The physical properties of point defects in Si crystal have not been established with certainty. That makes it difficult to calculate the behavior of grown-in defects in CZ Si crystal growth. With high-precision thermal analysis we studied the physical properties of point defects from which the grown-in defects distribution could be calculated. In this study we focused the attention on the V-I boundary in which the vacancy and self interstitial concentrations are balanced, which appears in case of slowly decreasing the crystal growth rate. we assumed that the determination of the physical properties was an optimization problem, and we applied a genetic algorithm method and a simulated annealing method. In addition, we examined the optimized physical properties with physical considerations and reproducibility of V-I boundary shape in calculation. As a result, we estimated one promising set of the physical properties, which were used to calculate the grown-in defect distribution. The calculation result showed that (1) it could reproduce the experimental results and (2) the concentration difference (ΔC) between vacancy and self interstitial was related to grown-in defect types.