We have performed full charge-density calculations for the equilibrium atomic volumes of the {alpha}-phase light actinide metals using the local density approximation (LDA) and the generalized gradient approximation (GGA). The average deviation between the experimental and the GGA atomic radii is 1.3{percent}. The comparison between the LDA and GGA results show that the anomalously large atomic volume of {alpha}-Pu relative to {alpha}-Np can be ascribed to exchange-correlation effects connected with the presence of low coordinated sites in the structure where the f electrons are close to the onset of localization. This effect is correctly described in the GGA but not in the LDA. {copyright} {ital 1997} {ital The American Physical Society}