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The van der Waals coefficients between carbon nanostructures and small molecules: A time-dependent density functional
C Kamal1, T K Ghanty, Arup Banerjee
1Semiconductor Laser Section, Raja Ramanna Centre for Advanced Technology, Indore 452013, India.
The Journal of Chemical Physics
|November 10, 2009
Summary
This study quantifies van der Waals (vdW) interactions using C(6) coefficients for carbon nanostructures. Longer nanotubes exhibit stronger vdW forces, while cages are less interactive than nanotubes.
Area of Science:
- Computational Chemistry
- Materials Science
- Condensed Matter Physics
Background:
- Accurate calculation of long-range van der Waals (vdW) interactions is crucial for understanding molecular and material properties.
- Dispersion coefficients, specifically C(6), quantify the strength of these vdW forces.
- Carbon nanostructures like fullerenes and carbon nanotubes exhibit significant vdW interactions with other molecules.
Purpose of the Study:
- To calculate and compare the long-range dipole-dipole dispersion coefficients (C(6)) for fullerenes and finite-length carbon nanotubes.
- To investigate the influence of shape and size on vdW interaction strengths.
- To determine C(6) values for interactions between carbon nanostructures and various small molecules.
Main Methods:
- Employed an all-electron ab initio time-dependent density functional theory (TD-DFT) based method.
- Calculated C(6) coefficients using the Casimir-Polder relation.
- Utilized an asymptotically correct exchange-correlation potential (statistical average of orbital potential).
Main Results:
- Carbon nanotube C(6) coefficients increase nonlinearly with length, indicating stronger vdW interactions for longer nanostructures.
- Carbon cages show 40%-50% lower C(6) values and polarizability compared to quasi-one-dimensional nanotubes of similar atomic content.
- H(2) exhibits a significantly larger C(6) value with carbon nanostructures than He; environmentally relevant molecules and halogenated compounds (e.g., CCl4, Cl2) show high C(6) values due to high polarizability.
Conclusions:
- The length of carbon nanotubes strongly influences the magnitude of vdW interactions.
- Carbon cages are less prone to vdW interactions than carbon nanotubes.
- The polarizability of small molecules dictates the strength of their vdW interactions with carbon nanostructures, with halogenated compounds being particularly interactive.
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