Dear friend,

The algorithm may be useful:

1. Choose a method, possibly DFT

2. Calculate the optimized geometry of the neutral molecule (see the Opt keyword in the Gaussian manual) for E_0

3. Calculate the vertical transition energy for an optimized geometry from (2) using the TD-DFT method and find the E_00 of the required transition.

3. Set the ion charge (±) and, using the optimized geometry from (2), calculate (without optimization) the single point energy E_0^±

4. Calculate the optimized cation/anion geometry (±) to obtain E_±^±

5. Set the charge (0) and, using the optimized cation/anion geometry from (4), calculate (without optimization) the single point energy E_±^0

6. Calculate lambda_i by the formula