the question about ddg of disulfide bond mutants

I want to evaluate the ddg between WT and  disulfide bond mutants 

1. I try to use ddg_monomer and fond it does not suport it

2. Then I build disulfide bond mutants with moddler, and then  try to use ddg_monomer to evaluate  the ddg ( mutant  CYS  recovery to the amino acid of WT), and it does not work , too.

3. Just as 2.  I try to use another APP, cartesian_ddg ， and  disulfide bond mutants as the star model，and  ddgs seem is similar(just try three mutant)

How can I evaluate the ddg between WT and  disulfide bond mutants ? Thanks