Journal
NANOMATERIALS
Volume 10, Issue 6, Pages -Publisher
MDPI
DOI: 10.3390/nano10061236
Keywords
TAO-DFT; electronic properties; graphene nanoflakes; radical nature; strong static correlation
Categories
Funding
- Ministry of Science and Technology of Taiwan [MOST107-2628-M-002-005-MY3]
- National Taiwan University [NTU-CDP-105R7818]
- NCTS of Taiwan
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At the nanoscale, it has been rather troublesome to properly explore the properties associated with electronic systems exhibiting a radical nature using traditional electronic structure methods. Graphene nanoflakes, which are graphene nanostructures of different shapes and sizes, are typical examples. Recently, TAO-DFT (i.e., thermally-assisted-occupation density functional theory) has been formulated to tackle such challenging problems. As a result, we adopt TAO-DFT to explore the electronic properties associated with diamond-shaped graphene nanoflakes withn= 2-15 benzenoid rings fused together at each side, designated asn-pyrenes (as they could be expanded from pyrene). For all thenvalues considered,n-pyrenes are ground-state singlets. With increasing the size ofn-pyrene, the singlet-triplet energy gap, vertical ionization potential, and fundamental gap monotonically decrease, while the vertical electron affinity and symmetrized von Neumann entropy (which is a quantitative measure of radical nature) monotonically increase. Whennincreases, there is a smooth transition from the nonradical character of the smallern-pyrenes to the increasing polyradical nature of the largern-pyrenes. Furthermore, the latter is shown to be related to the increasing concentration of active orbitals on the zigzag edges of the largern-pyrenes.
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