ACCURATE FINITE-ELEMENT MULTIGRID (FEM-MG) DESCRIPTION FOR ANGULAR-MOMENTUM AND SPIN DEPENDENCES OF KOHN-SHAM DENSITY FUNCTIONALS FOR AXIALLY RESTRICTED CALCULATIONS ON FIRST-ROW ATOMS AND DIMERS

A comparative study of various combinations of exchange and correlatio n density functionals was made possible by the finite element multi-gr id method which has a controlled accuracy and became fast enough for l arge-scale applications on atoms and diatomic molecules under axial sy mmetry. The open-shell atoms B, C and O exhibit particularly interesti ng behaviour on occupation number variation, differing strongly in a s pin polarized and unpolarized approach. In the molecule C-2, the singl et ground state and the triplet excited state are characteristically d ifferently well described, independent of the specific density functio nal. A symmetry dilemma of present density functionals carried on from atoms to the C-2 dimer becomes obvious. (C) 1998 Elsevier Science B.V . All rights reserved.