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Article

Molecular Dynamics Study on the Molar Ratio-Dependent Interaction Regulation Mechanisms in CL-20/FOX-7 Energetic Cocrystal Explosives

by
Ruikang Zheng
,
Yuling Wang
,
Tao Wang
*,
Shuchang Li
,
Yibo Luo
,
Xingyu Liu
,
Kaizeng Quan
and
Shusheng Zhang
School of Nuclear Engineering, Rocket Force University of Engineering, Xi’an 710025, China
*
Author to whom correspondence should be addressed.
Crystals 2025, 15(11), 912; https://doi.org/10.3390/cryst15110912 (registering DOI)
Submission received: 9 September 2025 / Revised: 7 October 2025 / Accepted: 18 October 2025 / Published: 22 October 2025
(This article belongs to the Section Inorganic Crystalline Materials)
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Versions Notes

Abstract

The growing demand for safe and reliable weaponry has heightened performance requirements for explosives. Cocrystal systems, offering a balance between high energy density and safety, have become key targets in advanced energetic material research. However, the influence of molar ratios and crystal facets on thermal sensitivity, mechanical strength, and detonation properties remains underexplored. This study investigates cocrystals of hexanitrohexaazaisowurtzitane (CL-20) and 1,1-diamino-2,2-dinitroethylene (FOX-7) with molar ratios of 3:1, 5:1, and 8:1 on the (1 0 1) crystal facet, using the Forcite module in Materials Studio. Comparative analysis with (0 1 1) facet and pure explosives revealed that the 5:1 cocrystal achieved the highest cohesive energy density (0.773 kJ/cm3) and theoretical crystal density (1.953 g/cm3), driven by strong electrostatic and non-bonded interactions—indicating superior detonation performance. In contrast, the 3:1 cocrystal displayed optimal mechanical strength, with an elastic modulus of 8.562 GPa and shear modulus of 3.365 GPa, suitable for practical applications. The results suggest increasing CL-20 content enhances energy performance up to a point, beyond which structural loosening occurs (8:1 ratio) due to steric hindrance weakening van der Waals forces. This work clarifies how molar ratio regulates the influence between sensitivity, strength, and energy, providing guidance for designing application-specific high-energy cocrystals.

