Wave Functions and Energy Eigenvalues for the Polytetrafluoroethylene Chain

Abstract

The paper reports on a quantum mechanical investigation of an isolated polytetrafluoroethylene molecule. The purpose of this investigation is twofold: to find the energy gap between filled and empty electronic bands and to determine the energy required to change the conformation of the molecule. For reasons of simplicity, the carbon atoms are assumed to have the planar zigzag conformation in the ground state of the molecule. Molecular wave functions are constructed from Bloch sums taken along the four rows of fluorine atoms. The basis functions used are Gaussian approximations to 2p and 3s atomic orbitals. The suitability of this choice is tested in a preliminary calculation of the dissociation energy of the hydrogen fluoride molecule. In polytetrafluoroethylene, the molecular orbitals form bands. The energy gap between the filled 2p band and the empty 3s band is calculated as 10.07 ev, suggesting negligible intrinsic semiconduction. The width of the 2p band is 0.0625 ev, signifying that chain conformation may change easily at room temperature, for example from a right-handed helical conformation to the conformation of the opposite hand.