Canonical Monte Carlo Simulations Research Articles

Interpenetrated In(III)-MOF with Multiple Recognition Sites for Single-Step Ethylene Purification.

An interpenetrated indium(III) metal-organic framework (MOF), NTUniv-73, with a rarely reported tetrameric indium cluster is developed for streamlining ethylene purification from C2 gases. At 298 K, the adsorption capacities exhibited a complete reversal sequence of C2H6 > C2H2 > C2H4. Grand canonical Monte Carlo simulation indicated that the corners in a octahedral cage facilitated the C2H2/C2H4 separation, while the pocket-like aperture situated between adjacent octahedral cages allows for full contact of C2H6. Breakthrough experiments illustrated that NTUniv-73 could yield pure C2H4 in a single step with a productivity of 0.42 mmol g-1.

Electrostatically driven kinetic inverse CO2/C2H2 separation in LTA-type zeolites

The identical molecular size and similar physical properties of carbon dioxide (CO2) and acetylene (C2H2) make their adsorptive separation extremely challenging to achieve with most adsorbents. Reports on the separation of CO2 and C2H2 mixtures by zeolites are even rarer with the mechanism of adsorptive separation requiring further exploration. In this paper, we report that ion modulation of zeolite 5A promotes the difference in kinetic diffusion of CO2 and C2H2, realizing the inverse separation of zeolite from selective adsorption of C2H2 to selective adsorption of CO2. Creating a compact pore space restricting the orientation of gas molecules enables charge recognition. The positive electrostatic potential at the pore openings was utilized to hinder the diffusion of C2H2 between the cages while ensuring the transfer of CO2, increasing their diffusion differences in pore channels and leading to the CO2/C2H2 kinetic selectivity of 31.97. Grand canonical Monte Carlo (GCMC) simulation demonstrates that the CO2 distribution in K-5A-β is significantly higher than that of C2H2. Dynamic breakthrough experiments verify the excellent performance of material in practical CO2/C2H2 separation, for CO2/C2H2 (50/50 and 1/99, V/V) mixtures can be separated in one step, thus directly generating high purity C2H2 (> 99.95%), which provides a promising thought for the zeolite-based separation of CO2 and C2H2.

Direct Ethylene Purification from a Four-Component Gas Mixture by a Microporous MOF with Aromatic Pore Surface and Carboxylates.

The single-step purification of ethylene (C2H4) from a mixture of carbon dioxide (CO2), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6) was achieved through MOF Compound-1, where the aromatic pore surface and carboxylates selectively recognized C2H6 and CO2, respectively, resulting in a reversal of the adsorption orders for both gases (C2H6 > C2H4 and CO2 > C2H4). Breakthrough testing verified that the C2H4 purification ability could be enhanced 2.6 times after adding impure CO2. Grand Canonical Monte Carlo (GCMC) simulations demonstrate that there are interactions between CO2 and C2H6 molecules as well as between CO2 molecules themselves. These interactions contribute to the enhancement of the C2H4 purification ability upon the addition of CO2 and the increased adsorption of CO2.

Improving Stability, Crystallinity, and Photo‐Responsiveness of Supramolecular Frameworks by Surface Polymerization

AbstractMetal–organic cage‐based photo‐responsive supramolecular frameworks (PSMFs) with permanent porosity have gained attention for their modular properties, controllable functionality, and light‐induced reversible responsiveness. However, their high porosity and photo‐responsive efficiency are often compromised due to poor structural stability upon solvent removal, limiting their potential applications. Here, a solution to overcome this challenge by employing a surface polymerization strategy using isophorone diisocyanate (IDI) to stabilize PSMF (PCC‐20t) is presented. This approach results in the composite of PCC‐20t@PolyIDI, which preserves crystallinity and permanent high‐porosity while avoiding structural collapse commonly observed in highly porous supramolecular frameworks. Moreover, compared to activated PCC‐20t, PCC‐20t@PolyIDI exhibits an 18.6‐fold increase in specific surface area. Remarkably, the structural variability of PCC‐20t@PolyIDI can be observed in the photo‐regulation behavior of CO2 capacity under the irradiation of vis‐ and UV‐light, showing a 27.9% change in adsorption amount for CO2 which is significantly higher than that of the activated PCC‐20t with 7.0% for CO2. Grand Canonical Monte Carlo simulations demonstrate the light‐regulated adsorption performance is attributed to the configuration transformation of azobenzene from trans‐ to buckling state. The findings may pave the way for stabilizing high‐porosity materials to simultaneously meet demands for high‐porosity and photo‐responsive efficiency.

