Local density approximation calculation of the conformation and electronicstructure of poly(fluoroethylene)s

A series of density functional calculations of the structural and electroni c properties of all six different fluorinated polyethylenes with several di fferent dihedral angles are performed using two different local density app roximations (LDA's), the Gaspar-Kohn-Sham and the Perdew-Zunger ones. The g eometrical parameters are optimized simultaneously for the stable conformat ion of poly(tetrafluoroethylene) and poly(difluoroethylene). The torsional potential curves for all the poly(fluoroethylene)s show an absolute minimum at dihedral angles other than 180 degrees, corresponding to a nonplanar co nformation. For poly(difluoroethylene), the absolute minimum is found at th e gauche form. The valence and conduction bands as well as the Mulliken pop ulations are calculated and compared with other theoretical calculations an d experimental results.