Efficient first-principles method for calculating the circular dichroism of nanostructures

A first-principles method is developed to study the natural optical activity of nanostructures, making large-scale calculations of electronic circular dichroism feasible. Expressions to calculate circular dichroism using density-functional theory for finite and periodic systems are obtained and implemented within the SIESTA program package. To show the versatility and applicability of the method, the circular dichroism of the high fullerenes C-76 and C-78 is investigated. The results for these fullerenes show good consistency with previous semiempirical calculations, and a very good agreement with experiments. The method is generalized to treat periodic structures such as nanotubes, and the circular dichroism of the carbon single-wall nanotube (4,2) is studied, and the spectrum is interpreted in terms of its electronic density of states. It is found that the calculated circular dichroism spectra can be used to discriminate among different nanostructures through optical activity experiments. It is concluded that this methodology provides theoretical support for the quantification, understanding, and prediction of chirality and its measurement in nanostructures. It is expected that this information would be useful to motivate further experimental studies and the interpretation of natural optical activity in terms of the electronic circular dichroism in nanostructures.