Information processing device, information processing method, and program

Abstract

This information processing device comprises: a molecular dynamics calculation means for calculating the motion of a molecular group including atoms and / or molecules using molecular dynamics calculation; an average square displacement calculation means for calculating an average square displacement for each atom and molecule; a diffusion coefficient calculation means for calculating a diffusion coefficient for each atom and molecule on the basis of the average square displacement for each atom and molecule; a fitting means for fitting the cumulative probability of the diffusion coefficient with a cumulative distribution function; and a diffusion coefficient determination means for determining a diffusion coefficient for the molecular group on the basis of the fitted cumulative distribution function.

Description

Information processing device, information processing method, and program

[0001] The present disclosure relates to an information processing device, an information processing method, and a program.

[0002] For example, one conventionally known method for calculating the diffusion coefficient is to use molecular dynamics calculations to calculate the motion of atoms and molecules, determine the mean square displacement of each atom and molecule over time, average the mean square displacement of each atom and molecule over time, and calculate the gradient of the averaged mean square displacement with respect to time as the diffusion coefficient.

[0003] Patent Document 1 discloses a technique for determining a diffusion coefficient using molecular dynamics calculations.

[0004] Patent No. 3309820

[0005] In molecular dynamics calculations, due to the characteristics of the method, the distance traveled by each atom and molecule varies. As a result, the number and extent of large movement of atoms and molecules tends to vary from trial to trial. In conventional methods for calculating the diffusion coefficient, atoms and molecules that move more significantly contribute more to the diffusion coefficient, and these large movements can lead to overestimation or variations in the diffusion coefficient.

[0006] On the other hand, in the conventional method for calculating the diffusion coefficient, it is not preferable to arbitrarily ignore atoms and molecules that have moved significantly, because atoms and molecules that have moved significantly are also elements that express the diffusion phenomenon.

[0007] An object of the present disclosure is to provide an information processing device, an information processing method, and a program that improve the accuracy of the diffusion coefficient of a molecular group calculated using molecular dynamics calculations.

[0008] The present disclosure has the following configuration.

[0009] [1] An information processing device comprising: molecular dynamics calculation means for calculating the motion of a molecular group including at least one of atoms and molecules using molecular dynamics calculation; mean square displacement calculation means for calculating a mean square displacement for each of the atoms and molecules; diffusion coefficient calculation means for calculating a diffusion coefficient for each of the atoms and molecules based on the mean square displacement for each of the atoms and molecules; fitting means for fitting a cumulative probability of the diffusion coefficient with a cumulative distribution function; and diffusion coefficient determination means for determining a diffusion coefficient of the molecular group based on the fitted cumulative distribution function.

[0010] [2] The information processing device according to [1], wherein the diffusion coefficient determining means determines a representative value of the diffusion coefficient of the molecule group using the fitted cumulative distribution function.

[0011] [3] The information processing device according to [1] or [2], wherein the cumulative distribution function is an error function or a complementary error function.

[0012] [4] The information processing device according to any one of [1] to [3], wherein the diffusion coefficient of the molecular group is a diffusion coefficient of a polymer group that diffuses on a surface.

[0013] [5] The information processing device according to any one of [1] to [4], wherein the molecule group is a lubricant molecule group that constitutes a lubricant layer of a magnetic recording medium.

[0014] [6] An information processing method, in which an information processing device performs: a molecular dynamics calculation procedure for calculating the motion of a molecular group including at least one of atoms and molecules using molecular dynamics calculation; a mean square displacement calculation procedure for calculating a mean square displacement for each of the atoms and molecules; a diffusion coefficient calculation procedure for calculating a diffusion coefficient for each of the atoms and molecules based on the mean square displacement for each of the atoms and molecules; a fitting procedure for fitting a cumulative probability of the diffusion coefficient with a cumulative distribution function; and a diffusion coefficient determination procedure for determining a diffusion coefficient of the molecular group based on the fitted cumulative distribution function.

