Nikolai B. Balabanov

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.

Hg+Br-->HgBr recombination and collision-induced dissociation dynamics.

A global potential energy surface has been constructed for the system HgBr+Ar-->Hg+Br+Ar to determine temperature dependent rate constants for the collision-induced dissociation (CID) and recombination of Hg and Br atoms. The surface was decomposed using a many-body expansion. Accurate two-body potentials for HgBr, HgAr, and ArBr were calculated using coupled cluster theory with single and double excitations and a perturbative treatment of triple excitations [CCSD(T)], as well as the multireference averaged coupled pair functional method. Correlation consistent basis sets were used to extrapolate to the complete basis set limit and corrections were included to account for scalar and spin-orbit relativistic effects, core-valence correlation, and the Lamb shift. The three-body potential was computed with the CCSD(T) method and triple-zeta quality basis sets. Quasiclassical trajectories using the final analytical potential surface were directly carried out on the CID of HgBr by Ar for a large sampling of initial rotational, vibrational, and collision energies. The recombination rate of Hg and Br atoms is a likely first step in mercury depletion events that have been observed in the Arctic troposphere during polar sunrise. The effective second order rate constant for this process was determined in this work from the calculated CID rate as a function of temperature using the principle of detailed balance, which resulted in k(T) = 1.2 x 10(-12) cm(3) molecule(-1) s(-1) at 260 K and 1 bar pressure.

A systematic ab initio study of the structure and vibrational spectroscopy of HgCl2, HgBr2, and HgBrCl

Near-equilibrium potential energy and dipole moment functions have been calculated for the linear mercury halide molecules HgCl2, HgBr2, and HgBrCl using highly correlated coupled cluster wave functions and large correlation consistent basis sets. After extrapolation to the complete basis set limit, additional corrections due to core-valence correlation and relativity were included in the final anharmonic potential energy functions (PESs). The fitted PESs and dipole moment functions were then used in variational calculations of the low-lying rovibrational band origins. Both the asymmetric stretch and symmetric bend fundamental bands are predicted to carry significant oscillator strength for all three species. A wide range of spectroscopic properties are accurately predicted, which should facilitate the observation of these species by high resolution spectroscopy.

Accurate theoretical near-equilibrium potential energy and dipole moment surfaces of HgClO and HgBrO.

The complexes HgBrO and HgClO have been previously determined by ab initio methods to be strongly bound and were suggested to be important intermediates during mercury depletions events observed in the polar troposphere. In the present work accurate near-equilibrium potential energy surfaces (PESs) of these species are reported. The PESs are determined using accurate coupled cluster methods and a series of correlation consistent basis sets with subsequent extrapolation to the complete basis set limit. Additive corrections for both core-valence correlation energy and relativistic effects are also included. The anharmonic ro-vibrational spectra of HgBrO and HgClO have been calculated in variational calculations. Strong infrared band strengths are predicted for all fundamentals in these species. The spin-orbit splitting dominates over the vibronic coupling effect in both HgClO and HgBrO. The Renner-Teller vibronic energy levels corresponding to the bending mode of these molecules are calculated via perturbation theory.