroding the concrete and the steel bars inside, affecting the durability of the concrete structure. However, there are many limitations in studying the erosion process of water and ions and the kinetic behaviors at the molecular level through relevant experiments. Summary of the Invention
[0004] In order to alleviate the above problems, the main purpose of this application is to propose a molecular dynamics modeling and analysis method for the diffusion characteristics of water and ions in the nanopores of calcium silicate hydrate, including the following steps:
[0005] S1. Establish a calcium silicate hydrate model without water and with silicon chain breakage;
[0006] S2. Use the Monte Carlo method to adsorb water molecules to the calcium silicate hydrate model in step S1 to obtain a water-absorbed calcium silicate hydrate model, and the size of the calcium silicate hydrate model is
[0007] S3. Expand the water-absorbed calcium silicate hydrate model in step S2 by 7 times on the Y-axis and 3 times on the Z-axis, and cut the middle part of the substrate from a preset plane to obtain a parallel substrate with a size of Tilt the substrate to construct a calcium silicate hydrate pore model with different pore inclinations;
[0008] S4. Construct a solution model through Packmol software;
[0009] S5. Combine the calcium silicate hydrate pore model in step S3 with the solution model in step S4 to form a solution ion diffusion model in the nanopores of calcium silicate hydrate;
[0010] S6. Perform molecular dynamics simulation on the solution ion diffusion model in the nanopores of calcium silicate hydrate in step S5;
[0011] S7. Analyze the simulation results obtained in step S6 using the radial distribution function (RDF) and the mean squared displacement (MSD). Obtain the interaction relationships between ions and water (Na-O), ions and ions (Na-Na, Na-Cl), and the C-S-H substrate and ions (Si-O, Ca-O) through RDF, and reveal the influence mechanism of the C-S-H substrate and water on ion diffusion. In addition, calculate the diffusion coefficients of water molecules and ions in different pores of C-S-H by MSD to evaluate the diffusion ability of water and ions in different pores. Combine the evaluation results of RDF and MSD to deeply analyze the diffusion characteristics of water and ions in the pores of C-S-H.
[0012] Optionally, step S1 is specifically: deleting the interlayer structural water of the tobermorite 11, which is a structural analog of calcium silicate hydrate, and deleting the bridged silicon-oxygen tetrahedrons in the silicon chain to obtain the anhydrous and silicon-chain-broken calcium silicate hydrate model. of the interlayer structural water, deleting the bridged silicon-oxygen tetrahedrons in the silicon chain to obtain the anhydrous and silicon-chain-broken calcium silicate hydrate model.
[0013] Optionally, the calcium-silicon ratio of the calcium silicate hydrate model obtained in step S1 is 1.67.
[0014] Optionally, the degree of polymerization distribution of the calcium silicate hydrate model obtained in step S1 is: Q0 = 10%, Q1 = 67%, Q2 = 23%.
[0015] Optionally, in step S2, the parameters used in the Monte Carlo method satisfy the following conditions: the force field function is ClayFF; the temperature is 300K; the time step is 0.01 fs; the electrostatic force uses Ewald summation; the van der Waals force uses Lennard-Jones; the results are output every 100,000 steps; the number of running steps is 200 ns;
[0016] Optionally, the substrate of the calcium silicate hydrate model obtained in step S3 is expanded 7 times along the Y-axis and 3 times along the Z-axis; or, expanded 7 times along the Z-axis and 3 times along the X-axis.
[0017] Optionally, the pore inclination angle of the calcium silicate hydrate pore model obtained in step S3 is 0° to 10°.
[0018] Optionally, the combination method of step S5 is divided into two types. One is that the large-aperture end of the substrate is used as the water inlet, and the corresponding small-aperture end is used as the water outlet; the other is that the large-aperture end of the substrate is used as the water outlet, and the corresponding small-aperture end is used as the water inlet.
[0019] Optionally, the upper end and / or the lower end of the calcium silicate hydrate substrate in the solution ion diffusion model in the calcium silicate hydrate nanopore obtained in step S5 is fixed to prevent the displacement of the calcium silicate hydrate substrate.
[0020] Optionally, in step S6, the parameters of the molecular dynamics simulation satisfy the following conditions: the ensemble is NVT; the temperature is 300 K; the force field is ClayFF; the electrostatic force uses Ewald summation; the van der Waals force uses Lennard-Jones; the time step is 1 fs; the results are output every 1000 steps; the simulation time is 3 ns.
[0021] Optionally, during the process of step S7, the peak of the RDF curve is calculated through the following expression to explain the interaction between ions:
[0022]
[0023] where dN is the number of molecules in the region with a distance from the center between (r, r + dr), ρ is the density of the system, and the radial distribution function g(r) can be interpreted as the ratio of the regional density of the system to the average density, which reflects the change of particle density with distance.