[0015] [7] A program for causing an information processing device to execute the following steps: a molecular dynamics calculation step of calculating the motion of a molecular group including at least one of atoms and molecules using molecular dynamics calculation; a mean square displacement calculation step of calculating a mean square displacement for each of the atoms and molecules; a diffusion coefficient calculation step of calculating a diffusion coefficient for each of the atoms and molecules based on the mean square displacement for each of the atoms and molecules; a fitting step of fitting a cumulative probability of the diffusion coefficient with a cumulative distribution function; and a diffusion coefficient determination step of determining a diffusion coefficient of the molecular group based on the fitted cumulative distribution function.

[0016] According to the present disclosure, it is possible to provide an information processing device, an information processing method, and a program that improve the accuracy of the diffusion coefficient of a molecular group calculated using molecular dynamics calculations.

[0017] FIG. 1 is a configuration diagram of an example of an information processing system according to the present embodiment; FIG. 2 is a hardware configuration diagram of an example of a computer according to the present embodiment; FIG. 3 is a graph showing the mean square displacement for each molecule, using lubricant molecules as an example; FIG. 4 is an explanatory diagram of an example of a self-diffusion coefficient calculated by a general method; FIG. 5 is an explanatory diagram of an example of a self-diffusion coefficient calculated by a general method; FIG. 6 is an explanatory diagram of an example of a method according to the present embodiment for calculating a diffusion coefficient; FIG. 7 is an explanatory diagram of an example of a method according to the present embodiment for calculating a diffusion coefficient; FIG. 8 is a functional configuration diagram of an example of an information processing system according to the present embodiment; FIG. 9 is a flowchart showing an example of a processing procedure of the information processing system according to the present embodiment.

[0018] Next, an embodiment of the present invention will be described in detail, but the present invention is not limited to the following embodiment.

[0019] [First embodiment] <System configuration> Fig. 1 is a configuration diagram of an example of an information processing system 1 according to this embodiment. The information processing system 1 in Fig. 1 includes a server device 10 and a client terminal 12. The server device 10 and the client terminal 12 of the information processing system 1 are connected to each other so as to be able to communicate data with each other via a communication network 18 such as a local area network (LAN) or the Internet.

[0020] The client terminal 12 is an information processing device operated by a worker, such as a PC, tablet terminal, or smartphone. The client terminal 12 displays a screen on a display device for accepting information input from the worker and accepts the information input from the worker. The client terminal 12 also sends a processing request to the server device 10 in accordance with the worker's input, causing the server device 10 to execute the processing. The client terminal 12 receives information on the execution results of the processing from the server device 10, displays it on a display device, and allows the worker to confirm it.

[0021] The server device 10 is an information processing device such as a PC or a workstation. The server device 10 receives a processing request from the client terminal 12 and executes the processing. The server device 10 transmits processing result information to the client terminal 12 and causes the client terminal 12 to display the processing result information.

[0022] The information processing system 1 may be realized by a server device 10 that provides a program download function to a client terminal 12, and the client terminal 12 that executes the downloaded program. The client terminal 12 that executes the program calculates the diffusion coefficient of a molecular group using molecular dynamics calculations as described below, and displays the result on a display device, for example, for confirmation by an operator.

[0023] Molecular dynamics calculations are a method for tracking the movement of atoms and molecules according to the laws of physics, and can calculate physical quantities related to the movement of atoms and molecules, such as the diffusion coefficient. Some physical quantities, such as the diffusion coefficient, can fluctuate significantly in value due to rare events.

[0024] The information processing system 1 may be realized by a server device 10 having a web server function and a client terminal 12 that executes a web application using a web browser function. The client terminal 12 that executes the web application using the web browser function displays the diffusion coefficient of a molecular group calculated by the server device 10 having the web server function using molecular dynamics calculation as described below on, for example, a display device, for confirmation by an operator.

