CCSD calculations on C(14), C(18), and C(22) carbon clusters

Area of Science:

• Computational Chemistry
• Materials Science
• Nanotechnology

Background:

• Carbon clusters exhibit diverse structures and energetics.
• Previous studies showed discrepancies in predicting stable isomers for C(4n+2) systems.
• Understanding these structures is crucial for designing novel carbon-based materials.

Purpose of the Study:

• To accurately determine the ground-state structures and energetics of C(4n+2) carbon rings (n=3-5).
• To resolve discrepancies in literature regarding the isomeric forms of these carbon clusters.
• To investigate the role of Peierls distortion in C(4n+2) ring systems.

Main Methods:

• Coupled-cluster singles and doubles (CCSD) excitation theory was employed for high-accuracy electronic structure calculations.
• Density functional theory (DFT) was used for comparative analysis.
• Analysis of bond lengths, bond angles, and symmetry was performed to characterize isomers.

Main Results:

• C(14), C(18), and C(22) carbon rings favor bond-length and bond-angle alternated acetylenic structures.
• CCSD calculations identified D((2n+1)h) cumulenic structures as lowest energy for C(14) and C(18), and C((2n+1)h) acetylenic for larger clusters.
• Peierls-type distortion was observed at C(14), indicating a structural transition.

Conclusions:

• CCSD theory provides a more accurate description of C(4n+2) carbon ring structures than DFT.
• The transition from cumulenic to acetylenic structures is driven by Peierls distortion starting at C(14).
• These findings offer insights into the fundamental properties of carbon nanomaterials.