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Downloahough the orthorhombic structure is the actual ground state. A recent tudy from our group12 indicated that there is little reason to believe the rthorhombic structure can be stabilized on the basis of size or elec-rostatic effects. Another reason for the stability of this structure in iMnO2 therefore must be sought. Mn3+ ions introduce two particular features which may distinguish iMnO2 from other lithium-metal oxides. In its high-spin configura-ion, Mn3+ has four unpaired electrons with parallel spin, giving the ion large magnetic moment. Magnetic interactions in manganese oxides an, therefore, be an important factor in deciding the energy difference etween different structures. In addition to the strong magnetic inter-ction between Mn3+ ions, a strong electron lattice coupling exists due o the single occupancy of a nearly degenerate eg level which leads to Jahn-Teller (J-T) distortion. This J-T distortion reduces the symme-bonds (for which the antiferromagnetic interaction is expected to be strongest). The coupling between the chains consists of an equal num-ber of ferro and antiferro bonds. This structure therefore has analogous features to that experimentally determined for the orthorhombic phase (antiferromagnetic along short Mn-Mn bonds and cancelling contribu-tions along other directions). To further investigate its relative stability we performed fully relaxed energy calculations on three other magnet-ic configurations (those of Singh25) and found them to be higher in energy (in agreement with Singh’s nonrelaxed calculations). We are not aware of any experimental determination of the spin ordering in mon-oclinic layered LiMnO2, although some recent results by Jang et al.26 indicate possible spin-glass behavior at low temperature. Results Table I shows the energies and bond lengths of monoclinic layered (C2/m) and orthorhombic (Pmmn) structures with no spin polarizationS1099-0062(99)06-081-2 CCC: $7.0