Abstract
Using dipole moments as an example, we study the possibilities of calculating the properties of open-shell systems (radicals) using methods based on the third-order algebraic-diagrammatic construction approximation for the electron propagator and the second-order intermediate state representation formalism (ADC(3)/ISR(2)), designed to treat processes associated with electron detachment and attachment. For the purpose of calculating neutral radicals with an unpaired electron ( \(S = 1{\text{/}}2\) ), the IP and EA variants of the method are applied to the corresponding anion and cation with closed electron shells. This allows calculations to be performed based on the restricted Hartree–Fock method and eliminates problems associated with the use of the unrestricted Hartree–Fock method for open shells in the direct consideration of radicals, such as poor convergence of the iterative process, spin contamination of the wave function, and doubling of the number of molecular orbitals. The dipole moments of the radicals NH \(_{2}^{ \bullet }\) , CN \(^{ \bullet }\) , NO \(_{2}^{ \bullet }\) , OH \(^{ \bullet }\) , HO \(_{2}^{ \bullet }\) , FO \(^{ \bullet }\) , SF \(^{ \bullet }\) , ClO \(^{ \bullet }\) , CH \(^{ \bullet }\) , NO \(^{ \bullet }\) , and PO \(^{ \bullet }\) in their ground states are calculated. The results obtained are in good agreement with the available experimental data.
