# Molecular Dynamics Simulation of Bulk Cu Material under Various Factors
## 1 Introduction
[40] applied MD simulations to determine the tensile deformation of gradient nano-grained copper film films. In addition, MD has been widely applied to determine the structure and thermodynamic properties of metals [41], especially for the structural phase transition of single-crystal Cu [42]. Cu is a metal with a face-centered cubic (FCC) crystal structure, and it is very stable until it changes to the liquid state [43]; its structure change is based on the phase transition diagram. The body-centered cubic (BCC) phase of Cu is unstable in the ground state [44] (demonstrated by the Ab--Initio method), which has led to controversy and various explanations. In addition, stable substrates with complex structures that affect Cu structure only occur in thin films and not in bulk materials or materials that are thick films [45]. [PERSON] [46] demonstrated that the BCC structure of Cu is energetically unstable in the ground state but is suitable for high temperatures because of its large entropy and its low-energy transverse vibrational mode. This fact highlighted that the structural transformation can be driven only by an excess of the fluctuating entropy of the high-temperature phase [47]. Given the importance and extensive applications of Cu, this element has been extensively studied in different research [48; 49; 50]. In addition, it has been determined that the phase transition temperature (T\({}_{\rm m}\)) of the material decreases with decreasing size [51; 52], and the appearance of cubic structure units and crystallization was found at room temperature [53]. As has been emphasized above, MD methods have been widely used in studies on structural evolution during crystallization [54], deformation characteristics, and the stress-strain response [55]. [PERSON] et al. [56] argued that there is little research regarding the crystallization of amorphous materials in which stress plays a very important role. Recently, some researchers [57] considered the structure of materials by analyzing the structure of chemical bonds between atoms that were constituents of the given condensed matter. They used an abstract set theory with the concept of topological Hausdorff-Besicovitch dimension, which has a stepwise change from zero to fractal one (nearly 2.55), when the condensed system passes the glass transition temperature T\({}_{\rm g}\). Thus, above this temperature, the structure of the system has fractal symmetry, evidently different from 3D. This leads to an important conclusion: phase transitions of Cu at this point have a topological character, quite different from that related to spontaneous breaking of traditional symmetries, such as translation and rotation. Then, the authors proposed a method for fixing the glass transition temperature using the procedure they discovered earlier in [58; 59], which led to the result of 794 K. This is a higher than the value of 773 K obtained from the well-known Wen-Abraham empirical criterion given in [60]. These values are also different from the result of 652 K obtained in this paper by our simulation method, which, in our opinion, is more in agreement with reality because it is a result of the fast convergent MD simulation procedure presented below. Notably, in Cu material, there is a change in the number of FCC, hexagonal close-packed (HCP), BCC, and amorphous (Amor) structural units [61], with a transition hot temperature of T\({}_{\text{m}}\) = 1356.2 K [62]. In addition, the material size, energy, and number of atoms influences the structural characteristics, electronic structure, and phase transition of the metals Al [63], Fe [64], and Ag [65] and the alloys AlNi [66], NiCu [67; 68], AgAu [69], NiFe [70], AuCu [71], NiAu [72], and CuAu [73]. Therefore, the question arises of whether there is any influence on the structure, phase transition, and the phase transition temperature of the bulk Cu material.