• TDDFT;
  • quantum defect;
  • excitation energies


Quantum defect analysis is applied to time-dependent density functional theory (TDDFT) calculations of the Rydberg series of the He and Be atoms. The focus of the present study is on excitation energies obtained with different exchange-correlation potentials and kernels. Excitation energies are reobtained from the quantum defect values, and it is shown that these energies can be very accurately obtained from knowledge of the quantum defect alone. TDDFT results are compared within the adiabatic local density approximation for the case in which all virtual states are included in the calculation with results obtained when the number of states is truncated. Quantum defect analysis is used to demonstrate that truncation leads to serious errors. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006