We carried out calculations to determine whether the adoption of the [100] orientation can be explained thermodynamically, as we have demonstrated in our previous work on other symmetry QII phases. We have shown previously that the orientation of 𝑄 𝐼𝐼 𝐷 and 𝑄 𝐼𝐼 𝐺 phase films can be predicted by calculating the relative energy with the plane of the film lying in different crystallographic orientations relative to the cubic unit cell. This energy is calculated by minimizing the free-energy functional for the system where the surface at the centre of the bilayer remains continuous and so caps off one water channel network. This process deforms the structure, which carries an energetic cost. The lowest energy orientation predicted for the 𝑄 𝐼𝐼 𝐷 and 𝑄 𝐼𝐼 𝐺 phases, with respectively (111) and (110) planes parallel with the interface, was indeed the orientation observed in GI-SAXS experiments. In this work, we performed equivalent calculations for the 𝑄 𝐼𝐼 𝑃 phase (see Methods). The energy functional was the same as in previous analysis of the 𝑄 𝐼𝐼 𝐷 and 𝑄 𝐼𝐼 𝐺 phases but with the following nodal approximation for the initial configuration of the field ϕ(r) representing a 𝑄 𝐼𝐼 𝑃 phase (Equation ):