[0025] The information processing system 1 may be realized by cooperative processing between the client terminal 12 that executes a program and the server device 10. The client terminal 12 that executes the program and the server device 10 perform cooperative processing to calculate the diffusion coefficient of a molecular group using molecular dynamics calculations as described below, and display the calculated diffusion coefficient of the molecular group on, for example, a display device for confirmation by an operator.

[0026] 1 is merely an example, and it goes without saying that there are various system configurations depending on the application and purpose. For example, the server device 10 may be realized by multiple computers that perform processing in cooperation with each other, or may be realized as a cloud computing service. The information processing system 1 may also be realized by a standalone computer.

[0027] <Hardware Configuration> The server device 10 and the client terminal 12 in FIG. 1 are realized by, for example, a computer 500 having the hardware configuration shown in FIG.

[0028] Fig. 2 is a hardware configuration diagram of an example of a computer 500 according to this embodiment. The computer 500 in Fig. 2 includes an input device 501, a display device 502, an external I / F 503, a RAM (Random Access Memory) 504, a ROM (Read Only Memory) 505, a CPU (Central Processing Unit) 506, a communication I / F 507, and an HDD (Hard Disk Drive) 508, all of which are interconnected by a bus B. The input device 501 and the display device 502 may be connected to each other for use.

[0029] The input device 501 is a touch panel, operation keys, buttons, keyboard, mouse, etc. that an operator uses to input various signals. The display device 502 is composed of a display such as a liquid crystal or organic EL display for displaying a screen, and a speaker for outputting audio data such as voice or sound. The communication I / F 507 is an interface through which the computer 500 performs data communication.

[0030] The HDD 508 is an example of a non-volatile storage device that stores programs and data. The stored programs and data include an OS, which is basic software that controls the entire computer 500, and application programs that provide various functions on the OS. The computer 500 may use a drive device (such as a solid-state drive (SSD)) that uses flash memory as a storage medium instead of or in addition to the HDD 508.

[0031] The external I / F 503 is an interface with an external device. The external device may be a recording medium 503a. This allows the computer 500 to read and / or write data from and to the recording medium 503a via the external I / F 503. The recording medium 503a may be a flexible disk, a CD, a DVD, an SD memory card, a USB memory, or the like.

[0032] The ROM 505 is an example of a non-volatile semiconductor memory (storage device) that can retain programs and data even when the power is turned off. The ROM 505 stores programs and data such as the BIOS, OS settings, and network settings that are executed when the computer 500 starts up. The RAM 504 is an example of a volatile semiconductor memory (storage device) that temporarily retains programs and data.

[0033] The CPU 506 is a computing device that reads programs and data from storage devices such as the ROM 505 and HDD 508 onto the RAM 504 and executes processing to realize overall control and functions of the computer 500. The computer 500 according to this embodiment can realize various functions of the server device 10 and the client terminal 12 by executing programs.

[0034] The program to be installed in the RAM 504 is installed, for example, by reading the program recorded on the recording medium 503a via the external I / F 503. Alternatively, the program may be installed by being downloaded from the communication network 18 via the communication I / F 507.

[0035] <Method for Determining Diffusion Coefficient> Here, to facilitate understanding of the method for determining a diffusion coefficient according to this embodiment, the method will be described in comparison with a general method for determining a diffusion coefficient. Hereinafter, atoms and molecules may be simply referred to as molecules.

[0036] One common method for calculating the diffusion coefficient is to use molecular dynamics to calculate the motion of a group of molecules and calculate the mean square displacement (u ２ ) is calculated, and the calculated mean square displacement is averaged between molecules to calculate the diffusion coefficient using, for example, the following equation (1). Equation (1) shows an example of an equation for calculating the self-diffusion coefficient. In equation (1), the slope of the averaged mean square displacement with respect to time is calculated as the self-diffusion coefficient.

