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First principles calculations based on density functional theory (DFT) using TB-mBJ and SCAN + U methods were used to study the electronic and optical properties of the monoclinic VO 2 (M1) phase. TB-mBJ gives values of the energy gap (E g) and Δd || band splitting in agreement with experiments. Systematic investigation of SCAN + U, U varies from 0 to 10 eV, shows that agreement with experimental values of both E g and Δd || was achieved at U * = 5.75 eV. Moreover, TB-mBJ and SCAN + U * were able to reproduce frequency and polarization dependence of the optical constants that agree with the reported experimental results of the monoclinic VO2 (M1) phase. The high value of U needed to reproduce the experimental values of electronic and optical parameters of the monoclinic VO 2 (M1) phase is a strong indication that VO 2 is a Mott insulator and the Mott-Hubbard scheme plays an important role in the metal-insulator transition. • The electronic and optical properties of the insulating monoclinic VO 2 (M1) phase were studied using TB-mBJ and SCAN+ U. • The size of the energy gap (E g) and d || band splitting and some optical constants of the VO 2 (M1) phase were calculated. • TB-mBJ and SCAN+U gave E g and Δd|| band splitting values in agreement with experiments. • TB-mBJ and SCAN+U were able to predict the frequency and polarization dependence of n , a , ε 1 , ε 2 of the VO 2 (M1) phase. • The current calculations reveal that Mott-Hubbard electron correlation is dominant in the metal-insulator transition in VO 2. [ABSTRACT FROM AUTHOR]