Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Role of electronic correlations in the Fermi surface formation of
  Na$_x$CoO$_2$   Band structure of metallic sodium cobaltate Na$_x$CoO$_2$ ($x$=0.33, 0.48,
0.61 0.72) has been investigated by local density approximation+Hubbard $U$
(LDA+$U$) method and within Gutzwiller approximation for the Co-$t_{2g}$
manifold. Correlation effects being taken into account results in suppression
of the $e'_g$ hole pockets at the Fermi surface in agreement with recent
angle-resolved photo-emission spectroscopy (ARPES) experiments. In the
Gutzwiller approximation the bilayer splitting is significantly reduced due to
the correlation effects. The formation of high spin (HS) state in Co $d$-shell
was shown to be very improbable.

3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
17
The categories of this paper are: q-fin
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
24
The categories of this paper are: dg-ga
13
The categories of this paper are: quant-ph