[0024] Optionally, during the analysis process of step S7, it also includes calculating the mean square displacement of atoms in the system through the following expression to reflect the motion state of atoms in the system:
[0025]
[0026] where MSD is the amount of mean square displacement, is the position vector of the atom at time t, is the position vector of the atom at the initial time.
[0027] The molecular dynamics modeling and analysis method for the diffusion characteristics of water and ions in the nano-pores of calcium silicate hydrate in this application constructs a calcium silicate hydrate model based on the molecular dynamics method, constructs a solution model through Packmol software, and then combines it into a solution ion diffusion model in the nano-pores of calcium silicate hydrate to perform molecular dynamics simulation. The radial distribution function and mean square displacement are used to analyze the simulation results. This application can evaluate the diffusion characteristics of water and ions in the nano-pores of calcium silicate hydrate through the interaction relationship between ions and the dynamic distribution data of ion movement obtained by simulation calculation, reveal the diffusion mechanism of ions in the pore structure of calcium silicate hydrate, provide the ion erosion process and penetration law in calcium silicate hydrate from the nano-scale, provide a theoretical basis for the macroscopic mix proportion design of cement-based materials such as concrete, and the analysis results can also guide and optimize the material design to further improve the service life of cement-based materials. Description of the Drawings
[0028] The accompanying drawings here are incorporated into the specification and form a part of this specification, showing embodiments consistent with this application, and are used together with the specification to explain the principles of this application. To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, other accompanying drawings can be obtained based on these drawings without creative efforts.
[0029] Figure 1 Schematic flow diagram of the molecular dynamics modeling and analysis method for water and ion diffusion characteristics in the calcium silicate hydrate nanopores of the specific implementation manner of this application.
[0030] Figure 2 Model diagram of water molecule diffusion in the calcium silicate hydrate nanopore in the first embodiment.
[0031] Figure 3 Model diagram of chloride ion diffusion in the calcium silicate hydrate nanopore in the second embodiment.
[0032] The realization, functional characteristics, and advantages of the purpose of this application will be further described in conjunction with the embodiments with reference to the accompanying drawings. Through the above accompanying drawings, the clear embodiments of this application have been shown, and there will be a more detailed description hereinafter. These accompanying drawings and textual descriptions are not intended to limit the scope of the concept of this application in any way, but to explain the concept of this application to those skilled in the art by referring to specific embodiments. Specific implementation manner
[0033] As Figure 1 shown, in the implementation manner of the present invention, the molecular dynamics modeling and analysis method for water and ion diffusion characteristics in the calcium silicate hydrate nanopore includes the following steps:
[0034] S1. Establish a calcium silicate hydrate model without water and with silicon chain breakage.
[0035] The establishment of the molecular dynamics model of this application mainly uses but is not limited to Material Studio software. Calcium silicate hydrate is a calcium silicate hydrated mineral with the chemical formula Ca5Si6O 16 (OH)·4H2O. Exemplarily, a calcium silicate hydrate model without water and with silicon chain defects (breakage) can be established by deleting the water in the layered analogue Tobermorite11 structure of the calcium silicate hydrate gel, and randomly deleting the silicon-oxygen tetrahedrons in the silicon chain according to the Qn distribution.
[0036] Optionally, step S1 is specifically: deleting the structural analogue Tobermorite11 of calcium silicate hydrate For the interlayer structured water, the bridged silicon oxygen tetrahedrons in the silicon chain are removed to obtain the anhydrous calcium silicate hydrate model with broken silicon chains.
[0037] Optionally, the calcium-silicon ratio of the calcium silicate hydrate model obtained in step S1 is 1.67.
[0038] Optionally, the degree of polymerization distribution of the calcium silicate hydrate model obtained in step S1 is: Q0 = 10%, Q1 = 67%, Q2 = 23%.
[0039] S2. Using the Monte Carlo method, water molecules are adsorbed onto the calcium silicate hydrate model in step S1 to obtain the calcium silicate hydrate model after water absorption. The size of the calcium silicate hydrate model is
[0040] The Grand Canonical Monte Carlo method (GCMC for short) is an important computational chemistry method, widely used in fields such as gas adsorption, ion adsorption, and solvent diffusion. The Monte Carlo method is a computational method that obtains statistical values by sampling surveys to estimate unknown characteristic quantities and is applicable to computational simulation experiments on discrete systems. The Grand Canonical Monte Carlo method is a computational chemistry method that combines the grand canonical ensemble and Monte Carlo simulation. In the Grand Canonical Monte Carlo method, the interactions between particles in the system and the interactions with the outside world are simulated through random sampling and probability distribution functions, and the system properties are obtained through statistical averages.
