Neutral clusters geometry optimization

The Pariser-Parr-Pople Hamiltonian for the description of the 7i-electrons in trans-polyacetylene is reparametrized using ab initio Coupled Cluster Doubles calculations based on a Restricted Hartree Fock reference on trans-butadiene. To avoid the spin contaminations inherent in Unrestricted Hartree Fock (UHF) type calculations on polymethine chains in the doublet state the Annihilated Unrestricted Hartree Fock (AUHF) model is applied in our PPP calculations (tPA (CH) , polyenes H-(CH)2N-H, polymethines H-(CH)2N+1-H). In geometry optimizations on polymethine chains it is shown that in contrast to results from Hiickel type models the width of neutral solitons is strongly... 

TTie vertical electron detachment energy (VDE) is calculated as the total energy difference between the anionic and neutral clusters, both taken in the anionic optimized geometry without die ZPVE. The adiabatic electron affinity (EAa) and ionization energy (lEa) are calculated as the total energy difference between the anionic and cationic clusters, respectively, and the parent neutral cluster in their optimized geometries. 

The question of methanol protonation was revisited by Shah et al. (237, 238), who used first-principles calculations to study the adsorption of methanol in chabazite and sodalite. The computational demands of this technique are such that only the most symmetrical zeolite lattices are accessible at present, but this limitation is sure to change in the future. Pseudopotentials were used to model the core electrons, verified by reproduction of the lattice parameter of a-quartz and the gas-phase geometry of methanol. In chabazite, methanol was found to be adsorbed in the 8-ring channel of the structure. The optimized structure corresponds to the ion-paired complex, previously designated as a saddle point on the basis of cluster calculations. No stable minimum was found corresponding to the neutral complex. Shah et al. (237) concluded that any barrier to protonation is more than compensated for by the electrostatic potential within the 8-ring. 

The optimal ellipsoidal geometries for a given cluster either neutral or charged,... 

The Madelung potential effects were taken into account with Eqs. (6.2) and (6.3). The SCF and modified SCF calculations were carried out at the 6-3IG level, using the in vacuo optimized geometries for the cluster, both in the neutral and ionic forms for the prototype system illustrated by Fig. 3. 

Optimized geometry We begin with the optimized geometry of the ground state of a phenol molecule with clusters of one, three and five ammonia molecules. These are close to the initial geometry of the SET dynamics in the tt—tt state. There are several local minima for the five ammonia case, which are not shown graphically. In contrast to the system with ammonia molecules more than five [265, 457], the phenol is electronically neutral and no charge separation is observed. The proton nucleus, which is later to be shifted to the clusters, is located in the phenol area. 

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