Thermodynamics of self-assembled molecular layers of trimesic acid from fields-supported kinetic Monte Carlo simulation.

In this study we present a thermodynamic analysis of several self-assembled molecular layers of trimesic acid (TMA), gas-solid and solid-solid transitions in such layers using the recently proposed Field(s)-supported MultiPhase kinetic Monte Carlo (FsMP/kMC) method. Simulations were performed in an elongated cell comprising a gas-crystal system under an external potential and a damping field imposed on the gas phase and the interphase. The damping field diminishes the intermolecular potentials, which makes it possible to increase the gas phase density by several orders of magnitude. In turn, this provides reliable determination of the chemical potential of the entire system, including the crystal. The effect of temperature and density on entropy and other thermodynamic functions has been thoroughly investigated. At higher temperatures the chicken-wire (CW) structure with the lowest density is the most stable phase. We revealed a phase transition from the close-packed to CW structure at 435 K. Further increase in temperature leads to disassembling CW structure without the appearance of a liquid-like phase. Thermodynamic analysis of the gas phase showed that the critical temperature of the gas is lower than the disassembling temperature. Although the damping field acts like an increase in temperature along the same system, the thermodynamic equilibrium condition is not violated, which is confirmed by the Gibbs-Duhem equation. This makes the FsMP/kMC method a potentially universal tool for the thermodynamic analysis of crystals formed by "heavy" molecules of any complexity.