JPH1027187A - Method and device for analyzing adsorption or absorption process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To molecularly simulate a process or state for adsorbing/absorbing plural molecules to the inside/surface of a substance. SOLUTION: The method for molecularly simulating a process or a state for adsorbing/absorbing plural molecules to the inside/surface of a substance is provided with a CMC process for adsorbing/absorbing molecules to the inside/ surface of the subject by a canonical Monte Carlo method and an RC process for storing adsorbed/absorbed structure and defining the stored structure as initial structure to be used for the CMC process in succeeding repeated calculation. Then operation including the two processes is repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method and apparatus for analyzing, by molecular simulation, a process or a state in which molecules are adsorbed and / or absorbed on the inside and / or surface of a substance used in the field of chemical calculation.
In particular, it is used as a method for analyzing or predicting the physical properties of adsorbents and those having adsorbed physical properties handled in the chemical industry field. For example, it can be used as a means to simulate the process in which an adsorption substrate is adsorbed on an adsorbent, such as zeolite, which is used as a catalyst, or the process in which a hygroscopic polymer absorbs a hygroscopic component. . If the process of such adsorption and absorption can be easily calculated, it can be used for material design at the molecular level in the development of the material field, and the effect is great.

[0002]

2. Description of the Related Art BIOSYM / Molecular Simulati, USA
ons CERIUS2 and DISCOVER / INSI
With the rapid progress of numerical calculation speed of commercially available material design support software such as HGT and computers, the frequency of use for analysis and simulation at the molecular level is increasing. Molecular simulation is simulation of physical properties at the molecular level based on classical mechanics, quantum chemistry, statistical mechanics, and the like. For example, there are molecular simulation methods such as molecular dynamics calculation method, molecular force field calculation method, molecular orbital calculation method, Monte Carlo method, etc., molecular structure, dynamic behavior of molecules, electronic state of molecules, interaction between molecules. Etc. can be calculated.

[0003] Molecular simulation by the Monte Carlo method is described in, for example, "Introduction to Molecular Simulation" (Kaibudo,
As described in detail in page 63-80, 1989), when numerically analyzing the properties of individual particles as a group of liquids or solids or in them, the system is statistically mechanically analyzed. This is a method of simulation, and mathematically, a physical quantity between atoms is obtained by general numerical integration based on the Markov chain limit theorem. By using this principle, it is possible to analyze the state in which molecules are adsorbed and / or absorbed on the inside and / or surface of a substance. In short, the Monte Carlo method is a method that can simulate the state of a static substance.

[0004] For example, in commercially available software, US BIOSYM
/ There is a Resolution module of CERIUS2 which is material design support software of Molecular Simulations. In the CERIUS2 Resolution module, adsorption simulation using a canonical ensemble and a grand canonical ensemble is possible.

[0005] In the adsorption simulation using the canonical ensemble, the number of molecules to be analyzed and the internal and / or
Alternatively, it is possible to calculate the state of adsorption of a specific number of molecules on the inside and / or the surface of the substance when the volume of the surface structure and the temperature of the system are respectively constant. With this calculation method, the adsorption structure and the adsorption energy of the molecule inside and / or on the surface of the substance can be calculated.

In the adsorption simulation using the grand canonical ensemble, the adsorption state of a plurality of types of molecules inside and / or on the surface of a substance is determined by the chemical potential of each molecule, the volume of the internal and / or surface structure of the substance, and the temperature of the system. It can be determined under the conditions.

As can be seen from these examples, the Monte Carlo method is commonly used as a method for analyzing the state of a static substance. However, there is no known method of calculating a dynamic structural change such as a process in which a plurality of molecules are adsorbed and / or absorbed on the inside and / or surface of a substance and a state in the process by the Monte Carlo method.

On the other hand, as a method of calculating the state of a dynamic substance, a molecular dynamics calculation method is known. However, since this method depends on the initial structure when calculating, when calculating a dynamic structural change such as a process in which multiple molecules are adsorbed and / or absorbed on the inside and / or surface of a substance, Practical calculations are not possible, depending largely on the initial structure that generates the molecules to be adsorbed and / or absorbed.

Further, there is no known method for increasing the number of molecules one after another in a system to be simulated and analyzing the process.

