Molecular dynamics simulation of the liquid-vapor interface of dipolar fluids under different electrostatic boundary conditions

Molecular dynamics simulations are performed for a liquid film of strongly and moderate dipolar fluids in equilibrium with its vapor in both, three- a nd two-dimensional (2-D) periodic systems. In the three-dimensional periodi c system, the long-range dipolar interactions are treated by the convention al Ewald summation, where the shape of the basic simulation cell is modifie d in order to study the influence of periodicity on the interfacial propert ies. In the two-dimensional periodic system, an alternative method is used that is based on dividing the 2-D-lattice sum into a lattice sum of the pos ition vectors of the molecules and additional terms describing the dipole o rientations independently of the positions. The results from both technique s agree very well in case that in the 3-D treatment the distance between th e liquid films is sufficiently large. The phase equilibrium data obtained f rom the simulations are verified by a comparison with a recent equation of state. The surface tension results are compared to experimental values usin g the corresponding state principle. Moreover, the orientation of strongly dipolar elongated molecules and Stockmayer molecules at the interface is fo und to be parallel to the interface on the liquid as well as on the vapor s ide. (C) 2001 American Institute of Physics.