The FFT Poisson solver 3D-0D was not correct for non-orthogonal cells.

Description

The FFT Poisson solver 3D-0D was not correct for non-orthogonal cells. The code now uses the cutoff energy to set the right Coulomb cutoff.

The result now agrees with the direct solver for NiO, Si, LiF, and Sb2Te3.

Thanks to @IteLu for finding this.

News snippet

Bugfix for the calculation of the Coulomb integrals used to get the ab initio U.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.