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Abstract Cu-Au intermetallic alloys are classic paradigms in the history of alloy theory for studying order-disorder transition, phase stability, and so on. However, density functional theory with a generalized gradient approximation (GGA) fails to describe their formation energies and Au-rich ground states, e.g., calculated formation energies are nearly 40% smaller than experimental values. In this work, we found that these discrepancies, which are also common in other Cu-transition metal (TM) intermetallic alloys, are actually caused by the fact that GGA produces Cu-3d bands with a shallower energy level than the experimental results, leading to incorrect d-d hybridizations. By using the Hubbard U correction to adjust the d-bands to the correct position, the discrepancies in GGA calculations are eliminated. Our finding that the correct d-bands position is the key to characterize Cu-TMs, which can be achieved efficiently by applying the Hubbard U correction.