  The standard model of classical Density Functional Theory for pair potentials
consists of a hard-sphere functional plus a mean-field term accounting for long
ranged attraction. However, most implementations using sophisticated
Fundamental Measure hard-sphere functionals suffer from potential numerical
instabilities either due to possible instabilities in the functionals
themselves or due to implementations that mix real- and Fourier-space
components inconsistently. Here, we present a new implementation based on a
demonstrably stable hard-sphere functional that is implemented in a completely
consistent manner. The present work does not depend on approximate spherical
integration schemes and so is much more robust than previous algorithms. The
methods are illustrated by calculating phase diagrams for the solid state using
the standard Lennard-Jones potential as well as a new class of potentials
recently proposed by Wang et al (Phys. Chem. Chem. Phys. 22, 10624 (2020)). The
latter span the range from potentials for small molecules to those appropriate
to colloidal systems simply by varying a parameter. We verify that cDFT is able
to semi-quantitatively reproduce the phase diagram in all cases. We also show
that for these problems computationally cheap Gaussian approximations are
nearly as good as full minimization based on finite differences.
