Using an asymmetric-Lanczos-chain algorithm for the calculation of the coupled cluster linear response functions at the CCSD and CC2 levels of approximation, we have calculated the mean excitation energies of the noble gases He, Ne and Ar, and of the hydrogen molecule H2. Convergence with respect to the one-electron basis set was investigated in details for families of correlation consistent basis sets including both augmentation and core-valence functions. We nd 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 H2, our CCSD results (for a Lanczos chain length equal to the full excitation space), I0 = 42:28 eV (Helium) and I0 = 19:62 eV (H2), correspond to full conguration 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 H2, at the experimental equilibrium geometry.
Molecular Physics, 2013, Vol 112, Issue 5-6, p. 751-761
Quantum Chemistry; Computational Chemistry; Stopping Power; Nobel gas; Hydrogen; Coupled Cluster; Mean excitation energy; hadron therapy; The Faculty of Science; 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