sp-hybridized carbon allotrope molecular structures: An ongoing challenge for density-functional approximations.

Area of Science:

• Computational Chemistry
• Materials Science
• Organic Chemistry

Background:

• A novel C18 monocyclic ring, an all-carbon allotrope, has been synthesized.
• Existing density functional theory (DFT) methods inaccurately predict its structure, favoring a cumulenic form over the experimental polyynic structure.

Purpose of the Study:

• To address the failure of modern DFT approaches in correctly predicting the polyynic structure of the C18 monocyclic ring.
• To identify computational schemes capable of accurately describing this new all-carbon material.

Main Methods:

• Application of recently developed range-separated nonempirical schemes.
• Testing the performance of these schemes across various functional types (semilocal, hybrid, double-hybrid).

Main Results:

• The developed range-separated nonempirical schemes successfully resolved the structural prediction discrepancy.
• Accurate prediction of the polyynic structure was achieved irrespective of the specific functional used.

Conclusions:

• Range-separated nonempirical schemes offer a robust solution for accurately modeling the electronic structure of novel all-carbon materials.
• These advanced computational methods overcome significant limitations of standard DFT for complex carbon allotropes.