* The two values in each box for the 3b structure correspond to the Xe-Au1 and Xe-Au3 bonds, respectively.

The bonding character of Ng-Nm interactions has been one of hot issues of the related research field. To further explore the chemical bonding nature of Xe-Au bonds in Xe(AuF)_n (n = 2-4), quantum-theory-of-atoms-in-molecules (QTAIM) analysis is performed, aimed at providing extra evidence for a bond path among all bonding interactions with a bond critical point (BCP) and a significant accumulation of electron density within the bond (see electron densityρ _bcp in Table 1 ). Typically, at the BCP of a certain chemical bond, high electron densityρ (r _c) and negative Laplacian electron density ▽²ρ (r _c) values define a covalent bond, but this criterion does not always work especially when heavier atoms are involved. The energy densityH (r _c), ratio of local kinetic energy density G (r_c ) and electron densityρ (r _c), however, are more proper parameters in these cases. Covalent bonds are characterized by BCPs with negativeH (r _c) andG (r _c)/ρ (r _c) lower than 1, while those with positiveH (r _c) andG (r _c)/ρ (r _c) exceeding 1 usually denote closed-shell interaction.^[59] Based on this criterion, theH (r _c) andG (r _c)/ρ (r _c) values at all BCPs suggest explicit covalent nature of the Xe-Au bonds for the whole series of predicted structures. Moreover, as mentioned in the RDG analysis, the electron density between Xe and Au atoms are slightly bigger in traditional structures (2b , 3c and4a ). Topological analysis was additionally performed for linear NgNmX (Ng = He, Ne, Ar, Kr and Xe; Nm = Cu, Ag and Au; X = F, Cl, Br and I) molecules and compared in Table S3 , revealing that the Ng-Nm bonds are gradually transformed from dispersive to covalent as the Ng atom grows heavier and that the metal and halogen atoms are capable of affecting the Ng-Nm bonding strength without altering the bonding character.