A new NICS-based aromaticity index; NICS-rate

The NICS-rate index is introduced as a new aromaticity indicator. The presence of a maximum/minimum in the NICS-rate curve ( Δ NICS Δ r versus r) of a molecule indicates to aromaticity/antiaromaticity of the system. For those molecules, which show both maximum and minimum in their curves, the absolute ratio of the maximum to the minimum NICS-rates (NRR) is defined as a measure of aromaticity. Also NRR = 0.5 is found as the boundary between aromatic and nonaromatic systems. Surprisingly for those molecules in which NICS(0) cannot correctly give the aromaticities of the rings, the NICS-rate successfully predicts the aromaticities of the systems.