Classifying variational functions for quasi-one-dimensional systems and incorporating electron correlation

A classification is proposed for the variation functions in the variable localized geminals (VLG) approximation based on the types of variational function in the unrestricted Hartree-Fock (UHF) method for one-dimensional systems. It has been found that functions of VLG type provide better incorporation of electron-correlation effects than do UHF ones. A study has been made on the phase diagram for the electronic states of polyacetylene in relation to the electron-electron parameters in the extended Hubbard Hamiltonian containing certain types of VLG function