The physical model of the formation of grown-in microdefects in dislocation-free Si single crystals has been analyzed. The mathematical models used to describe the processes of defect formation in crystals during their growth are proven to be adequate to the physical model. A technique is proposed to determine and calculate the defect structure in dependence of the crystal growth conditions (growth technique, growth rate, temperature gradients, cooling rate). It is shown that the theoretical study of the real crystal structure in the dependence of the thermal growth conditions using an original virtual technique for analyzing and calculating the formation of grown-in microdefects is a new experimental technique.