Multicenter multipole models

Many investigations of azabenzenes have used multicenter multipole models. This type of model is discussed in the next section. The use of a point dipole at nitrogen is especially popular. Price and Stone " carried out a multipole analysis through atomic quadrupoles. At long distance the use of point... 

Recently, Sokalski et al. presented distributed point charge models (PCM) for some small molecules, which were derived from cumulative atomic multipole moments (CAM Ms) or from cumulative multicenter multipole moments (CMMMs) [89,90] (see Sect. 3.2). For this method the starting point can be any atomic charge system. In their procedure only analytical formulas are used,... 

The electric potential resulting from any charge distribution can be represented by a convergent multicenter multipole expansion.Molecular moments of isolated molecules can be obtained experimentally, such as from the Stark effect on the microwave spectra of gas molecules. Studies of van der Waals clusters and molecular association in general require a multicenter model for short-range electrostatic interaction. Mulder and Huiszoon, for instance, found that a molecular multipole expansion was not satisfactory for the electrostatic interaction of... 

Very simple models are often used for water and other small polar molecules, with a single LJ site and a few charge sites whose size and location is optimized to reproduce the first multipoles, usually dipole and quadrupole. Accurate multicenter expansion would require higher order multipoles, in addition to point charges [9] (note that the distribution of multipoles is not unique [1,29,30,33-37]). 

---