recognized functionals; systematic naming
We should find systematic names for the vdw functionals in a way consistent with libxc.
Like gga_x_pbe, except for vdw.
For example NOMAD uses these codes:
vdW-DF: gga_x_pbe_r + vdw_c_df1 vdW-DF2: gga_x_rpw86 + vdw_c_df2 vdW-DF-CX: gga_x_lv_rpw86 + vdw_c_df_cx
These names were suggested (or at least approved) by Micael Oliveira.
(In NOMAD, the correlation is taken to include LDA correlation, but that is probably not the best in the long run.
Better option may be e.g.
gga_x_lv_rpw86 + lda_c_pw + vdw_c_df_cx.
Then we should recognize all the versions/variants under such a name.