Single Reference Treatment of Strongly Correlated H₄ and H₁₀ Isomers with Richardson-Gaudin States

Richardson-Gaudin (RG) states are employed as a variational wave function ansatz for strongly correlated isomers of H-4 and H-10. In each case, a single RG state describes the seniority-zero sector quite well. Simple natural orbital functionals offer a cheap and reasonable approximation of the outstanding weak correlation in the seniority-zero sector, while systematic improvement is achieved by performing a configuration interaction in terms of RG states.