1. Introduction

In the development of high-energy, insensitive explosives, current research primarily focuses on two strategies: the design and synthesis of novel energetic molecules, and the optimization of existing explosive formulations. However, both molecular and experimental design for new explosives present significant challenges [1]. Consequently, researchers have turned to desensitization techniques such as nanostructuring [2,3,4], coating [5,6,7,8,9], blending, and particularly cocrystallization [10,11]. This method can improve deficiencies in individual components, achieving better sensitivity, thermal stability, detonation performance, and processability [12,13,14,15,16,17,18].
While research has largely centered on second-generation explosives such as HMX, the HMX/HNS system reported by Veerabhadragouda B. Patil et al. [19,20] indicates that even slight changes in the ratio can have a decisive impact on the mechanical sensitivity and thermal stability of the eutectic. These materials often fail to meet the performance demands of future military applications. Third-generation explosives, such as CL-20 (hexanitrohexaazaisowurtzitane), offer higher detonation performance. ε-CL-20, for instance, has a theoretical crystal density exceeding 2 g/cm3 and has attracted considerable attention due to its high energy and favorable oxygen balance. However, its high sensitivity limits its practical use [21,22,23,24].
To overcome this, insensitive materials are often introduced via cocrystallization. FOX-7 (1,1-diamino-2,2-dinitroethylene) is a promising insensitive energetic compound featuring a planar conjugated structure and strong intramolecular hydrogen bonding, which confer high density and thermal stability. Its energy output is comparable to RDX [25], and when cocrystallized with CL-20, it can meet both energetic and safety requirements. Given that both CL-20 and FOX-7 are composed of C, H, O, and N elements and contain nitro groups (–NO2), they are likely to form stable cocrystals via hydrogen bonding—offering a viable route toward high-energy, low-sensitivity materials.
Previous studies, such as the 2012 work by Onas Bolton et al., demonstrated that a 2:1 CL-20/HMX cocrystal reduced sensitivity relative to pure CL-20. Nonetheless, fundamental mechanisms behind CL-20 cocrystallization remain poorly understood. Molecular dynamics (MD) simulations offer insight into molecular-level interactions. For example, Liu et al. [26] used MD to show that the cohesive energy density of CL-20/TNT cocrystals far exceeded that of their physical mixtures. Wen et al. [27] simulated CL-20/TATB cocrystal formation, identifying the (1 0 –1) facet as energetically favorable. R. Wild et al. [28] compared detonation parameters across several insensitive explosives, affirming FOX-7’s high shock initiation pressure (8.24 GPa) and low sensitivity characteristics. Fu et al. [29] studied the thermal decomposition process of FOX-7. The decomposition may be composed of some simultaneous reactions, and the condensation reaction of FOX-7 may occur at the beginning of the reaction to create an equilibrium state of the condensation reaction products. As the reaction temperature continues to rise, the equilibrium state of the condensation product is destroyed, and FOX-7 molecules begin to decompose into small functional groups and some small molecular products. The most likely main decomposition pathway is shown in Figure 1 below.
Additionally, Wu et al. [30] modeled the crystallization of CL-20 and FOX-7 on various crystal planes, suggesting FOX-7 preferentially substitutes onto the (1 0 1) plane of CL-20. HANG et al. [31] examined cocrystals of differing molar ratios and facets but provided no mechanistic interpretation.
To investigate the intrinsic laws of crystallization of CL-20 and FOX-7, this study constructed co-crystalline explosive models composed of CL-20 and FOX-7 under three different molar ratios. Energy and geometry optimizations were performed to ensure thermodynamic stability, followed by MD simulations to assess structural equilibrium. The Forcite module was used to evaluate mechanical properties, while cohesive energy density and Kamlet–Jacobs equations were applied to assess thermal sensitivity and detonation performance, respectively.

