EXCITATION-ENERGIES IN BERYLLIUM - A COMPARISON OF MULTICONFIGURATIONAL LINEAR RESPONSE AND FULL CONFIGURATION-INTERACTION CALCULATIONS
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abstract
Using a (9s9p5d) contracted GTO basis we have calculated low-lying excitation energies of singlet and triplet symmetry for the Be atom using full CI, ACI (1s) with double occupancy in the 1s orbital, multiconfiguration linear response (MCLR), and MCSCF approaches. The full CI results agree very closely with the experimental excitation energies except for higher excitations where obvious basis set defects occur. The MCLR calculations shows that with an adequately chosen MCSCF reference state the MCLR calculation is capable of mimicking the full CI results. The MCLR results are closer to the full CI results than the CI(1s). The MCSCF excitation energies show that this approach can only be used with extreme care to determine excitation energies. 1986 American Institute of Physics.
