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Keywords:

  • aggregation;
  • amides;
  • conformation analysis;
  • hydrogen bonds;
  • molecular dynamics

Abstract

The formation of formamide trimers was simulated using Car–Parrinello molecular dynamics. A variety of different initial setups were compared to study the effects of spatial arrangement, concentration, and temperature on the trimer product distribution. A total of nine different trimer species were obtained by simulation. Although a triangular initial arrangement of the three monomers is found to favour a less energetically stable chain-like product at high concentration, the more compact global minimum structure is expected to be the most abundant species overall in experiment. This is because there is evidence of a low activation barrier for conversion of the chain-like trimer to the lowest-energy structure. For one, this process is observed upon increasing the length of the trajectories. Furthermore, a slight rise in temperature drastically reduces the number of chain-like trimers. With regard to the intermolecular forces driving the aggregation dynamics, dispersion corrections to the underlying density functional theory description have a strong effect on the product distribution, again favouring the global minimum species. Certain local minimum structures are significantly destabilised relative to the global minimum by dispersion correction while the relative energies of the majority of species are practically unchanged.