Therefore, for example, a process in which water is gradually adsorbed on an adsorbent such as zeolite which is a porous material widely used in industry, and a process in which low molecules are gradually adsorbed in graphite. In addition, it has been difficult to analyze or predict the process in which the hygroscopic polymer absorbs water and changes its quality by molecular simulation.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for analyzing the process and state of a plurality of molecules adsorbing and / or absorbing on the inside and / or surface of a substance by using molecular simulation. It is in.

For example, the present invention relates to a process in which water is gradually adsorbed to an adsorbent such as zeolite which is widely used in industry, a process in which low molecules are gradually adsorbed in graphite, Provided is a method for calculating and analyzing processes in which a polymer absorbs water and changes in quality and states and the like in each process.

[0013]

Means for Solving the Problems The present inventors have conducted intensive studies on a method of analyzing the process or state of molecules adsorbing and / or absorbing on the inside and / or surface of a substance by molecular simulation, and as a result, the inside of the substance was found. As a method of analyzing the process or state in which a plurality of molecules are adsorbed and / or absorbed on a surface, and / or a method for analyzing (1) a step of adsorbing and / or absorbing molecules on a substance and / or a surface by a canonical Monte Carlo method (CM
C process).

(2) A step (R step) of defining the adsorbed and / or absorbed structure as an initial structure used in the CMC step of the next repetitive calculation.

An analysis method characterized by repeatedly performing an operation including the two steps has been found, and the present invention has been accomplished.

That is, the present invention provides a method for analyzing the process and the state of the adsorption and / or absorption of a plurality of molecules on the inside and / or the surface of a substance by molecular simulation. (1) A method of analyzing a substance and / or a substance by a canonical Monte Carlo method. Or the step of adsorbing and / or absorbing on the surface (CM
C process).

(2) A step (R step) of defining the adsorbed and / or absorbed structure as an initial structure used in the CMC step of the next repetitive calculation.

The present invention relates to an analysis method characterized by repeatedly performing an operation including the two steps.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below.

The inside and / or surface of the substance in the present invention may be any substance and its surface whose adsorption and / or state is to be evaluated. For example, porous materials such as zeolite and layered compound, silica, Examples thereof include inorganic substances such as alumina, and organic substances such as graphite, polyester-containing substances, and polystyrene-containing substances.

The molecule to be adsorbed and absorbed in the present invention may be any molecule as long as it can interact with the inside and / or the surface of the substance, and examples thereof include benzene, xylene, oxygen, nitrogen, and water. .

In the present invention, the process or state in which molecules are adsorbed and / or absorbed on the inside and / or the surface of a substance refers to the structure and energy of the molecules when they are successively adsorbed on the inside and / or the surface of the substance. Refers to a change process and / or state.

The canonical Monte Carlo method in the present invention is described in "Introduction to Molecular Simulation" (Kaibudo, pag
e69-71, 1989).
Refers to the Monte Carlo method by the VT ensemble. Examples of commercially available software include, for example, US BIOSYM / Mo
C, which is a material design support software of lecular Simulations
The Fixed loading simulation method incorporated in the ERIUS2 Resolution module can be used.

The calculation by the canonical Monte Carlo method in the present invention is, for example, as follows.

The structure of the target molecule to be adsorbed into the inside and / or the surface structure of the substance is generated by random numbers and inserted.
The molecules to be adsorbed are generated, for example, in a rigid state by changing the translation and rotation by random numbers. The arrangement of the generated molecules to be adsorbed is taken in with the following probability P by the Metropolis algorithm based on the change (ΔU) in the arrangement energy (adsorption interaction energy).

