An analysis of the conformational properties and hydrogen bonding in the condensed phases of glycerol is reported using the same model as adopted in Part I (Phys. Chem. Chem. Phys., 1999, 1, 871). Structural properties of the liquid and glassy states are analyzed in relation to the molecular backbone conformation of the glycerol molecule. The effects of hydrogen bonding and of temperature on the conformational distribution are analyzed. The structural and dynamical properties of hydrogen bonding in glycerol are also investigated. The results are consistent with available experimental observations and clarify many important and interrelated aspects of the microscopic structure of liquid, glassy and crystalline phases of glycerol.

A polarizable electrostatic potential model for classical molecular mechanics is presented. Based on the chemical potential equalization (CPE) principle, the model is developed starting from the original formulation of Mortier, Ghosh, and Shankar [J. Am. Chem. Soc. 108, 4315 (1986)]. Following York and Yang [J. Chem. Phys. 104, 159 (1996)] we present an SP-basis CPE parametrization to describe realistically any sort of molecular system. By fitting ab initio electronic properties, such as dipole moment, polarizability and global molecular hardness of a restricted set of organic molecules, we derive atomic parameters to be applied to a more vast target set of compounds. We show, indeed, that the atomic CPE parameters calculated for the learning set of molecules give reliable values for several electronic properties of various compounds not included in the learning set. The multipole moments obtained by using the proposed CPE parametrization are compared to the results of a fixed charge parametrization like that used by a popular classical molecular mechanics force field, such as AMBER. We show that the fixed charge parametrization can well reproduce only the multipole moments of the molecular conformation or the isomer used for the fit, while being inaccurate when different molecular conformations or isomers are considered. On the contrary, the CPE model realistically reproduces the charge reorganization due to nuclear structural changes of the molecule, such as isomerization or conformational transition. The CPE model has been also tested on various molecular complexes to investigate the polarization response in the case of realistic molecule–molecule interactions. The main result of the paper is the demonstration that the construction of a general polarizable electrostatic force field for classical molecular mechanics is now a viable way.

Using a model potential function we have performed a molecular dynamics simulation of several static and dynamical properties of glycerol in the crystal, glass and liquid phases. Comparison with available experimental data shows an excellent agreeent and proves the validity of the potential model used. For the calculation of the molar specific heat of the liquid and of the glass we have developed a theoretical approach which takes into account the contributions of the conformational structure energy and of the vibrational energy computed using the Bose–Einstein statistics.

In this paper we compare the polarization response given by two different chemical potential equalization schemes to be applied to molecular dynamics simulations: the standard fluctuating point charge model (FQ) and the atom–atom charge transfer model (AACT). We have tested the transferability of FQ and AACT parameters, fitted to the polarizability of small size alkanes and polyenes, to large size homologues. We show that the FQ scheme is not adequate for the n-alkanes as it strongly overestimates the polarizability tensor components as the number of carbon atoms increases. The FQ approach has been found more predictive for highly conjugated systems like polyenes, although still unsatisfactory. The AACT parameters tuned on ethane are instead perfectly transferable to alkanes of any length and conformation. The AACT scheme satisfactorily reproduces the polarization response also for highly conjugated systems.