QUANTUM DELOCALIZATION OF NUCLEI AND ELECTRONS - CYCLOBUTADIENE

A Feynman path integral method for evaluating the quantum delocalizati on of atomic nuclei is combined with a scheme for calculating electron ic delocalization parameters in the correlated electronic ground state . As model system we have selected the cyclobutadiene molecule whose p i-electronic structure is discussed in the Pariser-Parr-Pople and Hubb ard approaches. The dynamics of the electrons are described by the cha rge fluctuations as well as by the probabilities P(n) of finding n = 0 , 1,2 pi-electrons at the respective atomic site. For both Hamiltonian s we have compared the pi-electron delocalization properties in the fe rmionic state \psi(fe)] with those realized in the so-called hard core bosonic state \psi(hcb)]. The negative sign in \psi(fe)] leads to a s uppression of the charge fluctuations in comparison to their \psi(hcb) ] value. The dynamics of the electrons are attenuated by the quantum d elocalization of the atomic nuclei. Details of this overall effect dep end both on the nature of the pi-Hamiltonian and on the nature of the electronic wavefunction.