A comparative study of the equations of motion, and configuration interaction methods for the calculation of excitation properties of methane and water

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Abstract
In this paper we provide a direct comparison (over the same molecular basis) of the Equations of Motion (EOM) method and Configuration Internation (CI) methods, for the calculation of excitation properties of water and methane. We find that when double particle-hole interactions have been included in the EOM method and double excitations in the CI method, the results from the EOM method are in closer agreement with the experimental values than the results from the CI method. Furthermore, we find the EOM method to be more economical and convenient, from a computational point of view, than the corresponding CI method. The results from the EOM method also tend to be less sensitive to the choice of basis set than the results from the usual CI treatment.