  A parameter-free, mean-field, multi-orbital Hubbard model with nonspherical
Coulomb and exchange interactions, implemented around all-electron
local-density approximation (LDA) calculations, correctly predicts the band-gap
energy, the absence of dimerization, and the antiferromagnetic ground state of
halogen-bridged linear-chain Ni compounds. This approach also reproduces the
insulating ground state and dimerization in PtX linear-chain compounds in
agreement with experiment and previous calculations. Three "ps" figures are
included at the end of the RevTex file and compressed using uufiles.
