Ljubica Andjelković

Treatment of the multimode Jahn-Teller problem in small aromatic radicals.

The family of the Jahn-Teller (JT) active hydrocarbon rings, C(n)H(n) (n = 5-7), was analyzed by the means of multideterminantal density functional theory (DFT) approach. The multimode problem was addressed using the intrinsic distortion path (IDP) method, in which the JT distortion is expressed as a linear combination of all totally symmetric normal modes in the low symmetry minimum energy conformation. Partitioning of the stabilization energy into the various physically meaningful terms arising from Kohn-Sham DFT has been performed to get further chemical insight into the coupling of the nuclear movements and the electron distribution.

Role of spin state and ligand charge in coordination patterns in complexes of 2,6-diacetylpyridinebis(semioxamazide) with 3d-block metal ions: A density functional theory study

We report here a systematic computational study on the effect of the spin state and ligand charge on coordination preferences for a number of 3d-block metal complexes with the 2,6-diacetylpyridinebis(semioxamazide) ligand and its mono- and dianionic analogues. Our calculations show excellent agreement for the geometries compared with the available X-ray structures and clarify some intriguing experimental observations. The absence of a nickel complex in seven-coordination is confirmed here, which is easily explained by inspection of the molecular orbitals that involve the central metal ion. Moreover, we find here that changes in the spin state lead to completely different coordination modes, in contrast to the usual situation that different spin states mainly result in changes in the metal-ligand bond lengths. Both effects result from different occupations of a combination of π- and σ-antibonding and nonbonding orbitals.

Spherical aromaticity of Jahn–Teller active fullerene ions

Density functional theory was applied to compute the nucleus-independent chemical shifts of fullerene (C60), the fullerene ion C6010+, and the Jahn–Teller active fullerene anion C60− and cation C60+. Positioning a 3He nucleus inside the cage of each of these fullerene species facilitates investigations of the substantial differences among them, 3He NMR chemical shifts can provide important data on the aromatic behavior of these molecular cages. Thus, we also calculated the NMR chemical shift of a 3He atom positioned at the center of each fullerene species investigated (C60, C6010+, C60−, and C60+). The data obtained revealed significant differences in the aromatic behavior of the C60 (moderately aromatic) and C6010+ (highly aromatic) species. The values of the nucleus-independent chemical shift parameters were also scanned along the intrinsic distortion path for the C60− and C60+ species. In both cases, antiaromatic character decreases with increasing deviation from high-symmetry structures to low-symmetry global minimum points, resulting in the antiaromatic C60− and weakly aromatic C60+.Graphical Abstract

A simple monomer-based model-Hamiltonian approach to combine excitonic coupling and Jahn-Teller theory

The interplay of excitonic and vibronic coupling in coupled chromophores determines the efficiency of exciton localization vs delocalization, or in other words, coherent excitation energy transfer vs exciton hopping. For the investigation of exciton localization in large coupled dimers, a model Hamiltonian approach is derived, the ingredients of which can all be obtained from monomer ab initio calculations alone avoiding costly ab initio computation of the full dimer. The accuracy and applicability of this model are exemplified for the benzene dimer by rigorous comparison to ab initio results.