Application of parametric equations of motion to study uracil anion

When an electron attaches to nucleobases, it forms metastable anion states known as resonances. These occur when the electron occupies the unoccupied π⋆ and σ⋆ orbitals of the base. This article focuses on two main aspects. The first involves an alternative approach to implementing complex absorbing potential in the Fock matrix using parametric equations of motion. The second, and most significant aspect, is the accurate identification of the Lowest Unoccupied Molecular Orbital (LUMO) and the higher energy resonance states, which is achieved through the charge stabilization method, in conjunction with parametric equations of motion. This approach allows for the identification of multiple resonance states using a much larger basis set, which was not possible previously due to the many states with the same symmetry between the Highest Occupied Molecular Orbital (HOMO) and the true LUMO. This method not only overcomes this challenge but also offers significant advantages in computational time. The identified states can be used for post-Hartree-Fock calculations, and in this article, the second-order dilated electron propagator method is applied to account for relaxation and correlation effects.