2. Computational Methods

The relevant simulation calculations were completed using Materials Studio 2020 [32] software. In this paper, ε-CL-20 and β-FOX-7 were selected for research. Among the polymorphs of CL-20, the ε form is the most stable isomer at room temperature, with the highest crystal density (exceeding 2.0 g/cm3) and moderate sensitivity, and is the most widely used crystal form in practical applications. The β form of FOX-7 is the thermodynamically stable phase, and its planar conjugated structure and strong intramolecular hydrogen bond network endow it with excellent insensitivity performance.
The single crystal models of ε-CL-20 and β-FOX-7 were constructed through the CCDC database, as shown in Figure 2. According to the principle of co-crystal formation, hydrogen bonds are the most important interaction force in co-crystal systems. CL-20 contains polar NO2 groups, and FOX-7 contains NH2 groups, which can form N-O…H type hydrogen bonds. Considering the possible intermolecular hydrogen bonds between CL-20 and FOX-7 molecules, FOX-7 acts as the donor of hydrogen bonds and CL-20 as the acceptor in the CL-20/FOX-7 co-crystal, and the initial supramolecular structure was constructed. Relevant literature indicates [30] that CL-20 and FOX-7 are more likely to form co-crystals on the (1 0 1) crystal plane, and the model is more stable. Therefore, the (1 0 1) crystal plane of CL-20 was studied. Based on different molar ratios of CL-20/FOX-7, a total of three co-crystal models were established. Taking the molar ratio of CL-20 to FOX-7 as 3:1 as an example, the co-crystal model was established as follows: First, a single unit cell of ε-CL-20 was established; then, it was expanded to a 16-unit supercell model (4 × 2 × 2), containing 64 CL-20 molecules. Finally, 16 FOX-7 molecules were randomly replaced with an equal amount of CL-20 molecules on the (1 0 1) growth crystal plane. The initial density of all models was set to the theoretical predicted value of the co-crystal recorded in reference [31] (for example, the initial density of the 5:1 model was set to 1.95 g/cm3), and relaxation was carried out from this starting point. The relevant parameters of each co-crystal model are shown in Table 1.
Molecular dynamics simulations were conducted using the first-generation COMPASS force field (COMPASS Forcefield). The parameterization of this force field for nitramine compounds (such as CL-20) and nitroso compounds (such as FOX-7) has been extensively studied and validated [26,30]. The COMPASS force field was developed and parameterized by Sun [33] in 1998, and it can accurately describe the bonding and non-bonding interactions in organic molecules and their crystals. Both isomers have well-established parameters in the COMPASS force field, and the crystal structures match well with the experimental data, thus accurately reflecting the true characteristics of the co-crystal system. Compared to COMPASSII, it has higher reliability in predicting density, mechanical properties, thermodynamic properties, compatibility, and the formation ability/stability of co-crystals.
To construct a series of eutectic models with varying molar ratios (3:1, 5:1, 8:1) oriented along the (1 0 1) crystal plane, the eutectic growth behavior guided by this crystallographic orientation was systematically investigated. Initially, based on experimental crystallographic data, the unit cells of the two constituent materials were cleaved along the (1 0 1) plane to extract the characteristic molecular packing pattern on this facet. The resulting surfaces were then saturated with hydrogen atoms and charge-balanced to eliminate potential dangling bond effects and ensure system stability. Subsequently, the cleaved surface models were expanded into supercells according to the target molar ratios. Using the Build Layers module, initial eutectic structures with the desired stoichiometries were generated. To adequately sample the configuration space, five independent initial models were constructed for each molar ratio following this procedure. All models were built under three-dimensional periodic boundary conditions to ensure that key molecular interactions were preferentially aligned along the (1 0 1) crystallographic direction. During the optimization phase, each initial configuration underwent molecular dynamics annealing simulations followed by geometric energy minimization to remove unrealistic intermolecular contacts and stabilize the layered packing framework. The most representative optimized model for each molar ratio was selected based on two criteria: minimization of the total system energy, and convergence of the (1 0 1) plane structural parameters—such as interlayer spacing and molecular plane angles—toward experimentally observed values. This structured modeling approach ensured that the constructed models accurately captured the eutectic assembly mechanism along the specified crystal plane for subsequent mechanistic analysis.
The initial models were energy minimized using the Energy module under the Forcite module and geometrically optimized using the Geometry Optimization module. Finally, the Dynamics module was used for the molecular dynamics simulation of the co-crystal models. Andersen temperature control [34] was selected, with a temperature set at 298 K. The van der Waals and electrostatic interactions were calculated using the Atom based [35] and Ewald [36] methods, respectively. The cutoff value and buffer width for the Atom-based method were 15.5 Å and 2 Å, respectively. The precision of the Ewald method was set at 1.0 × 10−4 kcal/mol. An annealing cycle and ensemble equilibration were used to eliminate metastable and artifact structures. First, three heating and cooling cycles (rate of 5 K/ps) were performed under the NPT ensemble to eliminate initial artifacts. After annealing, the system was equilibrated for 200 ps under the NPT ensemble, and then switched to the NVT ensemble for 200 ps until the temperature fluctuation was less than 20 K and the energy fluctuation of the system was no more than 10%, indicating that the CL-20/FOX-7 co-crystal simulation system had reached equilibrium.
All initial configurations underwent the same annealing cycle and energy minimization procedure and were finally selected based on a comprehensive evaluation method of three criteria: (i) having the lowest time-averaged potential energy in the final NVT equilibrium stage; (ii) having a mass density value close to the experimental or literature data [30,31]; (iii) having reasonable crystallographic symmetry and periodicity in the final equilibrium structure to ensure structural stability. Using the above method, co-crystal models of CL-20/FOX-7 with molar ratios of 3:1, 5:1, and 8:1 were constructed, as shown in Figure 3.
To evaluate the energetic and mechanical behavior of CL-20, FOX-7, and their cocrystals, theoretical calculations were conducted. Thermal sensitivity was characterized via cohesive energy density, van der Waals, and electrostatic interactions. Mechanical properties including Young’s modulus, shear modulus, Cauchy pressure, and Poisson’s ratio were analyzed to assess processing suitability. Detonation performance was estimated using Kamlet–Jacobs equations based on the theoretical crystal densities, allowing comparison with pure FOX-7 to assess enhancements conferred by cocrystallization.