P = min (1; exp (−ΔU / kT)) k: Boltzmann constant T: temperature ΔU: change in configuration energy (adsorption interaction energy) Thereby, the most stable adsorption site and the most stable heat of adsorption are calculated. Can be calculated. The average heat of adsorption can be calculated by a statistical thermodynamic canonical ensemble average. When the arrangement is changed, the dihedral angle or angle between atoms in the molecule to be adsorbed, the bonding distance, or the like may be changed by a random number. The locations to be calculated using random numbers in order to change the arrangement include not only the rotation and translation of the structure of the molecule to be adsorbed, but also the dihedral angle, bond distance, bond angle, and / or the inside and / or inside of the molecule to be adsorbed.
Alternatively, it may be a dihedral angle, a bonding distance, or a bonding angle in the surface structure. These selections are appropriately selected depending on the target calculation system. For example, if the molecules to be adsorbed are benzene, nitrogen,
If the internal rotation of the molecule is apparent, such as carbon dioxide and water, the molecule to be adsorbed is treated as a rigid body, and only the rotation and translation of the molecular structure of the molecule to be adsorbed may be changed by random numbers. In the case of n-butane or glycerin having internal rotation in the molecule, the simulation can be performed in consideration of the internal rotation of the adsorbed molecule by changing the dihedral angle in the molecule to be adsorbed by a random number.

The process (CMC process) by the canonical Monte Carlo simulation in the present invention is calculated by the following method.

(1) As input data, the internal and / or surface structure of a substance and the structure of a target molecule to be adsorbed and / or absorbed are called.

These structural data are represented by xyz coordinates or
For crystal data, structural data coordinates based on a space group are preferable, but any structure data may be used as long as the structure is represented.

(2) A potential parameter is assigned to each atom of the called structure. The potential parameter is, for example, a DR that can be used in CERIUS2.
Although the EIDING parameter and the UNIVERSAL FORCE FIELD parameter are preferred, the present invention is not limited to any potential parameters.

(3) Assuming that the number of molecules to be simulated (N), the volume of the internal and / or surface structure of the substance (V), and the temperature of the system (T) are constant, respectively, the number of calculation steps, temperature, output The calculation is performed according to the method of the canonical Monte Carlo method. The calculation step needs to be changed depending on the object to be handled. In principle, it is necessary to calculate until the average thermodynamic interaction energy between the internal and / or surface structure of the substance and the target molecule to be adsorbed becomes constant, but it can be appropriately selected depending on the system to be calculated. The adsorption and / or absorption structure data output by the calculation is preferably in xyz coordinates, but may be any data as long as the structure can be expressed.

In the R step in the present invention, after the calculation of the CMC step is completed, an operation of storing structure data and the like and defining the adsorption structure data as an initial structure to be used in the next series of repetition steps is performed. At this time, the adsorption and / or absorption structure data calculated in the CMC process can be output or stored.

Substances and / or by adsorption and / or absorption
Alternatively, if the surface structure is considered to change, the step of optimizing the structure of the adsorption and / or structural data by molecular force field calculation and / or molecular dynamics calculation is periodically performed between the CMC step and the R step. It is preferred to add. The in-process structural optimization process is performed periodically to correct the structural distortion caused by the repeated CMC process.
It can be appropriately selected depending on the calculation time and the system to be handled. The molecular mechanics calculation method and the molecular force field calculation method used here are, for example, “Introduction to Molecular Simulation” (Kaibudo, page 37-62,
1989), the method described in detail in
A widely known material design support software such as US2 may be used.

FIG. 1 shows a flowchart of the adsorption simulation method according to the present invention, and FIG. 2 shows a conventional canonical Monte Carlo method. This method is hereinafter referred to as a continuous CMC method. The input data in FIG. 1 includes input data necessary for the CMC process, determination conditions, output conditions, and the like. The following are examples of the determination conditions.

(1) If the adsorption interaction energy calculated in each CMC step and / or the sum thereof is positive, the calculation is terminated.

(2) The number of repetitions N is set, and when it exceeds N, the calculation is terminated.

The judgment conditions are appropriately selected by the calculation system.
The molecule to be inserted can be changed for each CMC step. In each CMC process, suction structure data is output as output data and input data required in the next repetition process. When the calculation of the CMC process is completed according to the determination condition, output data of the entire calculation system is output.

The output data includes a calculation time, a graph of correspondence between the change in the adsorption energy of the entire system and the number of repetitions, a table, and the like. The result of the simulation can be observed with software capable of reading and visualizing the structural data, for example, CERIUS2.

By repeating the CMC step and the R step, and in some cases, the structure optimization step, the most stable adsorption and / or absorption structure can be sequentially obtained in each series of steps. Alternatively, it is possible to theoretically observe the process and state in which a plurality of molecules are adsorbed and / or absorbed on the surface. The adsorption or absorption structure obtained in the R step is continuously animated as 3
The three-dimensional display is very convenient because the process of adsorption and / or absorption can be visually observed.

