AN LDA CALCULATION OF THE CONFORMATION AND ELECTRONIC-STRUCTURE OF POLYTETRAFLUOROETHYLENE

A density functional calculation of the structural and electronic prop erties of polytetrafluoroethylene systems with several different dihed ral angles is presented using two different local density approximatio ns, the Gaspar-Kohn-Sham and the Perdew-Zunger. All the geometrical pa rameters were optimized simultaneously for the stable conformation. Th e torsional potential curve shows an absolute minimum at the dihedral angle of 163.7 degrees, corresponding to a slightly deformed planar zi gzag conformation. Other two distinct local minima for the quasi-stabl e helical conformation are found at the gauche form. The calculated va lence and conduction bands are discussed and compared with other theor etical calculations and experiment. (C) 1997 John Wiley & Sons, Inc.