Lubricant layer performance evaluation method

Abstract

A method for evaluating the performance of a lubricating layer according to the present invention comprises: a step for preparing a lubricant molecule model and a protective layer model by using a quantum chemical calculation; a step for performing a molecular dynamics calculation of an initial lubricating layer model constructed from the lubricant molecule model and the protective layer model; and a step for calculating an index of the adsorption degree of a lubricant molecule to a protective layer, from the results of the molecular dynamics calculation.

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the performance of a lubricating layer. [Background technology]

[0002] To improve the recording density of magnetic recording / reproducing devices such as hard disk drives, it is necessary to reduce the flying height of the magnetic head. Therefore, there is a need to further reduce the thickness of the lubricating layer formed as the outermost layer on the protective layer of the magnetic recording medium. Currently, the thickness has reached 10 Å or less, which is as thin as a monolayer.

[0003] The performance of the lubricating layer of a magnetic recording medium, which has reached a thickness equivalent to that of a monolayer, is affected by differences in the microstructure of the lubricant molecules that make up the lubricating layer. For this reason, microscale simulations focusing on the microstructure of lubricant molecules using molecular dynamics calculations and quantum mechanical calculations have been carried out, and lubricant molecules have been proposed (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-168512 [Patent Document 2] International Publication No. 2018 / 159232 Summary of the Invention [Problem to be solved by the invention]

[0005] The performance of a lubricating layer is defined by macroscopic phenomena such as lubrication and floating. These phenomena are observed in experiments, and performance such as lubrication and floating is evaluated based on the observation results. Therefore, simulations that handle lubricating layers must be able to predict and quantify these macroscopic phenomena.

[0006] For example, Patent Document 1 conducts a simulation of a state in which one lubricant molecule is adsorbed onto the surface of a protective film, and suggests a reduction in the surface energy of the lubricant layer based on the orientation of the polar group of the lubricant molecule.

[0007] On the other hand, in Patent Document 2, a simulation was carried out assuming that a lubricant layer was formed on the outermost surface of a magnetic recording medium, where multiple molecules were handled under periodic boundary conditions, and the film thickness and coverage of the lubricant layer were simulated from this simulation.

[0008] However, neither Patent Document 1 nor Patent Document 2 describes or suggests lubrication performance and flying performance, which are considered to be important properties in the current development of lubricant layer molecules.

[0009] The present invention has been made in view of the above circumstances, and provides a method for evaluating the performance of a lubricating layer, which is capable of evaluating the performance of the lubricating layer. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the performance of the lubricating layer can be predicted by carrying out the simulation described below.

[0011] [1] A step of preparing a lubricant molecular model and a protective layer model using quantum chemical calculations; performing a molecular dynamics calculation of an initial model of the lubricant layer constructed from the lubricant molecular model and the protective layer model; calculating an index of the degree of adsorption of lubricant molecules to the protective layer from the results of the molecular dynamics calculation; A method for evaluating the performance of a lubricating layer, comprising: [2] preparing a lubricant molecular model and a protective layer model using quantum chemical calculations; performing a molecular dynamics calculation of an initial model of the lubricant layer constructed from the lubricant molecular model and the protective layer model; calculating an index of the degree of lubrication of the lubricant molecules on the protective layer from the results of the molecular dynamics calculation; A method for evaluating the performance of a lubricating layer, comprising: [3] A method for evaluating the performance of a lubricating layer, which evaluates the performance of a lubricating layer based on two indexes: the index of the degree of adsorption calculated in [1] and the index of the degree of lubrication calculated in [2]. [4] The protective layer is a protective layer formed on the surface of the magnetic recording medium, The method for evaluating the performance of a lubricating layer according to any one of [1] to [3], wherein the lubricant molecules are lubricant molecules for a magnetic recording medium. [Effects of the Invention]

