We reproduce the Debye process in the dielectric response of liquid 1-propanol by all-atom molecular dynamics simulations between 340 K and 200 K. The analysis of dipolar correlations reveals that the $\alpha$ relaxation originates from hydrogen-bond (HB) breaking, while the dominant Debye process results from long-ranged cross-correlations extending over several molecular diameters. By separating intra- and extracluster contributions, we demonstrate that HB supramolecular clusters account for the main part of the static dielectric response, with extracluster molecules playing only a minor role at low temperatures. Besides, clusters do not preserve connectivity on timescales exceeding the $\alpha$ relaxation time. This indicates that clusters stabilize orientational correlations beyond individual molecular relaxation times by transmitting alignment to newly incorporated molecules. These findings provide microscopic evidence that the Debye relaxation in monoalcohols arises from the collective dynamics of HB clusters and offer a framework to study dielectric spectra in other hydrogen-bonded liquids.

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• Dielectric properties
• Hydrogen bonds
• Liquids
• Dielectric spectroscopy
• Molecular dynamics