Theoretical study of the spectra of CuH and CuD

Spin-orbit coupling in low-lying electronic states of CuH

Potential energy curves for the low-lying electronic states of CuH have been calculated using the MRCI method with a large active space containing the 3d, 4s, 4pz and 3d' orbitals of the copper atom. All electronic states of CuH correlating with the 3d10 4s1 (2S) and 3d9 4s2 (2D) states of Cu were included, and spin-orbit corrections were calculated using the MRCI wavefunctions. Potential energy curves were obtained for individual Ω states, and the Einstein A coefficients were computed for the spin-forbidden transitions from the low-lying electronic states to the X1Σ+ ground state. Diagonal and off-diagonal elements of the spin-orbit Hamiltonian matrix were calculated for the X1Σ+, A1Σ+, 13Σ+, 23Σ+, 11Π, 13Π, 11Δ and 13Δ states, and the mixing of vibronic wavefunctions was investigated using the eigenvectors. The available experimental data on vibrational levels of the A1Σ+ excited state of CuH and CuD were combined in a multi-isotopologue Birge-Sponer plot, and the ab initio data on the unobserved vibrational levels were used for a more accurate extrapolation, resulting in a new experimental value for the equilibrium dissociation energy (De) of the CuH molecule. The De value for the ground state of CuH was determined to be 22 630 ± 250 cm-1, resulting in D0 values of 2.686 and 2.720 eV for CuH and CuD, respectively. Therefore, new experimental values for the bond dissociation enthalpies of CuH and CuD are reported to be 262.9 ± 3 and 266.2 ± 3 kJ mol-1, respectively.

Systematically convergent basis sets for transition metals. I. All-electron correlation consistent basis sets for the 3d elements Sc-Zn

Sequences of basis sets that systematically converge towards the complete basis set (CBS) limit have been developed for the first-row transition metal elements Sc-Zn. Two families of basis sets, nonrelativistic and Douglas-Kroll-Hess (-DK) relativistic, are presented that range in quality from triple-zeta to quintuple-zeta. Separate sets are developed for the description of valence (3d4s) electron correlation (cc-pVnZ and cc-pVnZ-DK; n = T,Q, 5) and valence plus outer-core (3s3p3d4s) correlation (cc-pwCVnZ and cc-pwCVnZ-DK; n = T,Q, 5), as well as these sets augmented by additional diffuse functions for the description of negative ions and weak interactions (aug-cc-pVnZ and aug-cc-pVnZ-DK). Extensive benchmark calculations at the coupled cluster level of theory are presented for atomic excitation energies, ionization potentials, and electron affinities, as well as molecular calculations on selected hydrides (TiH, MnH, CuH) and other diatomics (TiF, Cu2). In addition to observing systematic convergence towards the CBS limits, both 3s3p electron correlation and scalar relativity are calculated to strongly impact many of the atomic and molecular properties investigated for these first-row transition metal species.

Two-component relativistic methods for the heaviest elements

Different generalized Douglas-Kroll transformed Hamiltonians (DKn, n=1, 2,...,5) proposed recently by Hess et al. are investigated with respect to their performance in calculations of the spin-orbit splittings. The results are compared with those obtained in the exact infinite-order two-component (IOTC) formalism which is fully equivalent to the four-component Dirac approach. This is a comprehensive investigation of the ability of approximate DKn methods to correctly predict the spin-orbit splittings. On comparing the DKn results with the IOTC (Dirac) data one finds that the calculated spin-orbit splittings are systematically improved with the increasing order of the DK approximation. However, even the highest-order approximate two-component DK5 scheme shows certain deficiencies with respect to the treatment of the spin-orbit coupling terms in very heavy systems. The meaning of the removal of the spin-dependent terms in the so-called spin-free (scalar) relativistic methods for many-electron systems is discussed and a computational investigation of the performance of the spin-free DKn and IOTC methods for many-electron Hamiltonians is carried out. It is argued that the spin-free IOTC rather than the Dirac-Coulomb results give the appropriate reference for other spin-free schemes which are based on approximate two-component Hamiltonians. This is illustrated by calculations of spin-free DKn and IOTC total energies, r(-1) expectation values, ionization potentials, and electron affinities of heavy atomic systems.