[0012] According to the above aspect of the present invention, the performance of the lubricating layer can be evaluated by simulating a lubricating layer model using molecular dynamics calculations and evaluating the adsorption or lubricity of the lubricant molecules from the calculated results. This makes it possible to select lubricant molecules capable of forming a lubricating layer that has performance that meets the development targets for flying performance or lubrication performance without conducting experiments. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram showing a unit structure of a protective layer. [Figure 2] This is a diagram showing the flow of the coating simulation. Figure 2(a) shows only the protective layer, Figure 2(b) shows the protective layer with lubricant molecules randomly arranged on it, Figure 2(c) shows the progress of the coating simulation, and Figure 2(d) shows the completed initial model of the lubricant layer after the coating simulation is complete. [Figure 3] FIG. 10 is a scatter plot showing both Nabs and self-diffusion coefficients of the simulation results. [Figure 4] FIG. 10 is a scatter diagram showing the correlation between simulation results and experimental results, and is a diagram showing a comparison between Nabs and levitation test results. [Figure 5] FIG. 1 is a scatter diagram showing the correlation between simulation results and experimental results, and a diagram showing a comparison of the self-diffusion coefficient and the lubricity test results. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described. In the following embodiments, a method for simulating a lubricant layer model by molecular dynamics calculation and a method for determining the superiority or inferiority of lubricant molecules using the results calculated by this method are disclosed. Note that this embodiment is not limited to the following description and can be modified as appropriate within the scope of the present invention. Furthermore, in this specification, unless otherwise specified, the symbol "to" indicating a numerical range means that the numerical values ​​written before and after it are included as the lower and upper limits.

[0015] One form of a method for evaluating the performance of a lubricant layer according to an embodiment of the present invention includes the steps of constructing a lubricant molecular model and a protective layer model using quantum chemical calculations, performing molecular dynamics calculations on the initial lubricant layer model constructed from the lubricant molecular model and the protective layer model, and calculating an index of the degree of adsorption of the lubricant molecules to the protective layer from the results of the molecular dynamics calculations.

[0016] An example of a target of the evaluation method according to this embodiment is a lubricating layer in which the protective layer is a protective layer formed on the surface of a magnetic recording medium, the lubricant molecules are lubricant molecules for a magnetic recording medium, and the lubricant molecules are prepared using the lubricant molecules.

[0017] A magnetic recording medium has a magnetic recording layer formed on a substrate, a protective layer made of carbon or the like formed on the magnetic recording layer, and a lubricant applied to the surface of the protective layer to form a lubricating layer.

[0018] Therefore, in this embodiment, in order to simulate the lubricating layer of a magnetic recording medium, a structural model of a lubricant molecule (hereinafter referred to as the lubricant molecular model) and a structural model of a protective layer (hereinafter referred to as the protective layer model) are created, and an arbitrary number of lubricant molecular models are laid out on top of the protective layer model to reproduce the situation in which a lubricating layer is formed on a protective layer.

[0019] <Lubricant molecular model and protective layer model construction process> In the evaluation method according to this embodiment, first, a model of the lubricant molecules constituting the lubricant layer and the protective layer is constructed.

[0020] [Lubricant molecular model] Lubricant molecules used in magnetic recording media include, for example, compounds having a polar group such as a hydroxyl group at the end of a fluorine-based polymer having a repeating structure containing a perfluoroether chain (-CF2-), and the molecular weight of such compounds is about 1,000 to 10,000.

[0021] The following general formula (1) represents an example of a fluorine-containing ether compound calculated in this embodiment: This molecule is a chain polymer.

[0022] [ka]

[0023] In formula (1), X represents a main chain portion containing a repeating unit. R1 and R2 represent a first terminal portion and a second terminal portion, respectively, and each have at least one polar group, typically a hydroxyl group. The structures of R1 and R2 may be the same or different.

[0024] Such molecules are structurally optimized using quantum chemical calculations to create a lubricant molecular model. This model contains information on the molecular structure and the charge of each atom, making it suitable for use in molecular dynamics calculations.