[0041] Exemplarily, in the computational simulation, by constructing a probability model similar to the system performance and conducting random experiments on a digital computer, the random characteristics of the water absorption system of the calcium silicate hydrate model can be simulated. Exemplarily, the calcium silicate hydrate model obtained in step S1 and the corresponding code in file can be submitted to LAMMPS for grand canonical Monte Carlo water absorption. Using the Monte Carlo method can make the error of the system independent of the dimension of the water absorption problem of the calcium silicate hydrate model. During the simulation process, there is no need to discretize continuous problems, and problems with statistical properties can be directly solved.
[0042] Optionally, in step S2, the parameters used in the Monte Carlo method satisfy the following conditions: the force field function is ClayFF; the temperature is 300K; the time step is 0.01 fs; the electrostatic force uses Ewald summation; the van der Waals force uses Lennard-Jones; the result is output every 100,000 steps; the simulation time is 200 ns.
[0043] S3. Expand the water-absorbed calcium silicate hydrate model in step S2 by 7 times along the Y-axis and 3 times along the Z-axis, and cut the middle part of the substrate from the preset plane to obtain a parallel substrate with dimensions of . Tilt the substrate to construct a calcium silicate hydrate pore model with different pore inclinations.
[0044] Exemplarily, using the LAMMPS large software toolkit, submit the water-absorbed calcium silicate hydrate model in step S2 and the corresponding script file to the program, and cut the middle part of the substrate from the plane (001). Exemplarily, use the del_atoms command to cut the expanded calcium silicate hydrate model into two parallel substrates from the middle part.
[0045] Optionally, the substrate of the calcium silicate hydrate model obtained in step S3 is expanded by 7 times along the Y-axis and 3 times along the Z-axis; or, it is expanded by 7 times along the Z-axis and 3 times along the X-axis.
[0046] Optionally, the pore inclination angle of the calcium silicate hydrate pore model obtained in step S3 is 0° to 10°.
[0047] S4. Construct a solution model through the Packmol software.
[0048] Exemplarily, Packmol is a software for constructing the initial model of molecular dynamics simulation. It can fill molecules within the spatial range according to the conditions set by the user to form different systems, such as spherical, tubular, and layered, etc. In this way, it can ensure that the short-range interaction repulsive force does not affect the simulation results.
[0049] S5. Combine the calcium silicate hydrate pore model in step S3 with the solution model in step S4 into a solution ion diffusion model in calcium silicate hydrate nanopores.
[0050] Exemplarily, using the LAMMPS large software toolkit, submit the calcium silicate hydrate pore model in step S3, the solution model in step S4, and the corresponding script file to the program for model combination.
[0051] Optionally, there are two ways of combination in step S5. One is that the large-pore diameter end of the substrate is used as the water inlet, and the corresponding small-pore diameter end is used as the water outlet; the other is that the large-pore diameter end of the substrate is used as the water outlet, and the corresponding small-pore diameter end is used as the water inlet.
[0052] Optionally, the upper end and / or the lower end of the calcium silicate substrate in the solution ion diffusion model in calcium silicate hydrate nanopores obtained in step S5 is fixed to prevent the displacement of the calcium silicate substrate.
[0053] S6. Perform molecular dynamics simulations on the solution ion diffusion model in the calcium silicate hydrate nanopores in step S5.
[0054] Exemplarily, use the LAMMPS large software toolkit to submit the relaxed model file output in step S5 and the corresponding script file to the program for molecular dynamics simulations. LAMMPS, whose full name is Large-scale Atomic / Molecular Massively Parallel Simulator, is a powerful software for simulating atomic and molecular systems, capable of providing corresponding codes for the calculation and analysis of the mean square displacement (MSD) and the radial distribution function (RDF). Among them, the radial distribution function (RDF) is a commonly used tool in molecular dynamics (MD) simulations to describe the spatial distribution of atoms or molecules at different distances. It can also be used to reveal the interactions and local structures of water molecules, ions, and C-S-H structural units. LAMMPS provides compute rdf to calculate the RDF. At the same time, the mean square displacement (MSD) is a commonly used analysis method in molecular dynamics (MD) simulations to study the average displacement of atoms or molecules over a certain period of time. The MSD can be used to calculate the self-diffusion coefficient and analyze the diffusion behavior of molecules in different environments, such as the diffusion characteristics of water molecules and ions in the pores of calcium silicate hydrate (C-S-H). LAMMPS provides the compute msd command to calculate the MSD and uses the fix ave / time command to view the calculation results. Optionally, in step S6, the parameters of the molecular dynamics simulation satisfy the following conditions: the ensemble is NVT; the temperature is 300 K; the force field is ClayFF; the electrostatic force uses Ewald summation; the van der Waals force uses Lennard-Jones; the time step is 1 fs; the results are output every 1000 steps; the simulation time is 3 ns.