[0037] In molecular dynamics calculations, due to the characteristics of the method, the mean square displacement of each molecule is likely to differ, as shown in FIG. 3, for example. FIG. 3 is a graph showing the mean square displacement of each molecule using lubricant molecules as an example. The lubricant molecules are, for example, a compound represented by the following chemical formula (1). Note that an average line showing the average of the mean square displacements of each molecule is added to the graph in FIG. 3. As shown in FIG. 3, the mean square displacement of each molecule included in a molecular group differs from molecule to molecule. For example, in FIG. 3, the mean square displacement of about one-third of the molecules is significantly higher than the average line.

[0038]

[0039] 4A and 4B are explanatory diagrams of an example of a self-diffusion coefficient obtained by a general method. The self-diffusion coefficient for each molecule obtained by the general method varies as shown in FIG. 4A. The distribution of the self-diffusion coefficient for each molecule in FIG. 4A obtained by the general method is shown in FIG. 4B, for example.

[0040] 4B shows the distribution of the self-diffusion coefficient of a molecule obtained by a general method and the average line showing the self-diffusion coefficient of a molecular group. As shown in Fig. 4B, the self-diffusion coefficient of a molecular group obtained by a general method is largely contributed by molecules (rare molecules) whose self-diffusion coefficients are significantly higher than the average shown in region 1000 of Fig. 4A, and the molecules that move significantly cause the diffusion coefficient of the molecular group to be overestimated or to vary.

[0041] Therefore, in the method according to the present embodiment for calculating the diffusion coefficient, the motion of a group of molecules is calculated using molecular dynamics calculations, the mean square displacement of each molecule over time is calculated, and the self-diffusion coefficient of each molecule is calculated using equation (1) based on the calculated mean square displacement of each molecule. Furthermore, in the method according to the present embodiment for calculating the diffusion coefficient, the calculated self-diffusion coefficient of each molecule is plotted, for example, as shown in FIG. 5A. FIG. 5 is an explanatory diagram of an example of the method according to the present embodiment for calculating the diffusion coefficient. In FIG. 5A, the vertical axis represents the cumulative probability, and the horizontal axis represents the self-diffusion coefficient.

[0042] Furthermore, in the method according to the present embodiment for determining the diffusion coefficient, the curve of the self-diffusion coefficient for each molecule obtained as shown in FIG. 5A is regressed by a cumulative distribution function, and the self-diffusion coefficient of the molecular group is calculated based on the regressed cumulative distribution function.

[0043] 5B shows the distribution of the self-diffusion coefficient of a molecule calculated by the method according to the present embodiment for calculating the diffusion coefficient, and the average line showing the self-diffusion coefficient of a group of molecules. Fig. 5B is a Gaussian distribution obtained by differentiating the cumulative distribution function of Fig. 5A.

[0044] As shown in Fig. 5B, the method for calculating the diffusion coefficient according to this embodiment provides an average line showing the self-diffusion coefficient of a molecular group with improved accuracy compared to the average line shown in Fig. 4B, which was calculated using a general method. Thus, the method for calculating the diffusion coefficient according to this embodiment makes it possible to calculate the diffusion coefficient of a molecular group (representative value of the diffusion coefficient) while suppressing variations in the motion of individual molecules.

[0045] <Functional Configuration> The functional configuration of the information processing system 1 according to this embodiment will be described. Fig. 6 is a functional configuration diagram of an example of the information processing system 1 according to this embodiment. Note that the configuration diagram in Fig. 6 appropriately omits portions that are not necessary for explaining this embodiment.

[0046] 6 includes a request receiving unit 20, a response transmitting unit 22, a molecular dynamics calculation unit 24, a mean square displacement calculation unit 26, a diffusion coefficient calculation unit 28, a fitting unit 30, a diffusion coefficient determination unit 32, a display control unit 34, and a storage unit 40. The client terminal 12 of the information processing system 1 includes an information display unit 50, an operation accepting unit 52, a request transmitting unit 54, and a response receiving unit 56.

[0047] The information display unit 50 displays a screen for accepting information input from a worker and information on the execution results of processing by the server device 10 on the display device 502. The operation accepting unit 52 accepts operations by the worker, such as input of information. The request sending unit 54 sends a processing request to the server device 10 in response to the information input from the worker. In addition, the response receiving unit 56 receives a response to the processing request sent by the request sending unit 54 from the server device 10.