[0025] [Protection layer model] The protective layer is a layer for protecting the recording layer and is made of carbon atoms or silicon carbide. The unit structure of the layer made of carbon atoms can be a unit structure of graphene or diamond carbon. It is preferable that the graphene or diamond carbon structure is doped with oxygen, nitrogen, or the like. By using these as adsorption sites, it is possible to strengthen the bond with the polar group of the lubricant.

[0026] For example, the protective layer of a graphene structure has a "unit structure" which is the smallest unit consisting of six carbon atoms.

[0027] The protective layer may be composed of a thickness of one atom or a thickness of multiple atoms.

[0028] The unit structure of such a protective layer is optimized by quantum chemical calculation, and this optimized unit structure is repeated in the planar direction within the range of the periodic boundary cell used in the molecular dynamics calculation described below to form a protective layer model.

[0029] This protective layer model contains information on the structure and the charge of each atom, and can therefore be used appropriately in molecular dynamics calculations.

[0030] <Initial lubrication layer model construction process> In the lubricant layer initial model construction step, an initial model of the lubricant layer (lubricant layer initial model) is constructed using the lubricant molecule model and protective layer model constructed in the previous step.

[0031] The initial lubricant layer model for performing the simulation may be constructed by constructing a lubricant molecule model on a protective layer model with a relatively uniform arrangement. The initial lubricant layer model is preferably constructed in a periodic boundary cell large enough to accommodate 10 to 1000 lubricant molecules.

[0032] As a method for arranging the lubricant molecules in the initial lubricant layer model, the individual molecules may be arbitrarily arranged near the protective layer model so as not to overlap, or a stabilized initial arrangement may be prepared using molecular dynamics calculations or the like.

[0033] <Process for performing molecular dynamics calculation> In the step of performing molecular dynamics calculations, the molecular dynamics calculations are performed using the initial lubricant layer model constructed in the initial lubricant layer model construction step.

[0034] For example, molecular dynamics calculations can be performed under the following conditions: Note that the conditions for molecular dynamics calculations are not limited to the following. Cell size: 96Å×84Å×150Å (periodic boundary cell) Tracking time: 6ns (1 step time: 1ps, total number of steps: 6 million) Temperature: 300K (assuming room temperature) ·Molecular force field: GAFF force field Coulomb interaction calculation method: Particle-Particle Particle-Mesh Ewald method

[0035] <Step of calculating the index of the degree of adsorption> Lubricant molecules are adsorbed through the interaction between the polar groups in the molecule and the adsorption sites on the protective layer model. Therefore, for a given adsorption group in a lubricant molecule, the state in which it is sufficiently close to the surface of the protective layer model is defined as "adsorbed to the protective layer."

[0036] A method for calculating an index of the degree of adsorption of a lubricant layer composed of lubricant molecules having a plurality of adsorption groups i (hereinafter also referred to as adsorption groups A, B, C, . . . ) will be described below.

[0037] In the molecular dynamics calculation, the shape of the lubricant molecule and the positions of the atoms that make up the lubricant molecule are tracked as they change over time.

[0038] The proportion of adsorbable groups A in the lubricant molecules that are in an adsorbed state in the entire lubricant layer at a certain time t can be described by the following formula (I): Adsorption ratio of adsorbed group A = number of adsorbed groups A / total number of lubricant molecules (I)

[0039] The time average of the calculated adsorption rate of adsorption group A is taken as the adsorption probability of adsorption group A on the lubricant molecule.

[0040] By following the same procedure, the adsorption probability is calculated for adsorption groups B, C, etc., and for all adsorption groups.

[0041] The sum of the adsorption probabilities of these adsorption groups is taken as the net number of adsorption groups adsorbed to the protective layer on one lubricant molecule.

[0042] This net number is used as an index Nabs of the degree of adsorption of the lubricating layer. That is, the index Nabs is expressed by the following formula (II).

