The research in nanoparticles (NPs) has presented overwhelming development due to their importance in many fundamental applications such as catalysis, remediation, sensing, and drug delivery, among many others [1], [2], [3], [4]. Alloyed NPs have been raised as an alternative to overcome the limits on NP performance, [5], [6] to the point that many morphologies such as core–shell or Janus-like among many others have been presented [7], [8], [9], [10]. Despite of morphology, alloying has been employed as a route to tailor NP response; however, this approach is limited to the manufacturing process. Last years new kinds of materials, such as the case of high entropy alloys (HEA), raised the alternative to finish the alloys paradigm since they can mix five or more elements in equiatomic proportions to bring unexpected properties to the materials. HEA and their nanoparticle derivatives, HEA NPs, have emerged as a fascinating area of study in materials science, however, the synthesis, design, and understanding of these materials present several challenges and opportunities for future research. A comprehensive review of HEAs [11] is provided by Tsai et al. [12], discussing key aspects such as core effects, phases and crystal structures, mechanical and high-temperature properties, structural stabilities, and corrosion behaviors. These factors highlight the current challenges and potential future directions in the study of HEA. The rational design and fabrication of nanosized HEA consider the principles of element matching and the conditions for forming single-phase solid solution HEA, and computational methods for predicting the formation conditions and properties of HEA under different synthetic environments [13].

Recently the development of HEA-NPs has been raised as a new approach in NP research. The main feature is related to the different atomic sizes, which introduce internal stress modifying the electronic structure, introducing new properties due to the already known cocktail effect. Several synthesis methods have been reported to create HEA-NPs on a wide range of size and compositions [14], [15], [16], [17], [18]. While many synthesis methods have been focused on creating HEA with elements of similar atomic radius, some recent works have overcome such limitations to enlarge the possible combinations of multi-component NPs [19].

For example, Gao et al. [20] introduce a fast moving bed pyrolysis strategy for synthesizing HEA-NPs on granular supports. This strategy results in a narrow size distribution of HEA-NPs and ensures the rapid and simultaneous pyrolysis of mixed metal precursors at high temperatures. The representative quinary (FeCoPdIrPt) HEA-NPs synthesized using this method demonstrate high stability and mass activity in the hydrogen evolution reaction. Recently, Mao and coworkers report a method to synthesize spherical CoCrCuFeNi nanoparticles (NPs) with a controllable microstructure and composition using a modified plasma arc-discharge method [21]. The as-prepared NPs exhibit comparable soft magnetic features, with the asymmetric characteristic likely due to the magnetic coupling of the Cu-rich Face Centered Cubic (fcc) phase with a relatively hard magnetic BCC crystalline phase. Besides, the active sites of HEA-NPs CoCrXFeNi (X=Al, Cu, Mn) have been used for degrading methylene blue (MB) dye [22]. The study shows that HEA-NPs synthesized on activated carbon (AC) using the impregnation-adsorption method can effectively decompose MB molecules, making them a promising material for dye decomposition and mineralization.

One of the main challenges to date has been raised from characterization techniques to understand the microstructural effects product of chemical complexity and their influence on NP morphology and properties. In this aspect, many modeling techniques such as ab initio simulations, molecular dynamic (MD), and recently machine-learning [23], [24], [25] simulations have been used to understand the fundamental atomistic processes that dominate some particular physical phenomena. HEA NP has been studied by MD simulations, focusing on the diffusive process during the formation of multi-component alloys of FeCuNiCrMn and AlCoCrCuFeNi, using as precursors the respective single component NPs [26], [27]. Zeng et al. [28] studied the melting process AlCuFeCrNi HEA NP, showing that the diffusion process is not homogeneous; instead, Cr have larger diffusion during the thermal loading than the other elements. For structural characterization, Calvo [29] studied by Monte Carlo simulations the role of shape and size in the atomic distribution of different HEAs. His results do not show the direct formation of preferential planes, but it is very illustrative to explain that some surface planes promote the migrations of elements. In the same direction, Ju et al. [30] addressed the atomistic mechanism on the melting of PtPdRhCo NP different compositions, showing that the atoms with larger shear strain are confined to NP surface.

Despite each of the valuable contributions in the field, there still needs to be more understanding of the structure and properties of HEA NPs. The present work has as motivation to understand the atomic process that dominates the HEA NP structure, looking for evidence of clustering, migration, or segregation of their components. Our final goal is to understand how chemical complexity influences the structural properties of HEA NPs, which simultaneously makes them differ from mono-element or alloyed nanostructures. Between all possible HEA, FeNiCrCoCu is still subject of debate in regard of how Cu modify the HEA micro-structure. Some experimental works have shown a Cu rich fcc phase [31], [32] when Cu concentration increase over a threshold. Besides, some interesting works have synthesized 50 to 70 nm nps with an outstanding performance in methylene degradation [22].

This paper is organized as follows: after the introduction section, we describe the computational methods and techniques in Method. Next, the results obtained are given in Results, contrast with experiments results and related works is commented in Discussion, the paper is closed with Summary and Conclusions