Relative energies from unrestricted Hartree-Fock (UHF) calculations for sev
eral spin and orbital orderings in CaMnO3 and LaMnO3 in cubic and tetragona
lly distorted perovskite structures are rationalised using the Goodenough m
odel. Comparison of relative energies from several calculations leads to an
estimate that the antiferromagnetic coupling energy exceeds the ferromagne
tic coupling energy per Mn ion by similar to 10 meV in both CaMnO3 and LaMn
O3. (C) 2000 Elsevier Science B.V. All rights reserved.