For starters, you'll need a fairly diffuse basis set (so ++ ) in order to give the extra degrees of freedom to the Lagranga multipliers to be able to manipulate the electron density.
Even then, converging the CDFT at large separations is an issue. One thing I planned to do, but never quite got around to, was adding 'ghost' atoms between the D / A molecules with no charges but with atomic-centered basis, in order to give extra freedom.
Convergence is fairly tricky, but is possible.
For starters, you'll need a fairly diffuse basis set (so ++ ) in order to give the extra degrees of freedom to the Lagranga multipliers to be able to manipulate the electron density. Even then, converging the CDFT at large separations is an issue. One thing I planned to do, but never quite got around to, was adding 'ghost' atoms between the D / A molecules with no charges but with atomic-centered basis, in order to give extra freedom.