ORBITAL AND MAGNETIC ORDERINGS IN LOCALIZED T(2G) SYSTEMS, YTIO3 AND YVO3 - COMPARISON WITH A MORE ITINERANT E(G) SYSTEM LAMNO3

The electronic structures of the narrow t(2g) band systems YTiO3 and Y VO3 are studied using the generalized gradient approximation (GGA) and local-density approximation (LDA)+U method. GGA fails in reproducing the insulating nature of YTiO3 and the correct magnetic ordering of YV O3. The LDA+U method improves the GGA results in both;of the above con texts through the enhancement in the orbital polarization. These resul ts are compared with those for the wider tig band system LaVO3 and mor e itinerant e(g) system LaMnO3. The problems of GGA and LDA+U in predi cting the ground-state magnetic ordering of LaMnO3 will also be discus sed.