  We show that generalized spherical harmonics are well suited for representing
the space and orientation molecular density in the resolution of the molecular
density functional theory. We consider the common system made of a rigid solute
of arbitrary complexity immersed in a molecular solvent, both represented by
molecules with interacting atomic sites and classical force fields. The
molecular solvent density $\rho(\mathbf{r},\mathbf{\Omega})$ around the solute
is a function of the position $\mathbf{r}\equiv(x,y,z)$ and of the three Euler
angles $\mathbf{\Omega}\equiv(\theta,\phi,\psi)$ describing the solvent
orientation. The standard density functional, equivalent to the HNC closure for
the solute-solvent correlations in the liquid theory, is minimized with respect
to $\rho(\mathbf{r},\mathbf{\Omega})$. The up-to-now very expensive angular
convolution products are advantageously replaced by simple products between
projections onto generalized spherical harmonics. The dramatic gain in speed of
resolution enables to explore in a systematic way molecular solutes of up to
nanometric sizes in arbitrary solvents and to calculate their solvation free
energy and associated microscopic solvent structure in at most a few minutes.
We finally illustrate the formalism by tackling the solvation of molecules of
various complexity in water.
