Electrostatic potentials and Mulliken net atomic charges were calculated from STO-3G, 6-31G, and 6-31G* * SCF-MO wavefunctions for hydrogen fluoride, water, ammonia, methane, acetylene, ethylene, carbon dioxide, formaldehyde, methanol, formamide, formic acid, acetonitrile, diborane, and carbonate ion. In each case optimized net atomic charges (potential-derived charges) were also obtained by fitting the electrostatic potentials calculated directly from the wavefunctions in a shell enveloping the molecules outside of their van der Waals surfaces. The electrostatic potentials calculated from the potential-derived charge distributions were then compared with the defined quantum mechanical electrostatic potentials and with the electrostatic potentials of the Mulliken charge distributions.
Inclusion of polar organic molecules in molecular sieve hosts has been investigated as a means of creating self-assembled aggregates of molecules that possess the noncentrosymmetry required for materials to exhibit second harmonic generation (SHG). Aluminophosphate molecular sieves with one-dimensional channel structures are shown by SHG powder measurements to successfully direct this self-aggregation for a number of organic molecules including and related to p-nitroaniline. Models supported by FTIR evidence show the aggregates could be chains of molecules with a large net dipole that form within the molecular sieve channels. The polar host crystal then aligns the aggregates to produce a large bulk dipole moment and the observed SHG signal. Three methods for controlling the SHG intensity within a particular host structure have been elucidated: (1) variation of guest concentration, (2) alteration of guest structure, and (3) changing the charge density on the host framework.
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