[0043]

number

[0044] As will be described later in the Examples, there is a correlation between the index of the degree of adhesion of the lubricant layer and the value of the flying performance measured in an experiment. Therefore, it is possible to select lubricant molecules that can form a lubricant layer with good flying performance based on the index of the degree of adhesion calculated from the lubricant layer simulation. Specifically, as will be shown in the Examples described later, the degree of adhesion of the lubricant molecules is evaluated relatively based on the index of the degree of adhesion calculated for molecules with clear experimental results.

[0045] Another form of the lubricant performance evaluation method according to this embodiment includes the steps of constructing an initial lubricant layer model including a lubricant molecular model and a protective layer model using quantum chemical calculations, performing molecular dynamics calculations on the initial lubricant layer model, and calculating an index of the degree of lubrication of the lubricant molecules to the protective layer from the results of the molecular dynamics calculations.

[0046] The lubricant molecular model and protective layer model construction process, the lubricant layer initial model construction process, and the construction process using molecular dynamics calculations are carried out in the same manner as the processes included in the lubricant evaluation method according to the present embodiment described above.

[0047] <Step of calculating the index of lubrication degree> The lubricity of the lubricant molecules is determined by calculating the self-diffusion coefficient of the lubricant molecules obtained as a result of molecular dynamics calculations, and this is used as an index of the degree of lubrication of the lubricant layer.

[0048] From the molecular dynamics calculations for the tracking time T, the self-diffusion coefficient D of the target lubricant molecule is calculated by the following equation (III): where t0 is the initial time, and r(t) is the position of the center of gravity of the molecule at time t.

[0049]

number

[0050] As will be described later in the examples, there is a correlation between the lubricity value measured in an experiment and the self-diffusion coefficient value of the lubricant molecule calculated from the lubrication layer simulation. Therefore, the self-diffusion coefficient calculated from the lubrication layer simulation is used as an index of the lubricity of the lubrication layer. Specifically, as will be described later in the examples, for molecules whose lubricity value has been measured in an experiment, the lubricity of the lubrication layer is relatively evaluated based on the calculated index of the lubrication degree.

[0051] The method for evaluating the performance of a lubricating layer according to this embodiment can also evaluate the performance of the lubricating layer based on two indices: the adsorption degree index and the lubrication degree index. In this case, as in the examples described later, the performance of the lubricating layer can be relatively evaluated based on the adsorption degree and the lubrication degree index calculated for molecules with clear experimental results. [Example]

[0052] The present embodiment will be specifically described below with reference to examples, but the present embodiment is not limited to the following examples.

[0053] [lubricant molecule] As the main chain portion X in the above-mentioned general formula (1), the following general formula (2) or (3) was used.

[0054] [ka] (In general formula (2) and general formula (3), m and n represent integers of 1 to 30.)

[0055] The following structures were used as the first terminal group R1 and the second terminal group R2 in the above general formula (1).

[0056] [ka] (In general formula (4), a represents an integer of 1 to 3, and b represents an integer of 0 to 10. In general formula (5), c represents an integer of 1 to 3, and d represents an integer of 0 to 10. In general formula (6), e represents an integer of 1 to 3. In general formula (7), f represents an integer of 1 to 3. In general formula (8), g represents an integer of 1 to 3.)

[0057] The following simulation was carried out for a plurality of lubricant molecules each composed of a combination of a main chain portion X, a first terminal group R1, and a second terminal group R2 as shown in Table 1.

[0058] [simulation] (protective layer) Figure 1 is a schematic diagram illustrating the structure of the protective layer used in the simulation. As shown in Figure 1, two layers of nitrogen-doped graphene were used as the protective layer in the simulation. Here, dark circles 30 represent nitrogen atoms, and light circles 31 represent carbon atoms. Periodic boundary conditions were set in which the unit structure of each nitrogen-doped graphene was repeated infinitely in the planar direction. The arrows in Figure 1 indicate the planar direction in which the unit structure is repeated. In each nitrogen-doped graphene, some of the carbon atoms in graphene were replaced with nitrogen atoms. The proportion of nitrogen atoms in each nitrogen-doped graphene was set to 12.5% ​​(by number).