3. Results

3.1. Cohesive Energy Density Comparison

Cohesive energy density (CED) reflects the strength of intermolecular interactions and is primarily governed by van der Waals and electrostatic forces [37]. A higher CED indicates greater resistance to sublimation from the condensed phase to the gas phase, which generally corresponds to lower sensitivity and enhanced thermal stability.
As shown in Table 2, among the three CL-20/FOX-7 cocrystals, the 5:1 molar ratio system exhibits the highest CED (0.773 kJ·cm−3), with the strongest electrostatic interaction (0.432 kJ·cm−3) and relatively high van der Waals contribution (0.329 kJ·cm−3). This suggests that the 5:1 composition offers an optimal balance between interaction forces, indicating superior thermal stability and making it a promising candidate for high-energy applications.
However, the CED values of all three cocrystal systems are lower than that of pure FOX-7 (1.208 kJ·cm−3). This reduction may be attributed to the inability of the cocrystal structures to fully retain the strong intermolecular interactions intrinsic to pure FOX-7, resulting in a diminished overall cohesive force within the system.

3.2. Mechanical Properties

Mechanical performance is critical to the processing and application of energetic materials. Young’s modulus (E) characterizes resistance to elastic deformation, shear modulus (G) reflects resistance to shear deformation, and bulk modulus (K) indicates resistance to volumetric compression [38]. These parameters are interrelated through the elastic mechanics model by the following equations:
K = E 3 × 1 − 2 γ
G = E 2 × 1 + γ
Cauchy pressure (C12–C44) and Poisson’s ratio (γ) are commonly used to assess material ductility. The results for each model are listed in Table 3.
Analysis shows that the 3:1 CL-20/FOX-7 cocrystal exhibits the highest Young’s and shear moduli, indicating superior mechanical strength and potential suitability as a robust energetic matrix. The 5:1 cocrystal shows a relatively high Poisson’s ratio (0.324), which may affect its structural stability under dynamic loading—warranting further detonation performance simulations or shock experiments. In contrast, the 8:1 cocrystal demonstrates an overall decline in mechanical performance, suggesting the need for ratio optimization or incorporation of additional stabilizing components.

