On the stability and dynamics of (sulfuric acid) (ammonia) and (sulfuric acid) (dimethylamine) clusters: A first-principles molecular dynamics investigation

- At T = 300 K the clusters show pronounced thermal vibrations and rotations.
- Regardless of the molecular motion, the clusters stay bound together.
- The electric dipole moments are very sensitive to the thermal motion.
- Molecular vibrations and rotations are clearly anharmonic.

The main pathway of new-particle formation in the atmosphere is likely to begin from small sulfuric acid clusters stabilized by other compounds, such as ammonia or amines. Here, we present the results of first-principles molecular dynamics simulations probing the stability and dynamics of (sulfuric acid) (ammonia/dimethylamine) clusters with two, three and four sulfuric acid molecules and a varying number of the bases. In each of the eight simulated clusters, an energetic equilibrium was reached and 35 ps of equilibrium data was collected in the NVT(T=300 K) ensemble. The clusters exhibited pronounced thermal motion including rotations of the molecules within the clusters. Regardless of the continuous movement, the clusters stayed bound together. The calculated electric dipole moments were found to be sensitive to the thermal motion and consequently, large fluctuations were observed. In addition, the vibrational spectra for all the clusters were determined, indicating that the thermal motion differs from purely harmonic motion.