Geometrical, electronic, and magnetic properties of Na 0.5 CoO 2 from first principles
2005; American Physical Society; Volume: 71; Issue: 2 Linguagem: Inglês
10.1103/physrevb.71.024502
ISSN1550-235X
AutoresZhenyu Li, Jinlong Yang, Jian Hou, Qingshi Zhu,
Tópico(s)Advanced Condensed Matter Physics
ResumoWe report a first-principles projector augmented wave (PAW) study on ${\mathrm{Na}}_{0.5}{\mathrm{CoO}}_{2}$. With the sodium ion ordered insulating phase being identified in experiments, pure density functional calculations fail to predict an insulating ground state, which indicates that $\mathrm{Na}$ ordering alone cannot produce accompanying $\mathrm{Co}$ charge ordering if additional correlation is not properly considered. At this level of theory, the most stable phase presents ferromagnetic ordering within the ${\mathrm{CoO}}_{2}$ layer and antiferromagnetic coupling between these layers. When the on-site Coulomb interaction for $\mathrm{Co}$ $3d$ orbitals is included by an additional Hubbard parameter $U$, a charge ordered insulating ground state can be obtained. The effect of on-site interaction magnitude on electronic structure is studied. At a moderate value of $U$ ($4.0\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, for example), the ground state is antiferromagnetic, with a ${\mathrm{Co}}^{4+}$ magnetic moment about $1.0\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}$ and a magnetic energy of $0.12\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{Co}$. The rehybridization process is also studied in the $\mathrm{DFT}+U$ point of view (where DFT represents density functional theory).
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