Atomistic simulation of a nematogen using a force field derived from quantum chemical calculations

Bulk phase atomistic computer simulations of 4-n-pentyl-4'-cyanobiphenyl (5CB) were performed with a specific force field obtained from ab initio and DFT calculations. The intermolecular potential was previously derived through the fragmentation reconstruction method (FRM), developed in our group. The description of some intramolecular interactions, like the torsional potential between the phenyl rings and at the aryl-alkyl linkage, is achieved through accurate DFT studies. Lengthy ( approximately 40 ns) molecular dynamics (MD) simulations were then carried out at constant atmospheric pressure and different temperatures. The system was stable in the experimental crystalline structure up to 285 K, where the early stage of the melting process appears with the loss of positional order. At higher temperatures (between 290 and 305 K) a kinetically stable, orientationally ordered phase is obtained. This nematic phase was reached starting with three initial configurations, differing in their orientational order parameter. The calculated values of thermodynamic and structural properties of each phase were in fairly good agreement with the relevant experimental data.