[0048] The request receiving unit 20 receives a processing request from the client terminal 12. The response sending unit 22 responds to the client terminal 12 with the execution result of the processing in response to the processing request. The molecular dynamics calculation unit 24 calculates the motion of each individual molecule included in the molecular group using molecular dynamics calculation. The mean square displacement calculation unit 26 calculates the mean square displacement of each individual molecule.

[0049] The diffusion coefficient calculation unit 28 calculates a diffusion coefficient for each molecule based on the calculated mean square displacement for each molecule. The fitting unit 30 fits the cumulative probability of the calculated diffusion coefficient for each molecule with a cumulative distribution function. For example, the fitting unit 30 plots the cumulative probability of the diffusion coefficient for each calculated molecule, as shown in FIG. 5A. The fitting unit 30 regresses the curve of the diffusion coefficient for each molecule obtained, as shown in FIG. 5A, using the cumulative distribution function.

[0050] The diffusion coefficient determination unit 32 determines the diffusion coefficient of the molecular group based on the fitted cumulative distribution function. The diffusion coefficient determination unit 32 determines the diffusion coefficient of the molecular group based on the regressed cumulative distribution function as shown in FIG. 5A , for example. The display control unit 34 controls the display of the client terminal 12. The storage unit 40 stores programs and data necessary for processing executed by the server device 10 or the client terminal 12.

[0051] 6 is an example, and various configurations are possible. For example, the storage unit 40 may be a storage device, a computer, a cloud storage, or the like that is capable of data communication with the server device 10 and the client terminal 12 via, for example, the communication network 18.

[0052] <Processing> As an example of a method according to the present embodiment for determining the diffusion coefficient, an example will be described below in which the self-diffusion coefficient of a lubricant molecule group constituting the lubricant layer of a magnetic recording medium is calculated using molecular dynamics calculations. For example, the lubricant layer of a magnetic recording medium is formed by applying a lubricant to the surface of a protective layer formed on the magnetic recording layer using carbon or the like.

[0053] For example, to simulate the lubricating layer of a magnetic recording medium, a structural model of the lubricant molecules (hereinafter referred to as the lubricant molecular model) and a structural model of the protective layer (hereinafter referred to as the protective layer model) are created, and any number of lubricant molecular models are laid out on top of the protective layer model, thereby reproducing the situation in which a lubricating layer is formed on top of the protective layer.

[0054] FIG. 7 is a flowchart showing an example of the processing procedure of the information processing system 1 according to this embodiment. In step S10, the molecular dynamics calculation unit 24 performs the following calculation of the atomic arrangement. The molecular dynamics calculation unit 24 constructs a model of the lubricant molecules constituting the lubricant layer and the protective layer. The lubricant molecules used in the magnetic recording medium include, for example, perfluoroether chains (-CF ２Examples of such compounds include compounds having a polar group such as a hydroxy group at the end of a fluoropolymer having a repeating structure containing a hydroxyl group (-). The molecular weight of such compounds may be, for example, about 1,000 to 10,000. For example, the following chemical formula (2) represents an example of a lubricant molecule calculated in this embodiment. The polymer of chemical formula (2) is a chain polymer. Alternatively, the polymer may be represented by chemical formula (3).

[0055] R1-X-R2 (2) R1-X-R3-X-R2 (3) In chemical formulas (2) and (3), X is a main chain portion containing a repeating structure. R1 and R2 are a first terminal portion and a second terminal portion, respectively, and have at least one polar group, typically a hydroxyl group. The structures of R1 and R2 may be the same or different. R3 is a linking portion. R3 has the same characteristics as R1 and R2.

[0056] The above molecule is structurally optimized using quantum chemical calculations to produce a lubricant molecular model. This lubricant molecular model contains information on the molecular structure and the charge of each atom, and can therefore be used appropriately in molecular dynamics calculations.

