Point defects in crystals of point Yukawa particles
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We studied vacancies and interstitials in both body centered cubic (BCC) and face centered cubic (FCC) crystals of point Yukawa particles. To this end, we used Monte Carlo simulations combined with various types of thermodynamic integration and Wang Landau biasing. With these methods we determined the concentration of both defects at the phase boundaries of the system and looked at how the defects manifest themselves in the crystals. We found that the concentration of vacancies is around the same order of magnitude as the concentration of interstitials along both the fluid-BCC and the BCC-FCC/fluid-FCC phase boundary. Furthermore we found that at the BCC-FCC phase boundary the concentration of vacancies in a BCC crystal is between 2 or 3 orders of magnitude higher than the concentration in an FCC crystal. We studied and explained this concentration difference by looking at how the particles in the two crystals redistributed due to the presence of a vacancy. In the case of an interstitial we saw that the crystal structures of both FCC and BCC crystals are distorted along all the directions of the nearest neighbors of the interstitial. In the case of a BCC crystal this distortion might be indicating a crowdion, however more research is needed to draw firm conclusions.