Subject: Electronic configuration of Co

From: Darren Simpson <[email-masked]>
Date: Fri, 21 Nov 1997 14:27:59 +1030

Hello computational chemists,

I am interested in modeling reactions at the surfaces of NiO and CoO
clusters.  I am also trying to gather information on the electronic
structure of Co in CoO.  The d electrons of these oxides are localized
on the metal atoms as found in transition-metal complexes.  Crystal
field theory used to describe the electronic structure of complexes can
also be applied to these solids.

The structure of these oxides is the rock-salt or face-centred cubic
structure and each metal atom in the bulk is surrounded by 6 oxygen
atoms in an octahedral environment.  For NiO (d8), there is only one
configuration ie t2g [dxy(2) dxz(2) dyz(2)] and eg [dz2(1) dx2-y2(1)]
thus 2 unpaired electrons per Ni atom.  At the 100 surface, t2g/eg
energy levels are distorted due to the reduction in coordination from 6
to 5.

For CoO, the electronic structure is more complex because Co (d7) can
adopt a high-spin (3 unpaired d electrons) or low-spin (1 unpaired d
electron) state.  However I am unsure of the electronic structure in the
bulk and at the surface/boundary of the CoO cluster.  Does, Co adopt a
low-spin state at the surface and high-spin in the bulk?  Any advice,
information, references etc on this topic is welcome .

A summary of responses will posted to the list.

Thanks in advance,

Darren Simpson

Ian Wark Research Institute
University of South Australia
The Levels, SA 5095
Australia

Email: [email-masked]