.. _PI:

``PI``
======

The normal density matrix is composed of atomic orbitals, that is *s*,
*p*\ :sub:`x`, *p*\ :sub:`y` and *p*\ :sub:`z`. ``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 sp\ :sup:`2` hybridized system
would be represented as *s-σ*: 1.0, *p-σ*: 2.0, *p-π*: 1.0.