[0055] S7. Analyze the simulation results obtained in step S6 using RDF and MSD. Obtain the interaction relationships between ions and water (Na-O), ions and ions (Na-Na, Na-Cl), and the C-S-H substrate and ions (Si-O, Ca-O) through RDF, and reveal the influence mechanism of the C-S-H substrate and water on ion diffusion. In addition, the MSD calculates the diffusion coefficients of water molecules and ions in different pores of C-S-H to evaluate the diffusion ability of water and ions in different pores. Combine the evaluation results of RDF and MSD to deeply analyze the diffusion characteristics of water and ions in C-S-H pores.
[0056] Exemplarily, according to the results of RDF and MSD obtained from the end of the simulation in step S6, the local structure of atoms at different positions can be reflected by the peak size and distribution width in the RDF graph; the kinetic dynamic characteristics of ions can be reflected by the MSD graph, which is used to analyze the differences in diffusion behaviors between ions.
[0057] Optionally, during the process of step S7, the peak of the RDF curve is calculated through the following expression to explain the interaction between ions:
[0058]
[0059] where dN is the number of molecules in the region with a distance from the center between (r, r + dr), ρ is the density of the system, and the radial distribution function g(r) can be interpreted as the ratio of the regional density to the average density of the system, which reflects the change of particle density with distance.
[0060] Optionally, during the analysis process of step S7, it also includes calculating the mean square displacement of atoms in the system through the following expression to reflect the motion state of atoms in the system:
[0061]
[0062] where MSD is the amount of mean square displacement; is the position vector of the atom at time t, is the position vector of the atom at the initial time.
[0063] The content of the present invention will be further described in detail through specific embodiments below. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.
[0064] Now, the implementation of each embodiment of the present application will be described with reference to the accompanying drawings. In the subsequent description, the suffixes such as "module", "component" or "unit" used to represent elements are only for the convenience of description of the present application, and they have no specific meaning themselves.
[0065] The main purpose of the present application is to propose a molecular dynamics modeling and analysis method for the diffusion characteristics of water and ions in the nano - pores of calcium silicate hydrate, Figure 1 which is a schematic flow diagram of the molecular dynamics modeling and analysis method for the diffusion characteristics of water and ions in the nano - pores of calcium silicate hydrate according to an embodiment of the present application.
[0066] The molecular dynamics modeling and analysis method for the diffusion characteristics of water molecules in the nano - pores of calcium silicate hydrate in the first embodiment specifically includes the following steps:
[0067] S1. Establish a model of calcium silicate hydrate (C - S - H) without water and with silicon chain defects (breaks).
[0068] The establishment of the molecular dynamics model of this application mainly uses, but is not limited to, Material Studio software;
[0069] Step S1 specifically includes the following steps: Delete the water in the layered analogue Tobermorite11 of calcium silicate hydrate gel, and randomly delete the silicon-oxygen tetrahedrons in the silicon chain according to the Qn distribution; where the polymerization degree Q distribution is: Q0 = 10%, Q1 = 67%, Q2 = 23%; the C / S ratio of the calcium silicate hydrate molecular model is 1.67; the box size after expanding the cell of the calcium silicate hydrate molecular dynamics model is Delete the water in the layered analogue Tobermorite11 of calcium silicate hydrate gel, and randomly delete the silicon-oxygen tetrahedrons in the silicon chain according to the Qn distribution; where the polymerization degree Q distribution is: Q0 = 10%, Q1 = 67%, Q2 = 23%; the C / S ratio of the calcium silicate hydrate molecular model is 1.67; the box size after expanding the cell of the calcium silicate hydrate molecular dynamics model is
[0070] S2. Use the Monte Carlo (GCMC) method to adsorb water molecules to the calcium silicate hydrate model in step S1 to obtain the calcium silicate hydrate model after water absorption.
[0071] Step S2 specifically includes the following steps: Submit the calcium silicate hydrate model obtained in step S1 and the corresponding code in file to LAMMPS for grand canonical Monte Carlo water absorption; where the force field function is set to ClayFF in the in file; the van der Waals force uses Lennard-Jones; the electrostatic force uses Ewald summation; the energy minimization method is the conjugate gradient algorithm; the temperature is 300K; the ensemble is NVT; the time step is 0.01fs; the atomic trajectory information is output every 100,000 steps; the simulation time is 200ns.
