Polarizable intermolecular potential functions

Gao JL, Habibollazadeh D, Shao L (1995) A polarizable intermolecular potential function for simulation of liquid alcohols. J Phys Chem 99(44) 16460-16467... 

Gao JL, Pavelites JJ, Habibollazadeh D (1996) Simulation of liquid amides using a polarizable intermolecular potential function. J Phys Chem 100(7) 2689-2697... 

Xie WS, Pu JZ, MacKerell AD, Gao JL (2007) Development of a polarizable intermolecular potential function (PIPF) for liquid amides and alkanes. J Chem Theory Comput 3(6) 1878-1889... 

J. Gao, D. Habibollahzadeh and L. Shao, A Polarizable Intermolecular Potential Function for Simulation of Liquid Alcohols, J. Phys. Chem. 99 (1995) 16460. 

In this expression, the dipole dipole interactions are included in the electrostatic term rather than in the van der Waals interactions as in Eq. (9.43). Of the four contributions, the electrostatic energy can be derived directly from the charge distribution. As discussed in section 9.2, information on the nonelectrostatic terms can be deduced indirectly from the charge density. The polarizability a, which occurs in the expressions for the Debye and dispersion terms of Eqs. (9.41) and (9.42), can be expressed as a functional of the density (Matsuzawa and Dixon 1994), and also obtained from the quadrupole moments of the experimental charge density distribution (see section 12.3.2). However, most frequently, empirical atom-atom pair potential functions like Eqs. (9.45) and (9.46) are used in the calculation of the nonelectrostatic contributions to the intermolecular interactions. 

Luo237 has attempted to establish a power law for scaling the static y-hyperpolarizabilites of the fullerenes as a function of the number of carbon atoms. C6o does not fit into the relationship, a result attributed to its exceptional electron localization. An intermolecular potential model of with distributed dipole interactions has been used by Gamba238 to obtain the polarizability and multipole moments. Measurements of the third order response of fullerenes in CS2 have been reported by Huang et al.239 and correlated with chemical structure. 

A useful alternative approach is to isolate the components of the perturbation expansion, namely the repulsion, electrostatic interaction, induction, and dispersion terms, and to calculate each of them independently by the most appropriate technique. Thus the electrostatic interaction can be calculated accurately from distributed multipole descriptions of the individual molecules, while the induction and dispersion contributions may be derived from molecular polarizabilities. This approach has the advantage that the properties of the monomers have to be calculated only once, after which the interactions may be evaluated easily and efficiently at as many dimer geometries as required. The repulsion is not so amenable, but it can be fitted by suitable analytic functions much more satisfactorily than the complete potential. The result is a model of the intermolecular potential that is capable of describing properties to a high level of accuracy. 

Taking the Intermolecular potential in a liquid as decomposable into a sum of a repulsive potential depending only on nuclear coordinates and the Coulomb potential between the electronic and nuclear charges of different molecules, the latter taken as a perturbation to a classical liquid with a purely repulsive Intermolecular potential, one can perform a quantum perturbation expansion of the trace of the statistical operator exp(- H) and similarly expansions of the thermally averaged, imaginary time displaced, molecular charge correlation functions pO, t )>. The individual terms in the expansions consist of multipolar interaction tensors and functionals of molecular polarizabilities of various orders. Summation of all terms depending only on linear molecular polarizabilities lead to ... 

Theory. If the invariants of the pair polarizability are known, along with a refined model of the intermolecular interaction potential, the lineshapes of binary spectra can be computed quite rigorously [227, 231, 271], Lineshape computations based on exact or approximate classical trajectories are known [196, 264, 276, 316, 337]. Such computations generate spectral functions that are symmetric, g — co) = g((o). For massive pairs at high enough temperatures, such classical profiles are often sufficient at frequency shifts much smaller than the average thermal energy, ha> < kT, albeit special precaution is necessary when the system forms van der Waals dimers [302]. 

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