Exploring Methane Storage Capacities of M2(BDC)2(DABCO) Sorbents: A Multiscale Computational Study

A promising solution for efficient methane (CH4) storage and transport is a metal–organic framework (MOF)-based sorbent. Hence, searching for potential MOFs like M2(BDC)2(DABCO) to enhance the CH4 storage capacity in both gravimetric and volumetric uptakes is essential. Herein, we systematically elucidate the adsorption of CH4 in M2(BDC)2(DABCO) or M(DABCO) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn) MOFs using multiscale simulations that combined grand canonical Monte Carlo simulation with van der Waals density functional (vdW-DF) calculation. We find that, in the M(DABCO) series, Mg(DABCO) has the highest total CH4 adsorption capacities, with mtot= 231.39 mg/g at 298 K, for gravimetric uptake, and Vtot= 231.43 cc(STP)/cc, for volumetric uptake. The effects of temperature, pressure, and metal substitution on enhancing CH4 storage are evaluated, and we predict that the volumetric CH4 storage capacity on M(DABCO) could meet the DOE target at temperatures of ca. 238 K–268 K and pressures of 35–100 bar. The interactions between CH4 and M(DABCO) are dominated by the vdW interactions, as shown by the vdW-DF calculations. The Mg, Mn, Fe, Co, and Ni substitutions in M(DABCO) result in a stronger interaction and thus, a higher CH4 storage capacity, at higher pressures for Mg, Mn, Ni, and Co and at lower pressures for Fe. This work may provide guidance for the rational design of CH4 storage in M2(BDC)2(DABCO) MOFs.

Data-driven discovery of novel metal organic frameworks with superior ammonia adsorption capacity

Ammonia (NH3) has been a subject of great interest due to its important roles in diverse technological applications. However, high toxicity and corrosiveness of NH3 has made it an important task to develop an efficient carrier to safely capture NH3 with high capacity. Here, we employ a machine learning (ML) model to discover high-performance metal organic frameworks (MOFs) that will work as efficient NH3 carriers. By constructing databases at two distinct conditions, adsorption and desorption, through Grand Canonical Monte Carlo (GCMC) simulations to train ML models, we identify eight novel MOFs as potentially efficient NH3 carriers through screening the large-scale MOF databases with the trained models and GCMC verification. The identified MOFs exhibit the average NH3 working capacity exceeding 1100 mg/g, and subsequent molecular dynamics simulations demonstrate mechanical stability of the predicted MOFs. Moreover, analyses of the diffusion mechanism within the proposed MOFs underscore the strong dependence of NH₃ gas diffusivity on the structural details of the materials.

Adsorption properties of n-octane/1-octene binary mixtures in the zeolitic imidazolate frameworks, ZIF-8 and ZIF-67: Combined experimental and molecular simulation study

1-Octene, a linear α-olefin, can be used as a comonomer for producing plastics, oils, waxes, and surfactants. High-purity 1-octene can be obtained by removing paraffin byproducts using energy-intensive distillation. Adsorptive separation using porous material–based adsorbents is a promising alternative to distillation. Most reported adsorbents are zeolites, which preferentially adsorb 1-octene rather than n-octane owing to their polar framework. However, the existing studies are insufficient for investigating apolar adsorbents that adsorb more amounts of n-octane than 1-octene. Herein, the adsorption properties of the apolar adsorbents, zeolitic imidazolate frameworks-8 (ZIF-8) and ZIF-67, obtained from a n-octane/1-octene liquid binary mixture were systematically investigated by conducting batch adsorption experiments for the n-octane volume fraction of 10 %–90 %. Results show that ZIF-8 and ZIF-67 are promising adsorbents for the selective adsorption of n-octane owing to the preferential adsorption of n-octane in the micropores of the ZIFs at the high concentration of n-octane. Configurational-bias grand canonical Monte Carlo simulations confirm that the host–adsorbate energy between ZIF-8 and n-octane is higher than that between ZIF-8 and 1-octene, whereas the host–adsorbate energy between ZIF-67 and n-octane is similar to that between ZIF-67 and 1-octene.

