Quenching of magnetism in NaO 2 due to electrostatic interaction induced partial orbital ordering.

Autor: Biswas S; Department of Physics, Barasat Government College, Kolkata-700124, West Bengal, India.; Department of Physics, West Bengal State University, Kolkata-700126, West Bengal, India., De Raychaudhury M; Department of Physics, West Bengal State University, Kolkata-700126, West Bengal, India. molly.deraychaudhury@gmail.com.
Jazyk: angličtina
Zdroj: Journal of molecular modeling [J Mol Model] 2021 Dec 23; Vol. 28 (1), pp. 13. Date of Electronic Publication: 2021 Dec 23.
DOI: 10.1007/s00894-021-05008-4
Abstrakt: The transport properties of sodium superoxide (NaO 2 ) are governed by the transfer of charge between O 2 - complexes. Although it goes through a plethora of structural phase transitions, its electronic and magnetic ground state remains shrouded in mystery. In this work, we perform first-principles density functional theory (DFT) calculations to understand the relationship between electronic structure and the reason for the non-observation of an antiferromagnetic (AFM) ground state in NaO 2 vis-a-vis in KO 2 . In the cubic phase, uniform < Na-O-Na bond angles result in high symmetry and hence degeneracy in the O-2p orbitals. The freely rotating O 2 - molecules result in orbital degeneracy and hence paramagnetism at room temperature. Although the degeneracy between the bonding and anti-bonding orbitals of O 2 dimers is lifted in the pyrite phase, the degeneracy between σ (σ * ) and π (π * ) states is still maintained and hence orbital degeneracy is partially lifted as the dimers are restricted to four directions now. The O-π * states are localized in such a manner that results in a substantial magnetic moment in the π * -orbital. The < O-Na-O bond angle (= 180°) in the c-axis facilitates a superexchange mechanism and thereby the system should be AFM in the pyrite phase. In the marcasite phase, the O-atoms are aligned parallel in alternative planes. The preservation of degeneracy among the two π * orbitals leading to only long-range orbital ordering negates any chance of quasi-one-dimensional AFM spin chains in NaO 2 . The difference in magnetic ground states of NaO 2 and KO 2 arises due to the difference in the electrostatic repulsion between electrons of Na + and K + ions with the O 2 - dimers.
(© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)
Databáze: MEDLINE
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