[0072] S3. Expand the calcium silicate hydrate model after water absorption in step S2 by 7 times on the Y axis and 3 times on the Z axis, and cut the middle part of the substrate from the plane (001) to obtain a parallel substrate with a size of and tilt the substrate to obtain the calcium silicate hydrate pore model with the corresponding angle.
[0073] Step S3 specifically includes the following steps:
[0074] Using the large software package LAMMPS, submit the hydrated calcium silicate model after water absorption in step S2 and the corresponding script file to the program. The specific parameters of the script file include the following: Read the model file through the read command; Define the atomic information in the model file; Set the force field function to ClayFF; Use the replicate command to expand the hydrated calcium silicate model in step S2; Cut the expanded hydrated calcium silicate model into two parallel substrates from the middle part using the del_atoms command; Tilt the parallel substrates at a corresponding angle using the fix command; Construct the hydrated calcium silicate pore model; Use Lennard-Jones for van der Waals forces; Use Ewald summation for electrostatic forces; The energy minimization method is the steepest descent algorithm; The temperature is 300 K; The ensemble is NVT; The time step is 1 fs; The simulation time is 500 ps.
[0075] S4. Construct a solution model using the Packmol software.
[0076] Step S4 specifically includes the following steps:
[0077] In the Packmol software, it should at least include the following conditions: A complete molecular structure file; A ClayFF force field information file; A complete input-output script file.
[0078] S5. Combine the hydrated calcium silicate pore model in step S3 and the solution model in step S4 into a water molecule diffusion model in the hydrated calcium silicate nanopore.
[0079] Step S5 specifically includes the following steps:
[0080] Using the large software package LAMMPS, submit the hydrated calcium silicate pore model in step S3, the solution model in step S4, and the corresponding script file to the program. The specific parameters of the script file include the following: Read the hydrated calcium silicate pore and solution model files using the read command; Define the atomic information in the model file; Set the force field function to ClayFF; Use Lennard-Jones for van der Waals forces; Use Ewald summation for electrostatic forces; The energy minimization method is the steepest descent algorithm; The temperature is 300 K; The ensemble is NVT; The time step is 1 fs; The simulation time is 500 ps.
[0081] S6. Perform molecular dynamics simulation on the water molecule diffusion model in the hydrated calcium silicate nanopore in step S5.
[0082] Step S6 specifically includes the following steps:
[0083] Using the large software toolkit LAMMPS, submit the relaxed model file output from step S5 and the corresponding script file to the program. The specific parameters of the script file include the following: Use the read command to read the model file of the combination of calcium silicate hydrate pores and solution; define the atomic information in the model file; set the force field function to ClayFF; use Lennard-Jones for van der Waals forces; use Ewald summation for electrostatic forces; use the conjugate gradient algorithm for energy minimization; the temperature is 300K; the ensemble is NVT; the time step is 1fs; the simulation time is 2ns.
[0084] S7. Analyze the simulation results obtained in step S6 using RDF and MSD. Through RDF, obtain the interaction relationships between ions and water (Na-O), ions and ions (Na-Na, Na-Cl), and between the C-S-H substrate and ions (Si-O, Ca-O), and reveal the influence mechanism of the C-S-H substrate and water on ion diffusion. In addition, calculate the diffusion coefficients of water molecules and ions in different pores of C-S-H using MSD to evaluate the diffusion ability of water and ions in different pores. Combine the evaluation results of RDF and MSD to deeply analyze the diffusion characteristics of water and ions in the pores of C-S-H.
[0085] Step S7 specifically includes the following steps:
[0086] According to the results of RDF and MSD obtained at the end of the simulation in step S6, the peak size and distribution width in the RDF graph can reflect the local structure of atoms at different positions; the MSD graph can reflect the dynamics of ions and is used to analyze the differences in diffusion behavior between ions.
[0087] Figure 2 It is a model diagram of the diffusion of water molecules in the calcium silicate hydrate nanopores in the first embodiment.
[0088] As Figure 2 shown, there are calcium atoms, silicon atoms, oxygen atoms, and hydrogen atoms in the model diagram of the diffusion of water molecules in the calcium silicate hydrate nanopores. Exemplarily, in the color model diagram, the brown ones are calcium atoms, the yellow ones are silicon atoms, the white ones are oxygen atoms, and the light blue ones are hydrogen atoms.
[0089] In this embodiment, through molecular dynamics simulation, select the force field function between atoms, set the simulation parameters and method steps, construct a model of the diffusion of water molecules in the calcium silicate hydrate nanopores, provide the diffusion mechanism of water molecules in the calcium silicate hydrate pores from the nanoscale, provide a theoretical basis for the macroscopic mix design of cement-based materials such as concrete, and the analysis results can also guide and optimize the material design to further improve the service life of cement-based materials.