[0057] The protective layer is a layer for protecting the recording layer. The protective layer is composed of carbon atoms or silicon carbide. The unit structure of the layer composed of carbon atoms can be a unit structure of graphene or diamond carbon. The graphene or diamond carbon structure is preferably doped with oxygen, nitrogen, or the like. This is because using these as adsorption sites can strengthen the bond with the polar group of the lubricant. For example, the protective layer of a graphene structure has a minimum unit consisting of six carbon atoms as its "unit structure." The protective layer may be composed of a thickness of one atom or a layer of multiple atoms.

[0058] The protective layer model is created by optimizing the unit structure of the protective layer using quantum chemical calculations, and then repeating this optimized unit structure in the planar direction within the range of the periodic boundary cell used in the molecular dynamics calculations described below. This protective layer model has information on the structure and the charge of each atom, so it can be used appropriately in the molecular dynamics calculations.

[0059] The initial model of the lubricant layer (initial model of the lubricant layer) is constructed using the lubricant molecular model and protective layer model created as described above. The initial model of the lubricant layer for simulating the lubricant layer of a magnetic recording medium can be constructed by constructing the lubricant molecular model on the protective layer model with a certain degree of uniformity.

[0060] The initial lubricant model is preferably constructed in a periodic boundary cell large enough to accommodate approximately 10 to 1000 lubricant molecules. As a method for arranging the lubricant molecules in the initial lubricant model, the molecules may be arranged near the protective layer model so that they do not overlap, or a stabilized initial arrangement may be prepared using molecular dynamics calculations or the like.

[0061] In step S12, the molecular dynamics calculation unit 24 assigns an identifier to each lubricant molecule in the initial model of the lubricant layer. In step S14, the molecular dynamics calculation unit 24 performs a molecular dynamics calculation using the constructed initial model of the lubricant layer. The mean square displacement calculation unit 26 calculates the mean square displacement of each lubricant molecule in the initial model of the lubricant layer from the results of the molecular dynamics calculation.

[0062] For example, molecular dynamics calculations can be performed under the following conditions. Note that the conditions for the molecular dynamics calculations are not limited to the following: Cell size: 96 Å × 84 Å × 150 Å (periodic boundary cell) Tracking time: 6 ns (time per step: 2 fs, total number of steps: 3 million) Temperature: 300 K (assumed to be room temperature) Molecular force field: GAFF force field Coulomb interaction calculation method: Particle-Particle Particle-Mesh Ewald method In step 16, the diffusion coefficient calculation unit 28 uses the following equation (2) to calculate the self-diffusion coefficient for each individual lubricant molecule based on the mean square displacement for each individual lubricant molecule of the initial lubricant layer model calculated from the results of the molecular dynamics calculation for the tracking time T.

[0063] In addition, t ０ is the initial time. r(t) is the position of the center of mass of the lubricant molecule at time t.

[0064] In step S18, the diffusion coefficient calculation unit 28 selects a physically appropriate self-diffusion coefficient from the self-diffusion coefficients for each individual lubricant molecule calculated in step S16. The process of step S18 is a process of excluding the self-diffusion coefficients of molecules that have moved so that the self-diffusion coefficient cannot be properly determined. For example, if the mean square displacement is convex, the slope of the regression line will be close to 0 or negative, resulting in a physically inappropriate self-diffusion coefficient. Therefore, the diffusion coefficient calculation unit 28 selects a physically appropriate self-diffusion coefficient by setting a lower limit for the value of the self-diffusion coefficient used in the processes from step S20 onwards.

[0065] In step S20, the fitting unit 30 plots the cumulative probability of the self-diffusion coefficient for each individual lubricant molecule selected in step S18 as a physically reasonable self-diffusion coefficient, for example, as shown in FIG. 5A.

