A comprehensive liquid simulation study of neat formic acid
Mináry P., Jedlovszky P., Mezei M., Turi L.
An extensive liquid simulation study combining Monte Carlo and molecular dynamics techniques was performed for liquid formic acid. We investigated thermodynamic, dynamic, and spectroscopic properties of the liquid. The examination of several dynamic properties leads to a detailed picture of the molecular contributions to the macroscopic properties of the liquid phase. Although the present model overestimates the diffusion constant by about 25%, the calculated spectral densities for the translational and rotational modes of the solvent in combination with ab initio calculated harmonic frequencies provide a valuable tool in the qualitative assignment of several important features of the low-frequency liquid phase Raman spectrum. The relaxation time scales also give reasonably good agreement with dielectric relaxation and NMR measurements. Hydrogen-bonding dynamics provide interesting additional information on the dynamical time scales.-The average lifetime of the strongest types of hydrogen bonds is less than 0.5 ps. The relative population of the dimers with rivo hydrogen bonds undergoes a significant change relative to the gas phase population, the weight of the less stable dimers increasing substantially. Approximately 1% of the molecules participate in hydrogen-bonding patterns which dominate the crystalline phase of the formic acid. As an extension of the present work for the liquid phase, we have also performed calculations for the vapor-liquid equilibrium coexistence curve predicting the critical temperature with 5% error. The application of the thermodynamic integration method results in thermodynamic excess quantities as the excess free energy, entropy, and chemical potential. © 2000 American Chemical Society.