The cis/trans isomerization of peptidyl bonds in proline is a fundamental step of the protein folding process which often coincides with the rate-limiting step of the process, catalyzed by prolyl cis-trans isomerase (PPIase) enzymes. Considering the numerous experimental and computational studies available on the isomerization of proline-containing peptides, the cis-trans isomerization reaction involving proline (Ace-Pro-NHMe) and a proline-containing peptide (succinyl-Ala-Ala-Pro-Phe-p-nitroanilide) were chosen in a previous study as a benchmark for our PBC-adapted QM/MM MD methodology. The aforementioned systems are employed again in the current study as a benchmark of the proposed PBC-adapted DFTB/MM method and DFTB parameters.