The normal density matrix is composed of atomic orbitals, that is s, px, py and pz. PI allows the user to see how each atom-atom interaction is split into σ, π, and Δ bonds. The resulting "density matrix" is composed of the following basis-functions: s-σ, p-σ, p-π, d-σ, d-π, d-δ. The on-diagonal terms give the hybridization state, so that an sp2 hybridized system would be represented as s-σ: 1.0, p-σ: 2.0, p-π: 1.0.