Fig. 1: Molecular orbitals.
From: Neutral 4π-electron tetrasilacyclobutadiene contains unusual features of a Möbius-type aromatic ring

Schematic representation of the π MOs of cyclobutadiene.
From: Neutral 4π-electron tetrasilacyclobutadiene contains unusual features of a Möbius-type aromatic ring
Schematic representation of the π MOs of cyclobutadiene.