[0059] [Construction of lubricant molecular model and protective layer model] The stable structures and the charge of each atom were determined for the lubricant molecules and the unit structure of the protective layer described above by quantum chemical calculations. After performing structural optimization to calculate the stable structures, the atomic charges in the structures were calculated.

[0060] The stable structure of the lubricant molecule was calculated using the B3LYP / 6-31G density functional theory parameter / basis set combination.* The atomic charges in the determined stable structure were calculated using the Minimal Basis set Mulliken population analysis. The stable structure of the protective layer was calculated using the HSEH1PBE / 6-31G density functional theory parameter / basis set combination. * The atomic charges in the determined stable structure were calculated by Mulliken population analysis. These quantum chemical calculations were performed using the Gaussian (registered trademark) 16 program package from Gaussian Corporation.

[0061] <Process for performing molecular dynamics calculation> The process of performing molecular dynamics calculations consists of two steps: a preparatory calculation (hereinafter referred to as lubricant application simulation) in which a lubricant molecular model is placed on top of the protective layer model and an initial lubricant layer model is constructed, and an actual calculation (hereinafter referred to as lubricant layer simulation) in which the movement of the actual lubricant layer is tracked from the constructed initial lubricant layer model.

[0062] [Lubricant application simulation] Using the lubricant molecular model and protective layer model containing the structure and the charge information of each atom created as described above, an initial lubricant layer model was constructed as the initial structure for the lubricant layer simulation. In this example, a lubricant application simulation was performed to reproduce the state in which the lubricant layer covers the protective layer at room temperature (300 K).

[0063] The lubricant application simulation conditions were set as follows: The GAFF force field was used as the molecular force field, and the depth parameter value of the Lennard-Jones potential between the protective layer and the lubricant layer was scaled by 1 / 2 to match the results of quantum chemical calculations (the ε parameter was halved). The cutoff method was also used for the Lennard-Jones interaction. The cutoff distance was set to 12 Å, at which the interaction can be considered negligible. The velocity scaling method was used as the temperature control method, and simulations were performed using an NVT ensemble with constant particle number (N), volume (V), and temperature (T). The free software OCTA's COGNAC engine was used for molecular dynamics calculations.

[0064] 2(a) to 2(d) are schematic diagrams for explaining a simulation of lubricant application. In Fig. 2(a) to 2(d), reference numeral 1a denotes lubricant molecules, reference numeral 1b denotes a lubricant layer, and reference numeral 20 denotes a protective layer.

[0065] First, as shown in Fig. 2(a), unit structures of the protective layer stabilized by quantum chemical calculations were placed in a periodic boundary cell of 96 Å × 84 Å × 150 Å to form the protective layer 20. The atomic positions of the protective layer were fixed during the simulation, as they were assumed not to change.

[0066] Next, as shown in Figure 2(b), lubricant molecules 1a were randomly arranged above the surface of protective layer 20. In the experiment, a thin lubricant layer with a thickness of about 9 Å was created and its physical properties were measured. To compare the physical properties with those of the lubricant layer 1b, the number of lubricant molecules 1a was adjusted so that the film thickness at thermal equilibrium at room temperature would be about 9 Å when lubricant layer 1b was formed.

[0067] 2(c) and 2(d), a downward force was applied to the hydrogen atom located at the end of the lubricant molecule 1a, and molecular dynamics calculations were performed at room temperature of 300 K to cause the lubricant molecule 1a to descend, forming a lubricant layer 1b on the surface of the protective layer 20, which was used as an initial lubricant layer model. Here, FIG. 2(c) shows the structure during the calculation, and FIG. 2(d) shows the structure of the lubricant layer 1b after 30 ps of calculation.