3.3. Detonation Performance

Detonation performance directly reflects the practical value of a cocrystal explosive and is closely related to its density and chemical composition. The Kamlet–Jacobs equations [39], a semi-empirical model widely used for CHNO-type explosives with loading densities above 1 g/cm3, provide an efficient and accurate method for estimating detonation velocity (vD) and pressure (p2). These equations are particularly advantageous for evaluating cocrystal explosives due to their high precision and engineering applicability. The equations are expressed as:
p 2 = 7.617 × 10 6 φ ρ 0 2
v D = 7060 φ 1 / 2 1 + 1.3 ρ 0
φ = N M Q
p 2 represents the Chapman–Jouguet (C–J) detonation pressure in pascals, the stable pressure at the end of the chemical reaction zone behind the detonation front (Pa), and v D denotes the C–J detonation velocity in meters per second, Velocity of stable propagation of detonation wave in explosive (m/s). The term ρ 0 is the loading density of the explosive (g/cm3). N is the number of moles of gaseous detonation products generated per gram of explosive (mol/g), M is the average molecular weight of these gaseous products (g/mol), and Q is the heat of detonation at constant pressure (J/g). The parameter φ , referred to as the characteristic value of the explosive, is defined as N M Q .
For cocrystal models, the optimized model densities were used in detonation calculations, while the parameters for pure CL-20 and FOX-7 were obtained from literature [23]. The theoretical detonation velocity and pressure values for each system are summarized in Table 4.
By comparing the densities of the three cocrystal explosives, it is evident that the density does not increase monotonically with higher CL-20 content. Specifically, the CL-20/FOX-7 (5:1) cocrystal exhibits the highest density at 1.953 g/cm3, exceeding that of both the 8:1 cocrystal (1.870 g/cm3) and the 3:1 cocrystal (1.951 g/cm3). Referring to the cohesive energy density data, this can be attributed to the saturation of non-bonded interactions between CL-20 and FOX-7 molecules as the FOX-7 content decreases. At a molar ratio of approximately 5:1, the system reaches a maximum in intermolecular interactions. Beyond this point, excess CL-20 molecules fail to form effective interactions, resulting in weakened intermolecular forces and expanded crystal volume—manifested as a decrease in density [1].
At 298 K, the 5:1 CL-20/FOX-7 cocrystal demonstrates superior detonation performance among the three ratios. Both the calculated detonation velocity and pressure surpass those of the FOX-7 single crystal. Although slightly lower than those of pure CL-20, the 5:1 cocrystal shows an 8.18% increase in detonation velocity and a 20.6% increase in detonation pressure compared to FOX-7, confirming its advantage as a high-energy, low-sensitivity explosive candidate.

3.4. Performance Comparison on Alternative Crystal Facets

To further investigate whether the intrinsic trends observed on the (1 0 1) facet also manifest on other crystal planes, a morphological analysis was conducted to identify alternative growth facets of CL-20. Based on the attachment energy method, which predicts growth rates by the relative ability of different crystal planes to attract molecules, the (0 1 1) facet was identified as another likely surface for cocrystal formation. Consequently, the (0 1 1) facet was selected for further modeling and performance evaluation using the same computational parameters as in previous sections. The resulting performance data are summarized in Table 5.
The results show that the same trend persists: the cocrystal density does not increase linearly with increasing CL-20 content. Instead, the density reaches its maximum at a 5:1 molar ratio. The density at 3:1 is comparable and also exceeds that of the 8:1 system, again highlighting the role of non-bonded interactions in the cocrystallization process. This suggests that high-density component content alone does not determine the final density of the cocrystal; rather, interaction saturation between the components must be considered.
Moreover, both the densities and cohesive energy parameters of cocrystals formed on the (0 1 1) facet are lower than those formed on the (1 0 1) facet at the same molar ratios. This indicates that the (1 0 1) facet provides a more favorable structural arrangement for CL-20 and FOX-7 interactions, resulting in stronger intermolecular forces and more stable cocrystal formation.

