Electronic property and effective diffusion coefficient calculation model of hydrogen isotopes in multicomponent steel 2.25Cr1Mo from first-principles calculations

•Interaction between H and 2.25Cr1Mo was a combination of ionic and covalent bonds via first-principles calculations.•Cr and Mo dopants localized the interaction between H and Fe matrices and they acted as scattering centers for H isotopes diffusion with high energy barriers.•Voigt and Reuss models were proposed to calculate effective H isotopes diffusion coefficients of 2.25Cr1Mo for the first time which agreed with experiments results.•Reliable way to determine effective diffusion coefficient of hydrogen isotopes in multielement alloys was established.