Generalized Perturbative Singles Correction to the Random Phase Approximation Method: From Intermolecular Interactions in Open-Shell Systems to Surface Adsorption

The post-Kohn–Sham (KS) random phase approximation (RPA) method may provide a poor description of interaction energies of weakly bonded molecules due to inherent density errors in approximate KS functionals. To overcome these errors, we develop a generalized formalism to incorporate perturbative singles (pS) corrections to the RPA method using orbital rotations as a perturbation parameter. The pS schemes differ in the choice of orbital-rotation gradient and Hessian. We propose a pS scheme termed RPA singles (RPAS) that uses the RPA orbital-rotation gradient and the Hartree-Fock Hessian. This correction reduces the errors in noncovalent interaction energies of closed- and open-shell dimers. For the open-shell dimers, the RPAS method leads to a consistent error reduction by 50% or more compared to the RPA method for the cases of hydrogen-bonding, metal–solvent, carbene–solvent, and dispersion interactions. Similarly, the RPAS correction reduces the underbinding observed in RPA for molecule-surface interaction in ionic materials, leading to chemical accuracy and correct description of interaction energy ordering of small molecules with Mg(001). The consistent improvements obtained using RPAS method highlight its importance as a reliable beyond-RPA correction.