[0090] Second Embodiment
[0091] In another embodiment, the molecular dynamics modeling and analysis method of chloride ion diffusion characteristics in calcium silicate hydrate nanopores specifically includes the following steps:
[0092] S1. Establish a CSH model without water and with silicon chain defects (breaks);
[0093] The specific steps include: mixing the layered analog of calcium silicate hydrate gel Tobermorite11 The water in the structure is deleted, and the silicon-oxygen tetrahedron in the silicon chain is randomly deleted according to the Qn distribution; the distribution of the degree of polymerization Q is: Q0 = 10%, Q1 = 67%, Q2 = 23%; the C / S ratio of the calcium silicate hydrate molecular model is 1.67; the box size of the calcium silicate hydrate molecular dynamics model after cell expansion is
[0094] S2, using the Monte Carlo (GCMC) method to adsorb water molecules to the calcium silicate hydrate model in step S1 to obtain a calcium silicate hydrate model after water absorption;
[0095] Specifically, the following steps are included: submitting the calcium silicate hydrate model obtained in step S1 and the corresponding code in file to LAMMPS for grand canonical Monte Carlo water absorption; wherein the force field function in the in file is set to ClayFF; the van der Waals force adopts Lennard-Jones; the electrostatic force adopts Ewald summation; the energy minimization method is the conjugate gradient algorithm; the temperature is 300K; the ensemble is NVT; the time step is 0.01fs; the atomic trajectory information is output once every 100,000 steps; and the simulation time is 100ns.
[0096] S3, the calcium silicate hydrate model that absorbs water in step S2 is expanded 7 times on the Y axis and 3 times on the Z axis, and the middle part of the substrate is cut from the plane (001) to obtain a size of The parallel base is tilted to construct calcium silicate hydrate pore models with different pore inclinations.
[0097] Specifically, it includes the following steps. Using the large software package LAMMPS, submit the hydrated calcium silicate model after water absorption in step S2 and the corresponding script file to the program. The specific parameters of the script file include the following: read the model file through the read command; define the atomic information in the model file; set the force field function as ClayFF; use the replicate command to expand the hydrated calcium silicate model in step S2; cut the expanded hydrated calcium silicate model into two parallel substrates from the middle part through the del_atoms command; use the fix command to perform the tilting operation at a corresponding angle on the parallel substrates; construct the hydrated calcium silicate pore model; use Lennard-Jones for the van der Waals force; use Ewald summation for the electrostatic force; the energy minimization method is the steepest descent algorithm; the temperature is 300K; the ensemble is NVT; the time step is 1fs; the simulation time is 500ps.
[0098] S4. Construct a sodium chloride solution model through the Packmol software.
[0099] Step S4 specifically includes the following steps:
[0100] In the Packmol software, it includes at least one of the following conditions: a complete molecular structure file; a ClayFF force field information file; a complete input-output script file.
[0101] S5. Combine the hydrated calcium silicate pore model in step S3 and the sodium chloride solution model in step S4 into a chloride ion diffusion model in the hydrated calcium silicate nanopore.
[0102] Specifically, it includes the following steps. Using the large software package LAMMPS, submit the hydrated calcium silicate pore model in step S3, the sodium chloride solution model in step S4, and the corresponding script file to the program. The specific parameters of the script file include the following: use the read command to read the hydrated calcium silicate pore and solution model files; define the atomic information in the model file; set the force field function as ClayFF; use Lennard-Jones for the van der Waals force; use Ewald summation for the electrostatic force; the energy minimization method is the steepest descent algorithm; the temperature is 300K; the ensemble is NVT; the time step is 1fs; the simulation time is 500ps.
[0103] S6. Perform molecular dynamics simulation on the chloride ion diffusion model in the hydrated calcium silicate nanopore in step S5.
[0104] Specifically, it includes the following steps. Using the large software toolkit LAMMPS, submit the relaxed model file output in step S5 and the corresponding script file to the program. The specific parameters of the script file include the following: Use the read command to read the model file after the combination of the pores of calcium silicate hydrate and sodium chloride solution; Define the atomic information in the model file; Set the force field function to ClayFF; Use Lennard-Jones for van der Waals forces; Use Ewald summation for electrostatic forces; The energy minimization method is the conjugate gradient algorithm; The temperature is 300K; The ensemble is NVT; The time step is 1fs; The simulation time is 2ns.
