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Using first principles LSDA+U calculation, a systematic investigation of the role of the Hubbard potential U on the structural, magnetic and electronic properties of Co 2 TiSi and Co 2 TiSn Heusler alloys was conducted. The structural, magnetic and electronic properties of Co 2 TiSi and Co 2 TiSn were calculated at different values of Hubbard potentials for Co ( U Co ) and Ti (U Ti ) atoms. The calculated lattice parameters are found to be slightly underestimated when compared with the experimental values with insignificant dependence on both U Co and U Ti . While non integer magnetic moments and metallic behaviors were predicted by LSDA, LSDA+U predicted half metallic behaviors and magnetic moments of 2μ B , in agreement with Slater-Pauling rule, at relatively low values of U Co and U Ti . A strong dependence of the band gap ( E g ) on U Co and U Ti was found in the two systems. The E g ( U ) dependence is characterized by two distinct regions: first region shows increasing trend while second region shows saturation with the increase in the value of U Co . In the first region, the band gap is controlled by Co d - t 2g and Co d - e g suborbitals only, and U Ti plays no role in agreement with Glanakis et al. scheme. However, in the second region, the band gap is defined by the Co d - t 2g and Ti d - e g suborbitals. The band gaps of the alloys were also calculated using the modified Becke-Johnson (mBJ) method predicting values within the second regions. The role of U Co and U Ti in determining the E g of the two systems was discussed. [ABSTRACT FROM AUTHOR]