  Clarifying the origin of nematic state in FeSe is one of urgent problems in
the field of iron-based superconductivity. Motivated by the discovery of a
nematic solution in the density-functional theory implemented by on-site
Coulomb interaction (DFT+$U$) [npj Quantum Mater. \textbf{5}, 50 (2020)], we
reexamine the $U$ dependence of electronic states in the nonmagnetic normal
state of FeSe and perform full multipolar analyses for the nematic state. We
find that with increasing $U$ the normal state experiences a topological change
in the Fermi surfaces before the emergence of a nematic ground state. The
resulting nematic ground state is a multipolar state having both
antiferrohexadecapoles in the $E$ representation and ferromultipoles in the
$B_2$ representation on each Fe site. Cooperative coupling between the $E$ and
the $B_2$ multipoles in the local coordinate with the $D_{2d}$ point group will
play an important role in the formation of the $d_{xz},~d_{yz}$
orbital-splitting nematic state not only in FeSe, but also in other iron
pnictides.
