Project R-5957

Quantum chemical study of large polycyclic aromatic hydrocarbons and graphene nanoislands using Density Functional Theory with fractional orbital occupations (Research)

The first purpose of this project is to contribute to the development of a new approach referred to as Thermally Assisted Occupation Density Functional Theory (TAO-DFT), which has been especially designed for treating on spin-consistent grounds static electron correlation in large and strongly correlated systems. The effective temperature governing the Fermi-Dirac distribution of orbital occupations in TAO-DFT will be properly parameterized in function of DFT estimates of the fundamental or optical band gaps, through systematic comparisons with the results of multi-reference calculations on model chains of hydrogen or berrylium atoms, n-acenes and small polycyclic aromatic hydrocarbons (PAHs). The TAO-DFT approach will then be used to investigate the non-magnetic and magnetic states of large PAHs and graphene nanoislands, as well as their behavior in the presence of an external electric field. We will thereby elucidate the origin of magnetism in nanographite domains and assess whether large zig-zag edged graphene nanoribbons can exhibit genuine half-metallicity, in the absence of external magnetic fields or structural defects such as vacancies, adatoms, curvatures, or Stone-Wales defects, and taking care of the increasing influence of the basis set with increasing system size, as well as complications due to spin-orbit couplings and near-energy degeneracies resulting in artefactual symmetry-breakings of spin-densities in spin-unrestricted DFT studies of singlet states.

01 January 2015 - 31 December 2018