Using an asymmetric Lanczos chain algorithm for the calculation of the coupled cluster linear response functions at the coupled cluster singles and doubles (CCSD) and coupled cluster singles and approximate iterative doubles (CC2) levels of approximation, we have calculated the mean excitation energies of the noble gases He, Ne and Ar, and of the hydrogen molecule (H-2). Convergence with respect to the one-electron basis set was investigated in detail for families of correlation-consistent basis sets including both augmentation and core-valence functions. We find that the electron correlation effects at the CCSD level change the mean excitation energies obtained at the uncorrelated Hartree-Fock level by about 1%. For the two-electron systems He and H-2, our CCSD results (for a Lanczos chain length equal to the full excitation space), I-0 = 42.28 eV (helium) and I-0 = 19.62 eV (H-2), correspond to full configuration interaction results and are therefore the exact, non-relativistic theoretical values for the mean excitation energy of these two systems within the Bethe theory for the chosen basis set and, in the case of H-2, at the experimental equilibrium geometry.
Molecular Physics, 2014, Vol 112, Issue 5-6, p. 751-761
mean excitation energy coupled cluster full configuration interaction helium neon argon hydrogen molecule asymmetric Lanczos chain algorithm GAUSSIAN-BASIS SETS OSCILLATOR-STRENGTH DISTRIBUTION ELECTRONICALLY EXCITED-STATES NUCLEAR MAGNETIC SHIELDINGS RESPONSE FUNCTIONS HARTREE-FOCK DIRECTIONAL CHARACTERISTICS POLARIZATION-CONSISTENT SPECTRAL MOMENTS CROSS-SECTIONS; Quantum Chemistry; Computational Chemistry; Stopping Power; Nobel gas; Hydrogen; Coupled Cluster; Mean excitation energy; hadron therapy; The Faculty of Science