Insight on molecular interactions in shrinkage of Na-montmorillonite clay by molecular dynamics simulation

Expansive soils are known to be hazardous materials for infrastructure due to their high shrinking or swelling potential. Understanding the shrinking factors of expansive soils such as montmorillonite (MMT) is essential for predicting their mechanical properties. The interactions between the components of Na-MMT clays, e.g., MMT layer–layer (LL), layer–cation (LC), layer–water (LW) and water–cation (WC), are responsible for its shrinking behavior. In this study, molecular dynamics simulation and grand canonical Monte Carlo simulations are used to investigate the interaction energy evolution in the layered structure of Na-MMT for the shrinkage mechanisms analysis of clay. The results of simulation indicate that the magnitude of the interaction energy contributed by the interlayer cations dehydration is the driving force of the interlayer shrinkage. Furthermore, in the hydrated state, with one water layer, two water layers and three water layers, the attractive interactions between WC and LW, maintain the stability of the clay layers. However, at the dry state, the interaction energy between layers and cations appears to be the most essential component in holding the stacked layers together, which provides structural stability to the clay sheets. Finally, the study reveals that intermolecular interactions contribute to the mechanical properties of clays such as cohesive and elastic properties.

Sequence dependence of critical properties for two-letter chains.

Histogram-reweighting grand canonical Monte Carlo simulations are used to obtain the critical properties of lattice chains composed of solvophilic and solvophobic monomers. The model is a modification of one proposed by Larson et al. [J. Chem. Phys. 83, 2411 (1985)], lowering the "contrast" between beads of different types to prevent aggregation into finite-size micelles that would mask true phase separation between bulk high- and low-density phases. Oligomeric chains of lengths between 5 and 24 beads are studied. Mixed-field finite-size scaling methods are used to obtain the critical properties with typical relative accuracies of better than 10-4 for the critical temperature and 10-3 for the critical volume fraction. Diblock chains are found to have lower critical temperatures and volume fractions relative to the corresponding homopolymers. The addition of solvophilic blocks of increasing length to a fixed-length solvophobic segment results in a decrease of both the critical temperature and the critical volume fraction, with an eventual slow asymptotic approach to the long-chain limiting behavior. Moving a single solvophobic or solvophilic bead along a chain leads to a minimum or maximum in the critical temperature, with no change in the critical volume fraction. Chains of identical length and composition have a significant spread in their critical properties, depending on their precise sequence. The present study has implications for understanding biomolecular phase separation and for developing design rules for synthetic polymers with specific phase separation properties. It also provides data potentially useful for the further development of theoretical models for polymer and surfactant phase behavior.

Microwave-synthesized heteroaromatic porous organic polymers for CO2 capture and hydrogen storage

In this paper, three porous organic polymers (POPs) were synthesized by microwave-assisted Friedel-Crafts polymerization reaction of 1,3,5-tris(2-thienyl)benzene (TTB) with furan (HAF), thiophene (HAT), and pyrrole (HAP) in the presence of dimethoxymethane using anhydrous iron (III) chloride as a catalyst. The polymers displayed inherent porosity, with BET surface areas ranging from 528 to 634 m2/g. These polymers exhibited high CO2 adsorption capacity, with values of 2.61, 2.17, and 2.37 mmol/g at 273 K and 1 atm, as well as strong affinity, with Qst values of 43–48 kJ/mol. The polymers showed hydrogen storage of 3.3–5.3 mmol/g (0.66–1.06 wt%) at 77 K, and 1 atm. The polymers showed Initial slope selectivity for CO2/N2: 34–61 at 273 K and 1 atm, and 23–57 at 298 K and 1 atm. Whereas, the polymers showed initial slope selectivity for CO2/CH4: 5–9 at 273 K and 4–7 at 298 K and 1 atm. Besides, the HAP at 273 K and HAF at 298 K showed highest IAST selectivity values of 231.18 and 257.49, respectively. Grand Canonical Monte Carlo (GCMC) simulations revealed that the polymers exhibit matching electronic properties with CO2 molecules and achieve excellent selectivity in accordance with the hard-soft acid-base (HSAB) theory. These findings demonstrate the potential of these polymers for CO2 capture and clean energy applications.