[0040]

Next, the effects of the present invention will be described with reference to examples.

Example 1 Ba ion exchange type faujasite type zeolite BaX was selected as a material for adsorbing molecules inside a substance, and water was selected as a molecule for adsorbing, and calculations were performed by a continuous CMC method. The determination was performed by setting the number of repetitions to 300 times. The number of calculation steps in each CMC process was set to 200,000 steps.

(1) Potential Parameter and Structural Data The interatomic potential of guest-host (adsorbed molecule-zeolite) is based on the two-body central force potential given by the equations (1) to (3) (unit is kJ). / mol).

[0043]

(Equation 1) The interaction energy of guest-host in the system was obtained by calculating equation (4).

[0044]

(Equation 2) As the intermolecular force, a Lenard-Jones potential (6-12 type) was used. rij is the distance between i (zeolite) and j (water), D
The values of ij and Xij are the intermolecular force parameters derived from equations (2) and (3), Zi is the charge of the ion, and e is the elementary charge. The Lenard-Jones potential considered from the atom calculated by the cutoff to 8 angstroms. The electrostatic field potential was calculated using the ewald principle, and the cutoff value was set to 8 Å (default value).

BaX (silica / alumina ratio = 1.0 (m
ol / mol)) and the charge parameters on each atom are described in L. Uytterhoeven et al. (L. Uytterhoeven, D. Do
mpas, and WJ Morter, J. Chem. Farady Trans. 88
(1992) 2753). The structure of the added water is as follows: MOPAC (Ver.6.0) / MNDO method (JCPE # P016)
Was used. The Lenard-Jones potential parameter is described in documents such as AKRappe (AK
Rappe, CJ Casewit, KS Colwell, WA Goddar
d III and WM Skiff, J. Am. Chem. Soc. 114 (199
2) The Universal Force Feild parameter of 10024) was used. The electrostatic field potential parameter of water is BH
MNDO, ESP, and scaling methods described in Besler et al.
H. Besler, KM Merz, and A. Kollmann, J. Comput.
Chem. 11 (1990) 431).

(2) Continuous CMC calculation HP715 / 100 manufactured by HP was used as a computer. In the CMC process, under constant NVT conditions, at T = 273 K, the adsorption stable site and heat of adsorption of the adsorbate in one unit cell of faujasite-type zeolite were calculated by performing a simulation of 200,000 steps by the canonical Monte Carlo method. . The adsorbate water was generated using random numbers and inserted into the zeolite cell. The adsorbate is considered as one rigid body,
The arrangement was generated by changing the translation and rotation by random numbers. The arrangement of the generated adsorbates was taken in with the following probability P by the Metropolis algorithm based on the change (ΔU) in the arrangement energy (adsorption interaction energy).

P = min (1; exp (−ΔU / kT)) From this, the most stable adsorption site and the most stable heat of adsorption were calculated. The average heat of adsorption was calculated by a statistical thermodynamic canonical ensemble average.

The state of adsorption of a plurality of adsorbed water was obtained by continuously and continuously inserting water into BaX by the above-mentioned method by a continuous CMC method. 200,000 steps were calculated for each molecule, and 300 molecules were inserted. In each CMC process, energy minimization calculation between adsorbed water was performed by a molecular force field calculation method in order to suppress structural distortion due to repeated steps.

The CMC process was performed using CERIUS2's Sort
, and after the R process, the calculation of the structure optimization process is performed by the mechanics of CERIUS2. The control of a series of these repetitive calculations is created on HP-UX (ver. 9.0) which is the OS of the workstation. This was done using the SHELL script.