[0066] In step S22, the fitting unit 30 selects and fits an appropriate cumulative distribution function for the cumulative probability of the self-diffusion coefficient plotted in step S20. For example, the fitting unit 30 fits the ln(SDC) of the self-diffusion coefficient for each lubricant molecule based on an error function or a complementary error function.

[0067] In step S24, the diffusion coefficient determination unit 32 determines the diffusion coefficient of the lubricant molecule group based on the cumulative distribution function fitted in step S22. For example, the diffusion coefficient determination unit 32 can determine the diffusion coefficient of the lubricant molecule group based on the regressed cumulative distribution function as shown in FIG. 5A.

[0068] There is a correlation between the lubricity value measured in an experiment and the self-diffusion coefficient of the lubricant molecule group of the lubricant layer calculated by the method of this embodiment for determining the diffusion coefficient. Therefore, the self-diffusion coefficient of the lubricant molecule group of the lubricant layer calculated by the method of this embodiment can be used as an index of the lubricity of the lubricant layer. Specifically, for molecules whose lubricity values ​​have been measured in an experiment, the lubricity of the lubricant layer can be relatively evaluated based on the self-diffusion coefficient of the lubricant molecule group of the lubricant layer calculated by the method of this embodiment.

[0069] Therefore, in the information processing system 1 according to this embodiment, the performance of the lubricant layer can be evaluated based on the self-diffusion coefficient of the lubricant molecule group in the lubricant layer calculated by the method according to this embodiment.

[0070] As described above, the information processing system 1 according to this embodiment can provide an information processing device, an information processing method, and a program that improve the accuracy of the diffusion coefficient of a molecular group calculated using molecular dynamics calculations.

[0071] <Supplementary Explanation> In this embodiment, the reason for fitting cumulative probability instead of distribution is that if a distribution is used, a regression curve cannot be uniquely determined, and cumulative probability is used to avoid this. To find the distribution, a range within which the distribution is taken is specified for the diffusion coefficient, and the number of divisions into which that range is to be divided is determined. Furthermore, for each divided region, the number of molecules having a diffusion coefficient within that range is counted and used as a data point. At this time, the range specification and division method can be arbitrarily determined. These setting methods change the shape of the distribution, which can ultimately affect the regression curve.

[0072] The cumulative distribution function is the probability that a random variable will be equal to or less than a certain value (x). Therefore, the cumulative distribution function may be arbitrarily determined depending on the problem. In this embodiment, the cumulative probability plotted by taking the logarithm of the diffusion coefficient is regressed based on the error function (or complementary error function).

[0073] As an example of diffusion coefficient analysis, a nitrogen-doped carbon slab model was created, with approximately 30-50 molecules with a molecular weight of 1,000 or more randomly adsorbed on its surface. The atomic positions of the carbon slab were fixed, and molecular dynamics calculations were performed to determine the diffusion coefficient of the molecular group. As a condition for the molecular dynamics calculation, the interactions between atoms were described using the Gaff force field, and the charge of each atom was determined using quantum chemical calculations.

[0074] The temperature was 300 K, the time was 6 ns, and the time step was 2 fs. For one diffusion coefficient analysis, three molecular dynamics calculations were performed under the same conditions. Steps S10 to S18 were performed for each trial of the molecular dynamics calculation, and from step S20 onwards, the diffusion coefficients for each molecule obtained in each trial were used together.

[0075] The calculations in the above examples are based on a model in which the diffusion coefficient for each molecule is likely to vary. The calculations in the above examples are characterized by determining surface diffusion and the diffusion coefficient of a group of polymers. It is known that surface diffusion results in greater diffusion of surface molecules and atoms than bulk diffusion (diffusion within a solid).

[0076] In the calculations in the above examples, the polar groups of the molecules are adsorbed to the N atoms on the carbon layer, and the molecules diffuse by changing their adsorption positions. Multiple polar groups exist within a molecule, and adjacent molecules interact with each other. Therefore, there are more modes of diffusion than with atoms or small molecules, and the diffusion coefficients for each molecule vary greatly.