[0068] <Molecular dynamics calculation (lubricant layer simulation)> The lubricant simulation used the GAFF force field as the molecular force field. The depth parameter of the Lennard-Jones potential between the protective layer and the lubricant layer was scaled by half (the ε parameter was halved) to match the results of quantum chemical calculations. The cutoff method was used for the Lennard-Jones interaction. The cutoff distance was set to 12 Å, which is considered negligible. The particle-particle particle-mesh Ewald method was used to calculate the long-range Coulomb interaction. The velocity scaling method was used as the temperature control method, and simulations were performed using an NVT ensemble with constant particle number (N), volume (V), and temperature (T). The free software LAMMPS was used for molecular dynamics calculations.

[0069] In the lubricant layer simulation, the structure and behavior of the lubricant layer in a thermal equilibrium state at 300K were reproduced and analyzed.

[0070] To reach thermal equilibrium at room temperature in a short time, a simulation was first performed for 6 ns under high-temperature conditions at 400 K, followed by a simulation in which the temperature was gradually lowered from 400 K to 300 K over 1 ns. After that, a simulation for 6 ns was performed under temperature conditions at 300 K to reproduce the structure of the lubricant layer at room temperature and track its behavior. It was confirmed that in each simulation of the lubricant molecules shown in Table 1, thermal equilibrium was reached sufficiently in about 3 ns.

[0071] <Calculation of each performance index> The index of the degree of adsorption of the lubricating layer and the index of the degree of lubrication were calculated.

[0072] [Calculation of adsorption index] The index Nabs of the degree of adsorption of the lubricating layer was calculated by the method described above.

[0073] Here, the distance between the protective layer and the adsorption group in the "sufficiently close" state was set to 2 Å or less for hydroxyl groups, and 3 Å or less for amino and nitrile groups.

[0074] [Calculation of lubrication index] As shown in the embodiment, the self-diffusion coefficient of the lubricant molecules was calculated and used as an index of the degree of lubrication. The self-diffusion coefficient was calculated using the displacement of the lubricant molecules in a simulation at 300 K for 6 ns.

[0075] The calculated structure of the lubricant layer and the calculation results for its adsorption index (Nabs) and lubricity index (self-diffusion coefficient) are shown in Table 1. Here, Simulation No. 4 is a lubricant molecule that serves as the standard for adsorption. Lubricant molecules with Nabs greater than No. 4 are lubricant molecules that can form a lubricant layer with better adsorption. Simulation No. 3 is a lubricant molecule that serves as the standard for lubricity. Lubricant molecules with a self-diffusion coefficient greater than No. 3 are lubricant molecules that can form a lubricant layer with better lubricity.

[0076] [Table 1]

[0077] A scatter plot showing both Nabs and the self-diffusion coefficient is shown in Figure 3. The vertical axis represents Nabs, and the horizontal dashed line represents the reference result for No. 4. The horizontal axis represents the self-diffusion coefficient, and the vertical dashed line represents the reference result for No. 3.

[0078] From the above simulation results, it can be predicted that, for example, a lubricating layer made using lubricant No. 15 will have excellent adsorption properties, and a lubricating layer made using lubricant No. 9 will have excellent lubricity. In addition, it can be predicted that No. 7, which has both Nabs and a self-diffusion coefficient that exceed the standard values, will be able to form a lubricating layer that excels in both properties.

[0079] For magnetic recording media including a lubricating layer using the above-mentioned lubricant molecules, a flyability test and a lubricity test were conducted using conventional methods. The results are shown in Table 2. Note that the same lubricant molecules were used for experiments with the same experiment number in Table 2 and simulation number in Table 1.

[0080] [Table 2]

[0081] 4 and 5 show scatter diagrams comparing the calculation results with the corresponding experimental evaluation values.