4. Discussion

The CED of the CL-20/FOX-7 cocrystal systems (ranging from 0.671 to 0.773 kJ·cm−3) is notably higher than that of pure CL-20 (0.654 kJ·cm−3), indicating that the cocrystallization process enhances intermolecular interactions. This enhancement is closely related to the high polarity of FOX-7, where strong dipole interactions between amino (–NH2) and nitro (–NO2) groups contribute to its significant electrostatic component (accounting for 54.4% of its CED). However, in the cocrystal, these interactions are partially restricted by the steric hindrance of CL-20’s cage-like structure. Notably, at a 5:1 molar ratio, the electrostatic (0.432 kJ·cm−3) and van der Waals (0.329 kJ·cm−3) interactions in the cocrystal reach an optimal balance, yielding the highest CED (0.773 kJ·cm−3) among all cocrystal systems—although still only 64% of pure FOX-7. This suggests that while the introduction of CL-20 compromises cohesive energy to some extent, it may relieve lattice stress in FOX-7 through molecular reconfiguration, thereby enhancing thermodynamic stability (e.g., suppression of phase transitions). From Table 2, the mechanical performance reflects a synergy between energy density and safety. The 3:1 cocrystal shows a Young’s modulus of 8.562 GPa and shear modulus of 3.365 GPa—approximately 50% of pure CL-20 (16.5 GPa and 5.5 GPa, respectively), but significantly higher than FOX-7 (5.616 GPa and 2.134 GPa). Combined with a Cauchy pressure of 0.6185 GPa and Poisson’s ratio γ = 0.272, the 3:1 cocrystal exhibits moderate ductility, potentially accommodating plastic deformation under dynamic loading. However, the higher Poisson’s ratio of the 5:1 cocrystal (γ = 0.324) may indicate increased risk of localized stress concentrations, warranting further validation through impact or shear failure testing. The mechanical properties of the 8:1 cocrystal (E = 6.14 GPa, G = 2.402 GPa) are comparable to those of pure FOX-7, suggesting that excessive CL-20 results in a loosened cocrystal structure—corroborated by the CED drop to 0.671 kJ·cm−3 (Table 1), which reflects the negative impact of non-bonded interaction saturation. As shown in Table 3, the 5:1 cocrystal achieves the best detonation performance, with a detonation velocity of 9437.7 m/s and pressure of 41.6 GPa—97.1% and 91.8% of pure CL-20 values (9717 m/s and 45.3 GPa), respectively. This aligns with its peak CED and density (1.953 g/cm3), indicating an optimal synergy between CL-20’s high energy output and FOX-7’s insensitivity. The fact that the 5:1 cocrystal density exceeds that of the 8:1 system (1.877 g/cm3) further supports the role of non-bonded interaction saturation in regulating molecular packing efficiency [19]. Additionally, on the (0 1 1) facet, the cocrystal density (1.867 g/cm3) and CED (0.654 kJ·cm−3) are lower than those on the (1 0 1) facet (1.953 g/cm3 and 0.773 kJ·cm−3), suggesting that the (1 0 1) facet of CL-20, due to its more exposed nitro group sites, facilitates stronger hydrogen bonding with FOX-7, leading to more ordered molecular alignment. In the CL-20/FOX-7 cocrystal system, the 5:1 molar ratio achieves an optimal synergy between molecular ordering and energy–insensitivity balance through saturation of non-bonded interactions (electrostatic and van der Waals forces). The peak values of cohesive energy density (0.773 kJ·cm−3) and crystal density (1.953 g/cm3) suggest that the cage-like structure of CL-20, via hydrogen bonding networks anchored at nitro exposure sites, reconstructs the lattice stress distribution of FOX-7—thereby suppressing phase transitions while enhancing detonation performance (velocity and pressure reaching 97% and 92% of pure CL-20, respectively). Additionally, the balanced mechanical profile (E = 7.405 GPa, γ = 0.324) reflects a coupled mechanism between structural stability under dynamic loading and efficient energy release. Under this composition, the choice of crystal facet further amplifies molecular synergism, offering a generalizable strategy for designing high-energy, insensitive explosives based on the concept of “non-bonded interaction saturation coupled with facet-oriented regulation.” The results of this study are different from the conclusions of molecular dynamics simulation of Hang [28], as shown in Figure 4. Based on the random substitution model of polycrystal faces, Hang [28] pointed out that CL-20/FOX-7 eutectic has the highest binding energy and comprehensive mechanical properties at 1:1 molar ratio, so it is the easiest to form and the most stable. However, in this paper, the cohesive energy density (CED), detonation properties and mechanical properties were systematically analyzed by focusing on the (101) crystal plane, and the eutectic system showed a clear division of labor characteristics: 5:1 molar ratio in the detonation properties (density: 1.953 G/cm 3; Detonation velocity: 9437.7 m/s) and thermal stability (CED: 0.773 kJ/cm 3), while the 3:1 ratio has better mechanical properties (elastic modulus: 8.562 GPa). This divergence is due to different research paradigms: Hang focuses on the “formation ability” of cocrystals, while this study further reveals that the “practical performance after formation” of cocrystals is regulated by the saturation effect of non-bonding forces, that is, electrostatic and Van der Waals forces reach a synergistic optimum near 5:1, while excessive CL-20 leads to structural loosening due to steric hindrance. Therefore, this study does not deny the formation advantage of 1:1 ratio, but it is clear that it is not the optimal solution of performance, and then a new strategy of “on-demand” eutectic design is proposed: 5:1 is preferred for detonation, and 3:1 is preferred for mechanical properties, which provides a more instructive theoretical scheme for the design of high-energy materials.