Computational design of novel highly connected COFs for CH4/H2 adsorption and separation

Ten new highly connected cubic boronitrate (-B4N4O12-) base covalent organic frameworks (BN-COFs) were designed in the lta and aco topologies. These structures were optimized and characterized computationally using density functional theory (DFT) and molecular mechanics methods. The structural characterization reflects that these BN-COFs possess the appropriate structural parameters for CH4/H2 adsorption and separation, such as low density (0.52–1.28 g·cm−3), high pore porosity (22 %-72 %), appropriate pore limiting diameter (PLD, 2.45–6.71 Å) and the largest cavity diameter (LCD, 3.21–19.96 Å), large pore volume (0.15–1.37 cm3·g−1) and accessible surface area (332–3974 cm2·g−1). Grand canonical Monte Carlo (GCMC) simulations were conducted to investigated the adsorption and separation properties of CH4 and H2 in ten BN-COFs. The results indicate that the uptake capacity of methane and hydrogen in BN-COF-5, −9 and −10 has exceeded the targets set by the U.S. Department of Energy (DOE). Furthermore, the CH4/H2 selectivity of ten BN-COFs is comparable to that of typical porous materials. The outstanding CH4/H2 adsorption and separation properties of these BN-COFs can provide some references and inspirations for researchers to develop high-performance porous adsorbents in experimental studies.

Molecular simulation of different VOCs adsorption on nitrogen-doped biochar

Nitrogen-doped biochar has potential application in the removal of volatile organic compounds (VOCs) from coal-fired flue gas. To explore the adsorption characteristics of different VOCs on nitrogen-doped biochar by molecular simulation, in this study, six typical aromatic VOCs (benzene, toluene, phenol, naphthalene, p-xylene, and chlorobenzene), and an amorphous carbon model with nitrogen/oxygen groups were selected and constructed. Grand Canonical Monte Carlo (GCMC) simulations were performed to evaluate the adsorption capacities of VOCs on nitrogen-doped biochar. The results showed that the optimized carbon model was in good agreement with the pore structure parameters of nitrogen-doped biochar, and the agreement of toluene adsorption capacities was more than 80 % at room temperature. The adsorption capacity of nitrogen-doped biochar for different VOCs was 184 − 317 mg/g with the order of phenol > naphthalene > p-xylene > toluene ≈ benzene ≈ chlorobenzene (single-component adsorption). Among them, the phenol molecule is more easily adsorbed due to its strong polarity, resulting in stronger electrostatic interaction with the adsorbent. The decrease rate of benzene adsorption capacity is the lowest with increasing adsorption temperature because of its low molecular weight. As gas concentration increases, van der Waals interactions between molecules and between molecules and porous carbon also increase, leading to an increase in VOCs adsorption capacity. Nitrogen-doped biochar not only has the highest VOCs/N2 selective adsorption coefficient for phenol (up to 36) but also has the highest adsorption capacity of 63 mg/g when 6 kinds of VOCs are multi-component adsorption at 25 °C. This study can provide references for the practical application of adsorption method in the removal of VOCs from coal-fired flue gas.

Reaching Quantum Accuracy in Predicting Adsorption Properties for Ethane/Ethene in Zeolitic Imidazolate Framework-8 at Low Pressure Regime.

Nanoporous materials in the form of metal-organic frameworks such as zeolitic imidazolate framework-8 (ZIF-8) are promising membrane materials for the separation of hydrocarbon mixtures. To compute the adsorption isotherms in such adsorbents, grand canonical Monte Carlo simulations have proven to be very useful. The quality of these isotherms depends on the accuracy of adsorbate-adsorbent interactions, which are mostly described using force fields owing to their low computational cost. However, force field predictions of adsorption uptake often show discrepancies from experiments at low pressures, providing the need for methods that are more accurate. Hence, in this work, we propose and validate two novel methodologies for the ZIF-8/ethane and ethene systems; a benchmarking methodology to evaluate the performance of any given force field in describing adsorption in the low-pressure regime and a refinement procedure to rescale the parameters of a force field to better describe the host-guest interactions and provide for simulation isotherms with close agreement to experimental isotherms. Both methodologies were developed based on a reference Henry coefficient, computed with the PBE-MBD functional using the importance sampling technique. The force field rankings predicted by the benchmarking methodology involve the comparison of force field derived Henry coefficients with the reference Henry coefficients and ranking the force fields based on the disparities between these Henry coefficients. The ranking from this methodology matches the rankings made based on uptake disparities by comparing force field derived simulation isotherms to experimental isotherms in the low-pressure regime. The force field rescaling methodology was proven to refine even the worst performing force field in UFF/TraPPE. The uptake disparities of UFF/TraPPE improved from 197% and 194% to 11% and 21% for ethane and ethene, respectively. The proposed methodology is applicable to predict adsorption across nanoporous materials and allows for rescaled force fields to reach quantum accuracy without the need for experimental input.

