Basic Assumptions of Pariser-Parr-Pople Theory

Basic Assumptions of the Pariser-Parr-Pople Theory 

The nuclear charges and the y electrons form a fixed charge distribution, the so-called core, which is not affected by any change in the sr-electron distribution. The singlet ground state wave function therefore describes only the n system and is given by a single closed-shell Slater determinant Aq which is constructed from a set of 5r-molecular spin orbitals (SMO) ( la), ( 2 ). etc. 

Every occupied molecular orbital (MO) is taken with and spin and if there is symmetry degeneracy the whole degenerate set is included. 

The MO s (i) are approximated by a linear combination (LCAO) of basis function Xn i) (ju = l.. . B), which can be thought of as 2-pi functions centered at all the B atoms that contribute n electrons to the n system. 

It is assumed that the basic functions have zero differential overlap (ZDO)  

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