Conformations of 2,4-Diphenylpentane:  A Quantum Chemistry and Gas-Phase Molecular Dynamics Simulation Study

Abstract

We report on the relative conformer energies and rotational energy barriers for meso and racemic 2,4-diphenylpentane (DPP) from ab initio electronic structure calculations. It is found that dispersion interactions between phenyl rings strongly influence the conformational geometries, necessitating the inclusion of electron correlation in both geometry optimizations and energy calculations. Furthermore, basis set superposition contributions to the phenyl-phenyl interactions, estimated by extracting the phenyl rings from the optimized DPP geometries and computing the basis set superposition error for the resulting benzene dimer configurations, are significant. An atomistic molecular mechanics force field is parametrized to reproduce our best values for the conformational energies and rotational energy barriers in DPP obtained from ab initio calculations. Conformational energy contour maps are presented for the DPP enantiomers, and their salient features are discussed. Gas-phase molecular dynamics simulations of DPP have been performed using the quantum chemistry based force field. Important entropic contributions to the conformer populations, due primarily to restricted phenyl group rotation, are discussed.

Interface characteristics of polystyrene melts in free-standing thin films and on graphite surface from molecular dynamics simulations

“…The first is the potential inaccuracy of the force field. As mentioned above, Smith et al's force field [53] employed in the present study describes the bulk states very well; however, the surface tension is very sensitive to the interactions among the small number of molecules in the surfaces. Thus, for a precise calculation, the force field should describe very accurately the vapor phase as well as the liquid phase.…”

“…In doing so, we first performed NPT MD simulations (fixed number of particles, pressure, and temperature) for a cubic simulation box with periodic boundary conditions in all directions [ Figure 1(a)]. After the bulk phase was fully equilibrated by monitoring the density and chain conformations [40,49,55], the simulation box was elongated along the z -direction by about 3 to 4 times without scaling the coordinates of atoms, which subsequently generates free surfaces at both sides ( We used the explicit-atom force field of Smith et al [53] for the intermolecular and intramolecular interactions of PS chains. From the bulk simulations, we obtained the density at 450 K of 0.984 g/cm 3 .…”

“…In the present work, we performed molecular dynamics (MD) simulations of polystyrene (PS) melts in free-standing thin films and on a graphite substrate using an explicit all-atom model [53]. Our choice of PS films was motivated, firstly, by the experimental observations that among all the polymers investigated so far, PS films exhibit the most pronounced depression of T g in thin films and the thickest mobile layer in the free-surface region in the temperature range below the T g of the bulk sample [6,54].…”

Gas-phase conformations and exciton couplings in 5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene

“…However, the MP2 method often overestimates conjugation [14], which might lead to overestimation of the relative stability of the TB conformer in which dispersive interactions between the p electron clouds are possible. Smith et al [15] reported that better relative energies of the various configurations of the benzene dimer (where dispersive interactions play an important role in determining the relative stability of the various configurations of the dimer) are obtained by performing single point MP2 energy calculations on HF optimized geometries. The results of this work also reveal that the single point MP2 relative energies on HF optimized geometries of THDC conformers are in excellent agreement with the experimental relative conformational energies (vide infra).…”

Sorption Mechanism of Aromatic Molecules in the Interface between Liquid and Polymer Crystal

“…The potential parameters were taken from the all-atom force field, AMBER [18]. The weak partial charges were assigned only to the aromatic hydrogen (þ 0.085e) and aromatic carbon which is bonded to the hydrogen (2 0.085e), following the ab initio calculation of Smith et al [19]. The potential parameters of the noble gases were taken from the literature [20].…”