Helical Organic and Inorganic Polymers

Abstract

Despite being a staple of synthetic plastics and biomolecules, helical polymers are scarcely studied with Gaussianbasis-set ab initio electron-correlated methods on an equal footing with molecules. This article introduces an ab initio second-order many-body Green's function [MBGF(2)] method with nondiagonal, frequency-dependent Dyson self-energy for infinite helical polymers using screw-axis-symmetry-adapted Gaussianspherical-harmonics basis functions. Together with the Gaussianbasis-set density-functional theory for energies, analytical atomic forces, translational-period force, and helical-angle force, it can compute correlated energy, quasiparticle energy bands, structures, and vibrational frequencies of an infinite helical polymer, which smoothly converge at the corresponding oligomer results. These methods can handle incommensurable structures, which have an infinite translational period and are hard to characterize by any other method, just as efficiently as commensurable structures. We apply them to polyethylene (2/1 helix), polyacetylene (Peierls' system) and polytetrafluoroethylene (13/6 helix) to establish the quantitative accuracy of MBGF(2)/cc-pVDZ in simulating their (angle-resolved) ultraviolet photoelectron spectra and of B3LYP/cc-pVDZ or 6-31G** in reproducing their structures, infrared and Raman band positions, phonon dispersions, and (coherent and incoherent) inelastic neutron scattering spectra. We then predict the same properties for infinitely catenated chains of nitrogen or oxygen and discuss their possible metastable existence under ambient conditions. They include planar zigzag polyazene (N 2 ) x (Peierls' system), 11/3-helical isotactic polyazane (NH) x , 9/4-helical isotactic polyfluoroazane (NF) x , and 7/2-helical polyoxane (O) x as potential high-energy-density materials.

MQM 2022: The 10th Triennial Conference on Molecular Quantum Mechanics

“…They report that such errors may be reduced by including generalized cusp conditions in the wave function representation for small electron–electron distances. Finally, in the only MQM VSI contribution appearing in the Journal of Physical Chemistry B , Hirata of the University of Illinois, Shigeta of University of Tsukuba, Xantheas of Pacific Northwest National Laboratory, and Bartlett of the Quantum Theory Project at the University of Florida introduce an ab initio second-order many-body Green’s function method for infinite helical polymers . Their approach allows for the calculation of a wide range of properties of such species, and they apply it to a set of paradigmatic polymers for which they compute structures, infrared and Raman frequencies, phonon dispersions, and inelastic neutron scattering spectra.…”