Charge vs. spin density waves in the fullerene polymer

Abstract

Using an effective model Hamiltonian, we performed bond-length-optimized RHF and UHF band structure calculations to describe the electronic structure of the fullerene Ž . polymer C . For the doped system, the RHF calculations predict a gap on the 100 60 x meV scale, in good agreement with experimental data, and show a special kind of charge-density-wave solution. At certain geometries, when the intercage conjugation is hindered, the RHF calculations are triplet instable: A carefully chosen initial guess to UHF leads to a small-amplitude spin-density-wave solution.

Improved description of the orbital relaxation effect by practical use of the self‐energy

“…Here, we examine the correction by the self-energy shifting, [21,22] by considering several molecules, formaldehyde, water, and 2,3,5,6-tetrafluorobenzene, for which the results are shown in Table 5. For formaldehyde, a typical test case for comparison of the Rydberg and valence excitations, as presented in Ref.…”

“…To overcome this drawback, an optimal damping parameter is introduced into the OR term in combination with the scaled-opposite spin parameterization for the CIS(D) model. [20] Another procedure to compensate this situation is Dyson-shifting, [21,22] which is also known as the self-energy shifting [23,24] in the OR term, in combination with the damping parameter. By shifting the denominator of the OR term with the correlated self-energy, the higher-order effects are effectively introduced without a drastic increase in the computational effort.…”