Effect of the Number of Methyl Groups in DMOF on N2O Adsorption and N2O/N2 Separation.

Nitrous oxide (N2O), as the third largest greenhouse gas in the world, also has great applications in industry, so the purification of N2O from N2 in industrial tail gas is a crucial process for achieving environmental protection and giving full play to its economic value. Based on the polarity difference of N2O and N2, N2O adsorption was researched on DMOF series materials with different polarities and methyl numbers of the ligand. N2O adsorption at 0.1 bar is enhanced, attributed to an increase of the methyl group densities at the benzenedicarboxylate linker. Grand canonical Monte Carlo simulations demonstrate the key role of methyl groups within the pore surface in the preferential N2O affinity. Methyl groups preferentially bind to N2O and thus enhanced low (partial) pressure N2O adsorption and N2O/N2 separation. The result shows that DMOF-TM has the highest N2O adsorption capacity (19.6 cm3/g) and N2O/N2 selectivity (23.2) at 0.1 bar. Breakthrough experiments show that, with an increase of the methyl number, the coadsorption time and retention time also increase, and DMOF-TM has the best N2O/N2 separation performance.

PACMAN: A Robust Partial Atomic Charge Predicter for Nanoporous Materials Based on Crystal Graph Convolution Networks.

We report a fast and easy method (PACMAN) to assign partial atomic charges on metal-organic framework (MOF) and covalent-organic framework (COF) crystal structures based on graph convolution networks (GCNs) trained on >1.8 million high-fidelity partial atomic charge data obtained from the Quantum Metal-Organic Framework (QMOF) database. The developed model shows outstanding performance, achieving a mean absolute error (MAE) of 0.0055 e (test set performance) while maintaining consistency with DDEC6, Bader, and CM5 charges across diverse chemistry and topologies of MOFs and COFs. We find that the new method accurately assigns partial atomic charges for ion-containing nanoporous materials, which has not been possible in previous machine learning (ML) models. Grand canonical Monte Carlo (GCMC) simulation results for CO2 and N2 uptakes and the Widom particle insertion calculation for Henry's law constant of water results based on PACMAN and the original DDEC6 charges show excellent agreements compared to other ML models reported in the literature. The runtime analysis of the new method demonstrates that the partial atomic charges of MOF and COF structures with up to 500 atoms can be obtained in less than 10 s. An easy-to-use web interface has been developed to facilitate the adoption of the developed model.

Selective adsorption of coalbed methane on multilayer defective graphene nanostructures and their Mn-modified nanostructures: A DFT study

Coalbed methane (CBM) is an unconventional natural gas with CH4 as the main component. It is found in coal seams and surrounding rocks. The development and exploitation of CBM is a promising approach to ensure the safety of coal mine production, reduce greenhouse effects, and increase clean energy resources. Based on the first-principles calculations in conjunction with a grand canonical Monte Carlo (GCMC) simulation, this paper aims to examine the effects of interlayer spacing and Mn modification on CBM and CO2 adsorption. We assess the CH4 storage performance in multilayered defective graphene nanostructures (MDGNs). Using density functional theory in conjunction with the Grimm correction method (DFT-D approach), both the adsorption energy and charge distribution between CBM components and extended line defects (ELD) are appropriately evaluated in the presence or lack of Mn modification (Mn-ELD). The GCMC simulation is implemented to investigate CH4 adsorption isotherms of MDGN and Mn-MDGN configurations at 298.15 K. The selective adsorption capabilities of MDGNs and Mn-MDGNs for CO2, N2, and CH4 are also systematically analyzed. The obtained results reveal that an Mn-MDGN configuration with an interlayer spacing of dGL=1.02 nm is effective in sequestering CO2 from CBM. In contrast, MDGN configurations with interlayer spacings of dGL=0.68 and 1.02 nm are more effective for the storage of purified CBM. In continuing, the CH4 purification mechanism in Mn-MDGNs and the CH4 storage mechanism in MDGNs are also methodically explored at the molecular level. The research work reported here can serve as a crucial guide for the future development and utilization of CBM.

