Density functional theory calculation of electronic circular dichroism using London orbitals

We present the first implementation of gauge-origin independent electronic circular dichroism (ECD) at the density functional theory level in the length-gauge formulation, where gauge origin independence has been ensured through the use of London atomic orbitals. We investigate the dependence of the rotatory strengths on the choice of gauge formulation, the size of the basis set, and on the choice of density functional for several selected small molecules. The ECD parameters are also calculated for a few larger molecules, and the results are compared with experiment where available, as well as with previously published theoretical numbers. Using the length-gauge formulation instead of the velocity-gauge gives in general better basis set convergence. However, large basis sets are still needed in order to get reliable ECD results, and a double set of diffuse functions are in general required.