Molecular dynamics simulation of biphenyl dissolved in a liquid crystalline solvent: A test of theoretical methods of deriving rotational potentials from partially averaged nuclear spin dipolar couplings

A molecular dynamics simulation has been carried out of biphenyl dissolved in a solvent comprised of rigid particles interacting with the Gay-Berne potential, The solution is investigated in isotropic, nematic, and smectic phases, and the probability distribution, P-LC(phi) obtained, where phi is the angle between the two ring normals. This is compared with P-mol(phi), the distribution calculated for an isolated molecule, and it is found that the positions, phi(max) of the maxima of the two distributions differ by about 2 degrees, The molecular dynamics trajectory is used to calculate averaged nuclear spin dipolar couplings, D-ij, and these are used to test the maximum entropy (ME) and additive potential (AP) theoretical models which have been used previously to obtain the distribution P-LC(phi) from dipolar couplings obtained on real solutions of biphenyl in liquid crystalline solvents. It is concluded that the AP method is able to recover the true distribution PLC(St) from the simulated D-ij with good precision at all the temperatures studied, whereas the ME method achieves good precision only when the orientational order is high. The AP method also succeeds in obtaining the correct difference between P-LC(phi) and P-iso(phi), the distribution for an isotropic phase at the same temperature. (C) 1996 American Institute of Physics.