Molecular engineering of a MOF with an ionic liquid sheath for direct air separation at ambient conditions

Combining ionic liquids (ILs) with metal–organic frameworks (MOFs) offers broad prospects for gas separation applications. However, identifying the best IL-MOF pair for a target gas separation solely based on experimental techniques is impractical. Herein, the promising IL and MOF combination was selected among 35,672 distinct ILs and 5,629 different MOFs by fusing computational methods at different molecular scales, density functional theory, conductor-like screening model for real solvents calculations, and grand canonical Monte Carlo simulations to engineer a MOF with an IL sheath (MOFILS) for direct air separation. The new MOFILS composed of [P6,6,6,14][DCA] and PCN-250(Fe) designed at the atomic level was then experimentally synthesized after fine-tuning the MOF to achieve high-performance air separation. An exceptionally high ideal O2/N2 selectivity of 26 was reached at 1 bar and 25 °C, boosting the benchmark value by four-times. The results of equilibrium and dynamic gas adsorption measurements further indicated a remarkably high selectivity of 382 for the separation of O2/N2:21/79 mixture, demonstrating the broad potential of the MOFILS designed in this work for direct air separation.

Spatial distribution of reduced density of hard spheres near a hard-sphere dimer: Results from three-dimensional Ornstein–Zernike equations coupled with several different closures and from grand canonical Monte Carlo simulation

We calculated the spatial distribution function, which is the one-body reduced density distribution of solvent particles around a nonspherical solute, using the three-dimensional Ornstein–Zernike equations coupled with closures. The solvent was a hard-sphere fluid, and the contact dimer of the solvent particles was the nonspherical solute. Two traditional closures, the Percus–Yevick and hypernetted-chain approximations, and three closures with bridge functions (BFs) were examined. These spatial distribution functions were compared with the results obtained by grand canonical Monte Carlo (GCMC) simulations. Three closures with BFs, such as the modified hypernetted-chain (MHNC) closure using a bridge function proposed by Kinoshita, gave precise spatial distribution functions. These results were much more accurate than those obtained by the traditional closures. The deviations from the spatial distribution function obtained by the GCMC simulation appeared only near the concave surface of the solute dimer. However, the deviations were minor compared with those between the simulation and the predictions of the two traditional closures. By contrast, the three-body correlation functions for the closures with BFs were not more accurate than those obtained by the traditional closures.

Refinement of Kelvin equation for condensation of water in CSH slits based on molecular simulation

The adsorption and condensation of water molecules in the pores of cementitious materials play a crucial role in the mechanical performance and durability of concrete. The Kelvin equation is generally employed to describe the water condensation in porous materials. However, it requires modification for condensation behavior in nano and micro scales of pores. In the present work, various widths of slit models for several cementitious minerals were established. The adsorption isotherms in slit pores were calculated using the hybrid of Grand Canonical Monte Carlo and Molecular Dynamics simulations, obtaining the relationship between the critical pressures for condensation and pore sizes. Then, a modified Kelvin equation was proposed, with discussion on a new reasonable method for determining the real thickness of adsorbed water film. The results demonstrate that condensation will occur in the slits within the critical width range, which promotes the surface adsorption to achieve complete adsorption. Therefore, the location of the interface between the adsorbed water film and condensed water bulk is fixed in the same mineral during condensation. The modified Kelvin equation shows higher accuracy than traditional Kelvin equations at the nano and micro scale. This work promotes a deeper understanding of the interaction mechanism of water with cementitious minerals and inspires more fundamental realization in the design of concrete durability.

Liquid-liquid transition in a simple model fluid with competitive interactions

The possible existence of low-density and high-density fluid phase equilibria in fluids with a simple potential consisting in a combination of a square shoulder and a square well is explored by means of perturbation theory and histogram-reweighting grand canonical Monte Carlo simulation. Theory is useful as a simple and computationally inexpensive way to explore large sets of potential parameters to search for potential shapes susceptible to present multiple fluid phases, later confirmed or discarded from computer simulation. It is found that some combinations of the length and energy parameters of the potential actually give rise to such behaviour.