[0105] S7. Use RDF and MSD to analyze the simulation results obtained in step S6. Through RDF, obtain the interaction relationships between ions and water (Na-O), ions and ions (Na-Na, Na-Cl), and between the C-S-H substrate and ions (Si-O, Ca-O), and reveal the influence mechanism of the C-S-H substrate and water on ion diffusion. In addition, MSD calculates the diffusion coefficients of water molecules and ions in different pores of C-S-H to evaluate the diffusion ability of water and ions in different pores. Combining the evaluation results of RDF and MSD, deeply analyze the diffusion characteristics of water and ions in the pores of C-S-H.
[0106] Figure 3 It is a model diagram of chloride ion diffusion in the calcium silicate hydrate nanopores of the second embodiment.
[0107] As Figure 3 shown, in the model diagram of chloride ion diffusion in the calcium silicate hydrate nanopores, there are calcium atoms, silicon atoms, oxygen atoms, hydrogen atoms, sodium ions, and chloride ions. Exemplarily, in the color model diagram, the brown ones are calcium atoms, the yellow ones are silicon atoms, the white ones are oxygen atoms, the light blue ones are hydrogen atoms, the purple ones are sodium ions, and the pink ones are chloride ions.
[0108] In this embodiment, based on molecular dynamics simulation, a diffusion model of chloride ions in calcium silicate hydrate nanopores is constructed. Starting from the atomic perspective, it reveals the physical and chemical reactions of chloride ions in the pore structure of calcium silicate hydrate, expounds the erosion principle of chloride ions on cement-based materials, provides theoretical support for reducing the durability of cement-based materials by chloride ions from the nanoscale perspective, and provides a basis for designing concrete structures with higher durability.
[0109] This application constructs a calcium silicate hydrate model based on molecular dynamics simulation, constructs a solution model through Packmol software, and combines them into an ion diffusion model in the nanopores of calcium silicate hydrate for molecular dynamics simulation. The radial distribution function and mean square displacement are used to analyze the simulation results. This application can evaluate the diffusion characteristics of water and ions in the nanopores of calcium silicate hydrate through the obtained interaction relationships between ions and the dynamic distribution data of ion movement, reveal the reaction mechanism of ions in the pore structure of calcium silicate hydrate, provide the ion erosion process and penetration law in calcium silicate hydrate from the nanoscale, provide a theoretical basis for the macroscopic mix design of cement-based materials such as concrete, and the analysis results can also guide and optimize material design to further improve the service life of cement-based materials.
[0110] It should be noted that in this application, step codes such as S1 and S2 are used. The purpose is to more clearly and briefly express the corresponding content and do not constitute a substantial limitation in order. Those skilled in the art may execute S2 first and then S1 during specific implementation, etc., but these should all be within the protection scope of this application.
[0111] It can be understood that the above scenarios are only examples and do not constitute a limitation on the application scenarios of the technical solutions provided by the embodiments of this application. The technical solutions of this application can also be applied to other scenarios. For example, as is known to those of ordinary skill in the art, with the evolution of the device architecture and the emergence of new service scenarios, the technical solutions provided by the embodiments of this application are equally applicable to similar technical problems.
[0112] The serial numbers of the above embodiments of this application are only for description and do not represent the superiority or inferiority of the embodiments.
[0113] The steps in the method of the embodiments of this application can be adjusted, combined, and deleted according to actual needs.
[0114] The units in the devices of the embodiments of this application can be combined, divided, and deleted according to actual needs.
[0115] In this application, for the description of the same or similar term concepts, technical solutions, and / or application scenarios, generally only a detailed description is made when it first appears. When it appears repeatedly later, for the sake of brevity, it is generally not repeated. When understanding the technical solutions and other contents of this application, for the same or similar term concepts, technical solutions, and / or application scenarios that are not detailed later, reference can be made to their relevant detailed descriptions before.
[0116] In this application, the descriptions of each embodiment have their own emphases. For the parts not detailed or recorded in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.
[0117] The technical features of the technical solution of this application can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope recorded in this application.
[0118] The above are only the preferred embodiments of this application, and do not limit the scope of this application. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of this application, or directly or indirectly applied to other related technical fields, shall be included in the scope of protection of this application by the same token.
