[en] Highlights: • The week CH⋯OC hydrogen bonds of crystalline PHB were studied by using BOMD. • The CH⋯OC interactions are not a stable along MD simulations. • The 1D oxygen potentials were calculated, and shown good agreement with the experimental IR data. In this letter we present results of study of weak CH⋯OC hydrogen bonds of crystalline poly-(R)-3-hydroxybutyrate (PHB) by using Born-Oppenheimer molecular dynamics. The polymeric structure and IR spectra of PHB result from the presence of the weak hydrogen bonds. We applied the post-molecular dynamics analysis to consider a CO motion as indirectly involved in the hydrogen bonds. Quantization of the nuclear motion of the oxygens was done to perform detailed analysis of the strength and properties of the CO bands involved in the weak hydrogen bonds. We have also shown the dynamic character of the weak hydrogen bond interactions.