Hydrogen atom transfer (HAT) reactions were calculated using QM/MM calculations for the representative snapshots from MD simulations. In CYP450BM3, the QM-region involves substrate NPG and heme, whereas, the QM region of peroxygenases CYP450OleT and CYP450BSβ include truncated heme-porphyrin, truncated substrates, and R245/R242, H85/Q85 and two water molecules. The active region in QM/MM calculations in all the systems involves the protein residues and water molecules present within the cutoff of 8Å from the active oxidant heme. The atoms in the selected "active region" (mainly from the MM part) interact with the QM zone through electrostatic and van der Waals interactions and the corresponding polarization effects were considered in the subsequent QM/MM calculations. All QM/MM calculations were performed with ChemShell, by combining the Turbomole for the QM part, and DL_POLY for the MM part. The MM part was described using ff19SB forcefield. To account for the polarizing effect of the protein environment on the QM region, an electronic embedding scheme was used.