  The local intermolecular structure and related dynamics in the liquid
cis-trans N-methylformamide mixture at ambient temperature and density
conditions have been systematically studied by employing Born-Oppenheimer
molecular dynamics simulation techniques. Particular attention has been paid to
the local structure around the cis- and trans- conformers and the formation and
dynamics of hydrogen bonds with their closest neighbors. The calculated
atom-atom radial distribution functions are in very good agreement with
available experimental data and reveal the existence of different types of
hydrogen bonding intermolecular interactions. The average number of hydrogen
bonds formed by the cis-conformers is higher in comparison with the one
corresponding to the trans-conformers. Moreover, the lifetimes of the hydrogen
bonds formed in the liquid are longer when the cis-conformers participate in
the bond formation, either as donors or acceptors. These findings clearly
indicate that the local structural network around the cis-conformers in the
liquid is more cohesive. The latter finding is also reflected in the slower
reorientational dynamics of the cis-conformers and the low- and high-frequency
region of the spectral densities of the atomic velocity time correlation
functions. Finally, the calculated average dipole moments of the trans- and
cis- conformers are significantly higher than their corresponding gas-phase
values, signifying the importance of polarization effects in this particular
polar liquid solvent.