Claims
1. A molecular dynamics modeling and analysis method for water and ion diffusion characteristics in calcium silicate hydrate nanopores, characterized in that: The steps include: S1. Establish a model of calcium silicate hydrate without water and with broken silicon chains; S2. Using the Monte Carlo method, the calcium silicate hydrate model in step S1 is subjected to water molecule adsorption to obtain a calcium silicate hydrate model after water absorption. The size of the calcium silicate hydrate model is S3, the calcium silicate hydrate model that absorbs water in step S2 is expanded 7 times on the Y axis and 3 times on the Z axis, and the middle part of the substrate is cut from the preset plane to obtain a size of The parallel base is tilted, and the calcium silicate hydrate pore models with different inclinations are constructed according to the actual macroscopic pore structure of calcium silicate hydrate; S4, constructing a solution model using Packmol software; S5, combining the calcium silicate hydrate pore model of step S3 and the solution model of step S4 into a solution ion diffusion model in calcium silicate hydrate nanopores; S6, performing molecular dynamics simulation on the solution ion diffusion model in the calcium silicate hydrate nanopores of step S5; S7. The simulation results obtained in step S6 were analyzed using radial distribution function (RDF) and mean square displacement (MSD). The interaction relationship between ions and water (Na-O), ions and ions (Na-Na, Na-Cl), and CSH substrate and ions (Si-O, Ca-O) was obtained through RDF, revealing the influence mechanism of CSH substrate and water on ion diffusion. In addition, the diffusion coefficients of water molecules and ions in different pores of CSH were calculated by MSD to evaluate the diffusion capacity of water and ions in different pores. Combining the evaluation results of RDF and MSD, the diffusion characteristics of water and ions in CSH pores are deeply analyzed.
2. The molecular dynamics modeling and analysis method for water and ion diffusion characteristics in calcium silicate hydrate nanopores according to claim 1, characterized in that: Step S1 specifically includes: deleting the structural analogues of calcium silicate hydrate The interlayer structure of water deletes the silicon-oxygen tetrahedron bridging the silicon chain to obtain the anhydrous calcium silicate hydrate model with broken silicon chains.
3. The molecular dynamics modeling and analysis method for water and ion diffusion characteristics in calcium silicate hydrate nanopores according to claim 1, characterized in that: The calcium-silicon ratio of the calcium silicate hydrate model obtained in step S1 is 1.67; And / or, the polymerization degree distribution of the calcium silicate hydrate model obtained in step S1 is: Q0=10%, Q1=67%, Q2=23%.
4. The molecular dynamics modeling and analysis method for water and ion diffusion characteristics in calcium silicate hydrate nanopores according to claim 1, characterized in that: In step S2, the parameters used in the Monte Carlo method meet the following conditions: the force field function is ClayFF; the temperature is 300K; the time step is 0.01fs; the electrostatic force adopts Ewald summation; the van der Waals force adopts Lennard-Jones; the result is output once every 100,000 steps; and the number of running steps is 200ns.
5. The molecular dynamics modeling and analysis method for water and ion diffusion characteristics in calcium silicate hydrate nanopores according to claim 1, characterized in that: The base of the calcium silicate hydrate model obtained in step S3 is expanded 7 times in the Y axis and 3 times in the Z axis; or, is expanded 7 times in the Z axis and 3 times in the X axis; And / or, the pore inclination angle of the calcium silicate hydrate pore model obtained in step S3 is 0° to 10°.
6. The molecular dynamics modeling and analysis method for water and ion diffusion characteristics in calcium silicate hydrate nanopores according to claim 1, characterized in that: There are two combinations of step S5: one end of the substrate with a large aperture is used as the water inlet, and the corresponding end with a small aperture is used as the water outlet; or one end of the substrate with a large aperture is used as the water outlet, and the corresponding end with a small aperture is used as the water inlet; And / or, the upper and / or lower end of the calcium silicate hydrate substrate in the solution ion diffusion model in the calcium silicate hydrate nanopore obtained in step S5 Fixation is performed to prevent displacement of the calcium silicate hydrate substrate.
7. The molecular dynamics modeling and analysis method for water and ion diffusion characteristics in calcium silicate hydrate nanopores according to claim 1, characterized in that: In step S6, the parameters of the molecular dynamics simulation meet the following conditions: the ensemble is NVT; the temperature is 300K; the force field is ClayFF; the electrostatic force adopts Ewald summation; the van der Waals force adopts Lennard-Jones; the time step is 1 fs; the result is output once every 1000 steps; and the simulation time is 3 ns.
8. The molecular dynamics modeling and analysis method for water and ion diffusion characteristics in calcium silicate hydrate nanopores according to claim 1, characterized in that: During the analysis process of step S7, the peaks of the RDF curve are calculated by the following expression to explain the interaction between ions; Where dN is the number of molecules in the region with a distance from the center (r, r+dr), ρ is the density of the system, and the radial distribution function g(r) can be interpreted as the ratio of the regional density to the average density of the system, which reflects the change of particle density with distance.
9. The molecular dynamics modeling and analysis method for water and ion diffusion characteristics in calcium silicate hydrate nanopores according to any one of claims 1 to 8, characterized in that: The analysis process of step S7 also includes calculating the mean square displacement of atoms in the system by the following expression to reflect the motion state of atoms in the system: Where MSD is the mean square displacement, is the position vector of the atom at time t, is the position vector of the atom at the initial moment.