The Generalized Hückel Rule – Electronic Structure of Carbon Nanocones

Work package:
We recently investigated a particular class of carbon nanocones [1], and presented a generalized Hückel rule that predicts the character of their ground state based on simply the three topological indices that uniquely define them [2]. Importantly, this rule applies to both flat and curved systems, encompassing a wide variety of known structures that do not satisfy the ``classic'' 4n+2 rule, such as Coronene, Corannulene and Kekulene. This rule was tested at the Hückel level of theory for a large number of systems, including structures that are convex, flat and with a saddle-like geometry, and at the CASSCF level for a selected representative subset of molecules. During this internship, we plan to investigate a series of structures that present a symmetry axis of order four, and are often characterized by an open-shell wave-function. In such a case, the use of multi-reference ab-initio methods is particularly recommended. For this reason, the investigation will be performed in particular at CAS-SCF and NEVPT-2 levels, by using the MOLPRO quantumchemistry package.