Single Excitation Theories in Q-Chem

CIS Methods

  • Excited states are computed starting from a Hartree-Fock reference

  • Provides qualitatively correct descriptions of singly excited states

  • Geometries and frequencies comparable to ground-state Hartree-Fock results

  • Efficient, direct algorithm for computing energies, analytic gradients, and second derivatives

  • Perturbative doubles correction via CIS(D) and SOS-CIS(D)

    • Reduces the errors in CIS by a factor of two or more (to roughly that of MP2)

    • RI-CIS(D) and RI-CIS(D0) methods for faster correlated excited-state calculations

borane pic


Time-Dependent DFT (TDDFT)