Ab initio study of the lower few states of FeH: Application of the multireference coupled pair approximation

A fourth-order approximation of MRCPA theory, MRCPA(4), was applied to low-lying states of FeH. Overall, MRCPA(4) provided proper relative stability between X4Δ and a6Δ, for which it has long been difficult to make a theoretical prediction. Results of this study will be helpful in interpreting a system with complicated experimental data.