5. Conclusions

In this study, molecular dynamics simulations were employed to evaluate the cohesive energy densities of CL-20/FOX-7 cocrystal explosives with molar ratios of 3:1, 5:1, and 8:1 on the (1 0 1) and (0 1 1) crystal facets. Mechanical properties were also estimated for each composition, and detonation velocity and pressure were calculated based on simulation data using the Kamlet–Jacobs method.
The results demonstrate that on the (1 0 1) facet, the 5:1 cocrystal exhibits the highest density and best thermodynamic stability, making it a promising candidate for high-energy, low-sensitivity explosive applications. Non-bonded interactions were found to play a critical role in the structural stability of the cocrystal systems. Density analyses across both crystal facets indicate that increasing the CL-20 content does not lead to a linear density increase; instead, a local maximum appears near the 5:1 molar ratio.
Meanwhile, the 3:1 cocrystal exhibits superior mechanical strength, suggesting better suitability for processing and practical application. These findings imply that cocrystals with molar ratios between 3:1 and 5:1 may offer an optimal balance among thermal sensitivity, mechanical robustness, and detonation performance—pointing to a promising compositional window for the design of advanced energetic cocrystals.

Author Contributions

Conceptualization, R.Z., Y.L. and S.Z.; Methodology, R.Z., S.L. and Y.L.; Software, R.Z. and K.Q.; Validation, R.Z., Y.L. and K.Q.; Formal analysis, R.Z. and S.Z.; Investigation, R.Z., S.L. and S.Z.; Resources, Y.W., T.W., S.L. and X.L.; Data curation, Y.W. and X.L.; Writing—original draft, R.Z. and K.Q.; Writing—review & editing, Y.W. and T.W.; Visualization, R.Z., S.L. and X.L.; Supervision, T.W.; Project administration, T.W.; Funding acquisition, T.W. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Natural Science Basic Research Program of Shaanxi (Program No.2024JC-ZDXM-01).

Data Availability Statement

The original data presented in the study are openly available in CCDC at [DOI: 10.5517/cc8flqz].

Conflicts of Interest

The authors declare no conflict of interest.

