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 func tional theory to calculate the atomic volumes of the light actinides i ncluding Fr, Ra and Ac in their low-temperature crystallographic phase s using the local density approximation (LDA) and the generalized grad ient approximation (GGA) for the exchange-correlation energy. The good agreement between the theoretical and experimental values along the S eries 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 alpha-Pu relative to alpha-Np can be ascribed to the presence of low coordinated sites in the monoclinic alpha-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. (C) 1998 Elsevier Science S.A.