Table 1. Expected k points of the conduction band minimum (CBM) and valence band maximum (VBM) for all possible combinations of B and B′ orbitals. Note that the VBM and CBM must be evaluated separately for a given perovskite.

Orbitals		Prediction
B	B′	VBM	CBM
σ-Bonding states a
s	s	Γ	Γ
p	p	Γ	Γ
dx2–y2/dz2	dx2–y2/dz2	Γ & X	Γ & X
s	p	L	L
s	dx2–y2/dz2	X	X
p	dx2–y2/dz2	—	—
s	Null	X	Γ
p	Null	L	L
dx2–y2/dz2	Null	Γ & X	X
Null	Null	Γ & X	—
π-Bonding states a
dxy/yz/xz	dxy/yz/xz	Γ & X	Γ & X
dxy/yz/xz	Null	X	Γ & X
Null	Null	Γ b	—

^aπ- and σ-bonding states involve orthogonal orbitals and cannot interact (see ESI).

^bThe σ-bonding halide-only states have more 90° X–X interactions than the π-bonding ones and will often form the band extrema (see ESI).