(3) Output Data The relationship between the calculation step of the 298th calculation in the CMC process and the adsorption interaction energy is shown in FIG.
Shown in According to FIG. 3, 200,000 steps are enough for 200,000 steps. FIG. 4 shows the relationship between the adsorption interaction energy and the number of inserted water molecules in each CMC step, and FIG. 5 shows the relationship between the total adsorption interaction energy between water molecules and BaX and the inserted water molecules. It can be seen that the adsorption energy of water molecules gradually decreases, and becomes energetically unstable at about 250 molecules. FIG. 6-9 shows the process and state of adsorption in which water molecules were sequentially inserted into BaX. Output was performed using visualizar of CERIUS2. Also, if the suction structure obtained in the R step is continuously and three-dimensionally displayed as an animation, it is very convenient because the suction process can be reproduced. It was found from the three-dimensional display of this calculation that water was adsorbed around the cation of zeolite. As described above, the continuous CMC method is a method of performing a molecular simulation of a process and a state in which molecules are adsorbed to the inside and / or the surface of a substance, and is very useful.

[0051]

As described above, a method for molecular simulation of a process and a state in which a plurality of molecules are adsorbed and / or absorbed on the inside and / or surface of a substance is as follows: (1) Adsorb molecules on the substance and / or surface by the canonical Monte Carlo method. And / or absorbing (CM)
C process).

(2) A step of storing the absorbed and / or absorbed structure and defining it as an initial structure used in the CMC step of the next repetitive calculation (R step).

The present inventors have found a simulation method characterized by repeatedly performing an operation including the two steps described above, and have become able to perform a molecular simulation of a process and a state in which a plurality of molecules are adsorbed and / or absorbed on the inside and / or the surface of a substance. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a flowchart of a continuous CMC method of the present invention.

FIG. 2 is a diagram showing a flowchart of a conventional CMC method.

FIG. 3 is a diagram showing the relationship between the calculation step of the 298th calculation in the CMC process and the adsorption interaction energy.

FIG. 4 is a diagram showing the relationship between the adsorption interaction energy of each CMC step and the number of inserted water molecules in a simulation of inserting water into BaX by the continuous CMC method.

FIG. 5 is a diagram showing the relationship between the total adsorption interaction energy between water molecules and BaX and the inserted water molecules in a simulation of inserting water into BaX by the continuous CMC method.

FIG. 6 is a diagram showing a part of the adsorption process and a state in which 50 molecules of water are inserted into BaX per unit cell by the continuous CMC method.

FIG. 7 is a diagram showing a part of the adsorption process and a state in which 200 molecules of water are inserted into BaX per unit cell by the continuous CMC method.

[Explanation of symbols]

 1: Ba ion 2: Zeolite skeleton 3: Water molecule

Claims (10)

[Claims] The present invention provides a method for analyzing a process or a state in which a plurality of molecules are adsorbed and / or absorbed on the inside and / or the surface of a substance by a molecular simulation. (1) A method for analyzing a molecule to a substance and / or a surface by a canonical Monte Carlo method. Adsorption and / or absorption process (CM
C process). (2) A step (R step) of defining the adsorbed and / or absorbed structure as an initial structure used in the CMC step of the next repetitive calculation. 2. A method for analyzing an adsorption or absorption process, comprising repeatedly performing an operation including the two steps of: 2. After a molecule is adsorbed and / or absorbed by a CMC process, a structure optimization process is performed by a molecular force field calculation method and / or a molecular dynamics calculation method, and a series of operations proceeding to the R process is periodically performed. The method for analyzing an adsorption or absorption process according to claim 1, wherein the method is applied. 3. The method of analyzing an adsorption or absorption process according to claim 1, wherein the calculation system is controlled by providing a judgment condition in the repeated calculation. 4. The method of analyzing an adsorption or absorption process according to claim 3, wherein the judgment condition is the number of repetitions. 5. The method of analyzing an adsorption or absorption process according to claim 3, wherein the judgment condition is set based on the interaction energy between the inside and / or the surface of the substance and the molecule to be adsorbed or absorbed. 6. The method for analyzing an adsorption or absorption process according to claim 1, wherein the substance to be adsorbed and / or absorbed is a porous material. 7. The method according to claim 6, wherein the porous material is zeolite. 8. The method for analyzing an adsorption or absorption process according to claim 1, wherein a process and a state of adsorbing water molecules on the inside and / or the surface of the zeolite are analyzed. 9. The method for analyzing an adsorption or absorption process according to claim 1, wherein a structure adsorbed and / or absorbed before the R step is output. 10. An analysis apparatus characterized by sequentially displaying the absorbed and / or absorbed structures obtained by the analysis method according to claim 9, and displaying the structures three-dimensionally as an animation.