INDO/X: A New Semiempirical Method for Excited States of Organic and Biological Molecules.

The semiempirical method INDO/S is a well-known computational tool for calculating spectroscopic properties of molecular systems. This scheme has been modified and reparameterized using the TBE-2 benchmark excitation energies and oscillator strengths. The developed method referred to as INDO/X provides significant improvements over INDO/S. The mean absolute deviations of the INDO/X excitation energies relative to the TBE-2 data is 0.26 eV for singlet states and 0.33 eV for triplet states. The corresponding values for INDO/S are 0.56 and 0.64 eV. Also, the oscillator strengths estimated with INDO/X are in good agreement with the benchmark data. The proposed method is very fast and may be applied to large organic and biological molecules.