[0077] [Other Embodiments] The server device 10 according to the present embodiment may be configured such that a plurality of computers cooperate to perform the above-described processing. For example, the server device 10 according to the present embodiment may be configured such that the server device 10 cooperates with the client terminal 12 to perform the above-described processing.

[0078] The diffusion coefficient of the molecule group calculated in this embodiment can be used to control, for example, manufacturing equipment that produces magnetic recording media such as HDDs by specifying the lubricant molecule group that constitutes the lubricant layer of the magnetic recording medium.

[0079] The information processing system 1 according to the present embodiment can improve the accuracy of the diffusion coefficient of a molecular group calculated using molecular dynamics calculations. The diffusion coefficient of a molecular group calculated with high accuracy by the information processing system 1 according to the present embodiment can be used, for example, to control a manufacturing device for a magnetic recording medium.

[0080] Although the present embodiment has been described above, it will be understood that various modifications in form and details are possible without departing from the spirit and scope of the claims. While the present invention has been described above based on examples, the present invention is not limited to the above examples and various modifications are possible within the scope of the claims. This application claims priority from basic application No. 2023-137135, filed with the Japan Patent Office on August 25, 2023, the entire contents of which are incorporated herein by reference.

[0081] REFERENCE SIGNS LIST 1 Information processing system 10 Server device 12 Client terminal 18 Communication network 24 Molecular dynamics calculation unit 26 Mean square displacement calculation unit 28 Diffusion coefficient calculation unit 30 Fitting unit 32 Diffusion coefficient determination unit

Claims

1. An information processing device comprising: a molecular dynamics calculation means for calculating the motion of a molecular group including at least one of atoms and molecules using molecular dynamics calculation; a mean square displacement calculation means for calculating a mean square displacement for each of the atoms and molecules; a diffusion coefficient calculation means for calculating a diffusion coefficient for each of the atoms and molecules based on the mean square displacement for each of the atoms and molecules; a fitting means for fitting a cumulative probability of the diffusion coefficient with a cumulative distribution function; and a diffusion coefficient determination means for determining a diffusion coefficient of the molecular group based on the fitted cumulative distribution function.

2. The information processing device according to claim 1, wherein said diffusion coefficient determining means determines a representative value of the diffusion coefficient of said molecular group using said fitted cumulative distribution function.

3. The information processing device according to claim 1 or 2, wherein the cumulative distribution function is an error function or a complementary error function.

4. The information processing device according to any one of claims 1 to 3, wherein the diffusion coefficient of the molecular group is a diffusion coefficient of a polymer group that diffuses on a surface.

5. The information processing device according to any one of claims 1 to 4, wherein the molecular group is a lubricant molecular group that constitutes a lubricant layer of a magnetic recording medium.

6. An information processing method in which an information processing device performs the following steps: a molecular dynamics calculation step of calculating the motion of a molecular group including at least one of atoms and molecules using molecular dynamics calculation; a mean square displacement calculation step of calculating a mean square displacement for each of the atoms and molecules; a diffusion coefficient calculation step of calculating a diffusion coefficient for each of the atoms and molecules based on the mean square displacement for each of the atoms and molecules; a fitting step of fitting a cumulative probability of the diffusion coefficient with a cumulative distribution function; and a diffusion coefficient determination step of determining a diffusion coefficient of the molecular group based on the fitted cumulative distribution function.

7. A program for causing an information processing device to execute the following steps: a molecular dynamics calculation step for calculating the motion of a molecular group including at least one of atoms and molecules using molecular dynamics calculation; a mean square displacement calculation step for calculating a mean square displacement for each of the atoms and molecules; a diffusion coefficient calculation step for calculating a diffusion coefficient for each of the atoms and molecules based on the mean square displacement for each of the atoms and molecules; a fitting step for fitting a cumulative probability of the diffusion coefficient with a cumulative distribution function; and a diffusion coefficient determination step for determining a diffusion coefficient of the molecular group based on the fitted cumulative distribution function.

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