Material Crystallinity Theoretical Predictions

Materials of single crystal structures exhibit a lot of superior properties, and continuous efforts have been made to prepare single crystals with larger volume and better structure. In practice, different materials show considerable difference in the ability to form single crystals. Then predicting the ability of the materials to form single crystal structure is of high importance besides concerns about their structural and physical properties.However, no theory, up to now, is available for evaluating the ability of materials to form single crystal structure. Binding energy, which is widely used in material design, fails to work on this issue as it cannot tell the difference in the ability of a material to form single crystal on the different crystal surfaces. Phase field model, a powerful tool to investigate the macroscopic dendrite growth, also fails to predict this ability, because the parameters involved in this model cannot be reliably calculated for practical materials.In this work, we tried to find a simple theoretical method to evaluate the ability of the materials to form single crystal structure. A concept named as "condensing potential"(CP) was introduced to describe the energy potential near the crystal surface, while another concept named as "fault degree"(FD) was used to evaluate the quantities of newly grown crystal. By performing extensive molecular dynamics simulation, we found that FD increases monotonously as decreasing CP in materials with all fcc, bcc and hcp structures. In addition, we examined the relationship between CP and the melting points of materials, and found that a higher melting point is corresponded to higher CP.It should be noted that, although only empirical potentials were employed in this study, the conclusion we obtained should be independent of the accuracy of the empirical potentials, as the same potentials were used in both the calculation of CP and FD. It is more significant that CP can be simply calculated by common ab-initial calculation package, which makes our method a convenient and accurate tool to evaluate the ability of the materials to form single crystal structure.