Local density approximation versus generalized gradient approximation: full charge density study of the atomic volume of the light actinides

We have used a full charge-density technique based on the density functional theory to calculate the atomic volumes of the light actinides including Fr, Ra and Ac in their low-temperature crystallographic phases using the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation energy. The good agreement between the theoretical and experimental values along the series support the picture of itinerant 5f electronic states from Th to Pu. The comparison between the LDA and the GGA results shows that the anomalously large atomic volume of α-Pu relative to α-Np can be ascribed to the presence of low coordinated sites in the monoclinic α-Pu structure, where the f-electrons are more localized and the charge density is very low in the interstitial region. In this system the exchange-correlation effects can be correctly described using the GGA but not within the LDA. (orig.)