It was found that the ground state of the carbon cluster C-28 Of Td symmetr
y; is quintet having negative spin-densities. Another cluster C-48 Of Oh sy
mmetry manifests different instabilities but has the singlet groundstate Ag
-1 With alternation of bond lengths. The fee lattices for solid C-28 doped
by alkali-earth elements are examined and peculiarities of nonlinear optica
l property calculation of C-48 are discussed. (C) 1999 Elsevier Science B.V
. All rights reserved.