CCSD(T) calculations of the electron affinity of the uracil molecule

The adiabatic electron affinity (AEA) and the vertical detachment energy (VDE) of the π∗ valence-type uracil anion is calculated by the ROHF CCSD(T) method using the optimized virtual orbital space (OVOS). Truncation of the original space of virtual orbitals allows calculations of the uracil anion with basis sets up to aug-cc-pVQZ, which would be prohibitively demanding by using traditional methods. Spin adaptation of the CC amplitudes reduces AEA by 30 meV. Our results indicate that the extra electron is unbound to the uracil molecule by 15 meV.