Electronic Structure, Chemical Bonding, and Vibronic Coupling in MnIV/MnIIIMixed Valent LixMn2O4Spinels and Their Effect on the Dynamics of Intercalated Li: A Cluster Study Using DFT

Abstract

Density functional theory (DFT) calculations on the MnIV7O14 and MnIII/MnIV mixed valent Mn7O14- clusters are reported and used to characterize the Mn−O bonding in LixMn2O4 spinel. A recipe is proposed of how to extract from calculations on clusters electronic hopping and charge transfer (CT) energy parameters and to use them in a semiempirical (Hubbard type) Hamitonian which simultaneously accounts for electronic correlation and translational symmetry. The first application of this approach to Mn2O4 shows that, in contrast with conventional band calculations, the 3d electrons of Mn are rather localized. Vibronic coupling due to the 2t2g32eg1 configuration of MnIII with the α1g and the Jahn−Teller(JT) active eg modes is analyzed using DFT calculations of the mixed valent Mn7O14- cluster and is found to lead to a lengthening of the Mn−O bond and to tetragonally elongated octahedra accompanied by an appreciable stabilization energy(−0.445 eV). Vibronic coupling and electron hopping energies obtained from th...