Force field of monoethanolamine

We have performed ab initio calculations and canonical molecular dynamics simulations to obtain a force field of monoethanolmine (MEA). The molecule is modeled by seven charged sites; and the force field includes intramolecular degrees of freedom and intermolecular interactions. The charges obtained in the energy minimization procedure reproduce the experimental geometry, dipole moment, and the most stable conformation. Molecular dynamics simulations were carried, out in the liquid phase and in the liquid-vapor equilibrium state. Simulations in the liquid region give us information about hydrogen bond formation, while simulations in the two-phase region allow us to obtain the coexisting densities and surface tension as functions of temperature. The hydrogen bond is favored when the hydrogen of the hydroxyl group is close to a nitrogen or to an oxygen of another molecule, and the strength in both cases is the same. Radial distribution functions involving hydrogens and oxygen in the hydroxyl group of MEA ate compared with those of water at 298 K, and a similar structure is found for die first neighbor of atoms. The proposed force field gives a good description of the liquid-vapor coexistence of MEA. The liquid density obtained in our simulations of the;liquid-vapor equilibrium at 298 K is 1.003 g/cm(3) Versus the experimental value of 1.012 g/cm(3). Our estimated critical point is located at 583.9 K and 0.32 g/cm(3) in comparison with the experimental result of 614 K and 0.3116 g/cm(3), respectively. At 323 K the calculated surface tension is 43.2 +/- 2.5 mN/m while the experimental value is 44.81 mN/m.