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Crystals 15 00912 g001
Figure 1. Thermal decomposition process of FOX-7 [28].
Figure 1. Thermal decomposition process of FOX-7 [28].
Crystals 15 00912 g001
Crystals 15 00912 g002
Figure 2. Two single-unit cell models (a) ε-CL-20 (b) β-FOX-7.
Figure 2. Two single-unit cell models (a) ε-CL-20 (b) β-FOX-7.
Crystals 15 00912 g002
Crystals 15 00912 g003
Figure 3. Eutectic models of CL-20/FOX-7 with different molar ratios (a) 3:1 (b) 5:1 (c) 8:1.
Figure 3. Eutectic models of CL-20/FOX-7 with different molar ratios (a) 3:1 (b) 5:1 (c) 8:1.
Crystals 15 00912 g003
Crystals 15 00912 g004
Figure 4. Eutectic density of CL-20/FOX-7 at different molar ratios.
Figure 4. Eutectic density of CL-20/FOX-7 at different molar ratios.
Crystals 15 00912 g004
Table 1. The correlated parameters of CL-20/FOX-7 cocrystal models.
Table 1. The correlated parameters of CL-20/FOX-7 cocrystal models.
Molar RatioMass Percent (%)Supercell ModelTotal Number of Atoms
(CL-20:FOX-7)
1:001003 × 3 × 22592
8:01723 × 3 × 22416
5:01483 × 2 × 21552
3:01644 × 2 × 21952
0:0104 × 3 × 21344
Table 2. Cohesive energy density and its components between the components of CL-20/FOX-7 eutectic and single crystal.
Table 2. Cohesive energy density and its components between the components of CL-20/FOX-7 eutectic and single crystal.
CED/kJ·cm−3van der Waals /kJ·cm−3Electrostatic/kJ·cm−3
CL-200.6540.320.323
FOX-71.2080.5370.657
CL-20/FOX-7 (3:1)0.7410.340.389
CL-20/FOX-7 (5:1)0.7730.3290.432
CL-20/FOX-7 (8:1)0.6710.3060.354
Table 3. Mechanical performance parameters of CL-20, FOX-7 and their eutectic explosives.
Table 3. Mechanical performance parameters of CL-20, FOX-7 and their eutectic explosives.
E/GPaK/GPaG/GPaC12–C44/GPaγ
CL-2016.510.55.51.20.25
FOX-75.6165.0822.1342.30820.31
CL-20/FOX-7 (3:1)8.5626.2643.3650.61850.272
CL-20/FOX-7 (5:1)7.4055.0242.9521.63640.324
CL-20/FOX-7 (8:1)6.144.6122.4020.16040.206
Table 4. Detonation performance parameters of CL-20, FOX-7 and their eutectic explosives.
Table 4. Detonation performance parameters of CL-20, FOX-7 and their eutectic explosives.
Density/g·cm−3CL-20/%Detonation/m·s−1Burst Pressure/GPa
CL-20 2.04100971745.3
FOX-7 1.8650872434.5
CL-20/FOX-7 (3:1)1.95189.759386.441.1
CL-20/FOX-7 (5:1)1.95392.19437.741.6
CL-20/FOX-7 (8:1)1.87795.349208.438.7
Table 5. (0 1 1) crystal plane parameter calculation results.
Table 5. (0 1 1) crystal plane parameter calculation results.
Density/g·cm−3CED/kJ·cm−3van der WaalsElectrostatic
CL-20 2.040.6540.320.323
FOX-7 1.8651.2080.5370.657
CL-20/FOX-7 (3:1) 1.8320.6940.2930.391
CL-20/FOX-7 (5:1) 1.8670.6540.2930.391
CL-20/FOX-7 (8:1) 1.770.6530.2740.37
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Zheng, R.; Wang, Y.; Wang, T.; Li, S.; Luo, Y.; Liu, X.; Quan, K.; Zhang, S. Molecular Dynamics Study on the Molar Ratio-Dependent Interaction Regulation Mechanisms in CL-20/FOX-7 Energetic Cocrystal Explosives. Crystals 2025, 15, 912. https://doi.org/10.3390/cryst15110912

AMA Style

Zheng R, Wang Y, Wang T, Li S, Luo Y, Liu X, Quan K, Zhang S. Molecular Dynamics Study on the Molar Ratio-Dependent Interaction Regulation Mechanisms in CL-20/FOX-7 Energetic Cocrystal Explosives. Crystals. 2025; 15(11):912. https://doi.org/10.3390/cryst15110912

Chicago/Turabian Style

Zheng, Ruikang, Yuling Wang, Tao Wang, Shuchang Li, Yibo Luo, Xingyu Liu, Kaizeng Quan, and Shusheng Zhang. 2025. "Molecular Dynamics Study on the Molar Ratio-Dependent Interaction Regulation Mechanisms in CL-20/FOX-7 Energetic Cocrystal Explosives" Crystals 15, no. 11: 912. https://doi.org/10.3390/cryst15110912

APA Style

Zheng, R., Wang, Y., Wang, T., Li, S., Luo, Y., Liu, X., Quan, K., & Zhang, S. (2025). Molecular Dynamics Study on the Molar Ratio-Dependent Interaction Regulation Mechanisms in CL-20/FOX-7 Energetic Cocrystal Explosives. Crystals, 15(11), 912. https://doi.org/10.3390/cryst15110912

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