Semi-Empirical Calculations of Energetic Quantities

According to the Mulliken theory of charge transfer complexes, the vertical electron affinity (VEa) of an acceptor and the vertical ionization potential (VIP) of a donor are related to the energy of maximum absorption of the complex (Ect) by the following equation  

Therefore, if a series of complexes are studied in which there is one donor and multiple acceptors, the constants C2 and C can be determined. In order to use this equation, however, there must be experimental values of VEa and VIP. If the data are calibrated to adiabatic values, then Ect is related to AEa for the unknown species. This type of analysis was conducted in 1975 with the data available at the time [33]. 

In 1995 the electron affinities of organic molecules calculated using the standard MINDO/3 or AMI semi-empirical self-consistent field calculations agreed with experiment for molecules containing only CH and O to about 0.1 eV. However, the calculated values differed from experiment for molecules containing N and the halogens by as much as 1 eV. 

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