[0082] Figure 4 shows the relationship between the evaluation value of the buoyancy test and Nabs calculated by simulation. In Figure 4, a linear regression equation was obtained, and the coefficient of determination R 2 was approximately 0.6728, which confirmed that there was a sufficient correlation between buoyancy and Nabs, and that Nabs could be used to determine the superiority or inferiority of buoyancy.

[0083] Figure 5 shows the relationship between the evaluation value of the lubricity test and the self-diffusion coefficient calculated by simulation. In Figure 5, a linear regression equation was obtained, and the coefficient of determination R 2 was approximately 0.8071, which confirmed that there is a sufficient correlation between lubricity and the self-diffusion coefficient, and that the self-diffusion coefficient can be used to determine the superiority or inferiority of lubricity.

[0084] From the above, it was confirmed that the flying characteristics and lubricity of the lubricating layer can be predicted with sufficient reliability from the simulation results.

[0085] Although the embodiments of the present invention have been described above, the above embodiments are presented as examples, and the present invention is not limited to the above embodiments. Various combinations, omissions, substitutions, modifications, etc. are possible within the scope of the gist of the present invention described in the claims. These embodiments and their modifications are included in the scope and gist of the present invention, and are also included in the scope of the inventions described in the claims and their equivalents.

[0086] This application claims priority based on Japanese Patent Application No. 2020-174602, filed with the Japan Patent Office on October 16, 2020, the entire contents of which are incorporated herein by reference. [Industrial Applicability]

[0087] The method for evaluating the performance of a lubricating layer can be suitably used as a method for evaluating the performance of a lubricating layer used in a magnetic recording medium or the like. [Explanation of symbols]

[0088] 30 nitrogen atoms 31 carbon atoms 1a Lubricant molecule 1b Lubricant layer 20 protective layer

Claims

1. preparing a lubricant molecular model and a protective layer model using quantum chemical calculations; performing a molecular dynamics calculation of an initial model of the lubricant layer constructed from the lubricant molecular model and the protective layer model; calculating an index of the degree of adsorption of lubricant molecules to the protective layer from the results of the molecular dynamics calculation; calculating an index of the degree of lubrication of the lubricant molecules on the protective layer from the results of the molecular dynamics calculation; a step of evaluating the floating performance of the lubricating layer as a performance of the lubricating layer based on the calculated index of the degree of adsorption, and evaluating the lubricity of the lubricating layer as a performance of the lubricating layer based on the calculated index of the degree of lubrication; Including, The indicator of the degree of adsorption is The proportion of one of the plurality of adsorbing groups in the lubricant molecules that is in an adsorbed state at a certain time in the entire lubricant layer that is composed of the lubricant molecules having a plurality of adsorbing groups is calculated using the following formula (I): Adsorption ratio of one adsorption group = number of one adsorption group in an adsorbed state / total number of lubricant molecules (I) The time average of the calculated adsorption rate of the one adsorption group is defined as the adsorption probability of the one adsorption group on the lubricant molecule; calculating the adsorption probability of the other adsorbing groups among the plurality of adsorbing groups for each type of the adsorbing group; The sum of the adsorption probabilities of the adsorption groups is defined as the net number of adsorption groups adsorbed to the protective layer that one lubricant molecule has, and A method for evaluating the performance of a lubricating layer, wherein the net number is used as an index of the degree of adsorption of the lubricating layer.

2. A method for evaluating the performance of a lubricating layer as described in claim 1, wherein the index of the degree of lubrication is calculated by using the self-diffusion coefficient of the target lubricant molecule according to the following formula (III). [Equation 1] (Note that in formula (III), t 0 is the initial time, and r(t) is the position of the center of gravity of the molecule at time t.)

3. the protective layer is formed on the surface of the magnetic recording medium, 3. The method for evaluating the performance of a lubricant layer according to claim 1, wherein the lubricant molecules are lubricant molecules for a magnetic recording medium.

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