THE RELATIVISTIC FOCK-SPACE COUPLED-CLUSTER METHOD FOR MOLECULES - CDH AND ITS IONS

The relativistic coupled-cluster method starts from the Dirac-Coulomb- Breit Hamiltonian in its low-frequency approximation and includes corr elation by Fock-space coupled-cluster with single and double excitatio ns. One- and two-component approximations using the-Douglas-Kroll tran sformation are also tested. Significant relativistic effects are found for CdH, with bond length contracting from 1.820 to 1.778 Angstrom (e xperimental 1.781 Angstrom) and binding energies decreasing from 0.87 to 0.70 eV (experimental 0.68 eV). The binding energy of the cation in creases by 0.1 eV upon inclusion of relativity. The electron affinity of the molecule is 0.44 eV. The Douglas-Kroll values include nearly al l the relativistic correction. (C) 1988 American Institute of Physics. [S0021-9606(98)01609-2].