Pariser-Parr-Pople parametrization

The last system investigated by the deformation-potential method is a member of the large family of charge-transfer molecular crystals containing as anion the tetracyanoquinodimethane (TCNQ) molecule. The K TCNQ" salt as well as the other TCNQ crystals consist of columns of stacked TCNQ molecules coordinated by similar columns of the cations. The energy band structures of the stack have been calculated earlier with the help of Pariser-Parr-Pople parametrization of the unrestricted Hartree-Fock crystal-orbital method The last two columns of Table 9.10 show that this material behaves again as a normal... 

One example showing a serious discrepancy of the frontier electron method was reported by Dewar H8,ii9). This is 10,9-borazaphenanthrene, and the value of / -B) was reported to have been calculated by the Pople method, but the parameters usyd were not indicated. Fujimoto s calculation by the Pariser-Parr-Pople method 120>, in perfect disagreement with Dewar s, gives the most reactive position as 8, which parallels experiment. The ambiguity involved in the integral values adopted seems to be serious, so that the establishment of parametrization for boron heterocycles is desirable. 

D. The Parametrization of the Pariser-Parr-Pople Approximation for it Electrons. 93... 

The ground-state dipole moments of BPHTs were calculated by evaluating the vector sum of the it moment (computed by the Pariser-Parr-Pople (PPP) method) and the a moment (from cr-bond moments) [17], a separate set of dipole moment values being obtained by the parametric method 3 (PM3) ([25] and references therein) (Table 5). By comparison, the calculated ground-state dipole moment values were considerably lower than the experimental ones. In some cases, the agreement between the experimental and calculated ground-state dipole moments was rather poor [17]. 

The term model Hamiltonian is more general. From this point of view the effective Hamiltonians and pseudo-Hamiltonians could also be considered as model Hamiltonians . However, for clarity, we suggest that the term model Hamiltonian should be used when some simplified form of an approximate Hamiltonian has been guessed from a preliminary physical analysis. In contrast with the effective Hamiltonians and the pseudo-Hamiltonians that can be obtained by means of well defined mathematical procedures, the model Hamiltonians are generally parametrized from experiment. They would involve the semi-empirical Hamiltonians of quantum chemistry and solid-state physics (Hiickel, Hubbard, Pariser-Parr-Pople (PPP),...). 

JJ and Vij are the on-site and intersite Coulomb interactions (note that unlike tij, is not restricted to nearest neighbors and is long range). We use the same % as in Equation 7.20. For the we have chosen a parametrization similar to the Ohno parametrization of the Pariser-Parr-Pople Hamiltonian,... 

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