Application of electronic structure methods to coupled Drude oscillators

• Published in: Chemical physics letters 2015-06, Vol.630, p.76-79
• Main Authors: Odbadrakh, T.T., Voora, V., Jordan, K.D.
• Format: Article
• Language: English
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/j.cplett.2015.04.031

•The interaction of Drude oscillators is calculated using RPA and CI methods.•Configuration interaction requires an infinite dimension matrix for exact solution.•RPA recovers exact solution with the smallest possible excitation space.•Past 2nd order, RPA energy is dominated by exclusion-principle-violating diagrams. The configuration interaction, perturbation theory, coupled cluster doubles, and random phase approximation methods are applied to a system of two quantum Drude oscillators interacting through dipole–dipole coupling. It is found that the random phase approximation gives the exact excitation energies and exact interaction energy of this system even when allowing only excitations into the first excited levels of the oscillators. In contrast, to obtain the exact results from configuration interaction or coupled cluster treatments of the model requires inclusion of excitations into all accessible excited configurations.