Relativistic four- and two-component calculations of parity violation effects in chiral tungsten molecules of the form NWXYZ (X, Y, Z = H, F, Cl, Br, or I).

Parity violation (PV) effects to the electronic ground state structure for a series of chiral tungsten molecules of the type NWXYZ (X, Y, Z = H, F, Cl, Br, or I) are compared using four- (Dirac) and two- (X2C) component relativistic Hartree-Fock and density functional theories. The results show the computationally more affordable two-component X2C approach yields accurate results for all molecules investigated. The PV energy differences between the two enantiomers range from as little as 0.4 Hz for NWClBrI to 140 Hz for NWHClI using a generalized gradient approximation including exact exchange (B3LYP). The W-N stretching mode in these molecules lies in the experimentally favorable CO(2) laser frequency range, and we therefore investigated PV effects in vibrational transitions using a single normal mode analysis. Here the PV frequency shift between the two enantiomers ranges from 1.6 mHz for NWFBrI to 710 mHz for NWHClI. Thus these types of molecules could be useful for the future detection of PV effects in chiral molecules.

NWHClI: a small and compact chiral molecule with large parity-violation effects in the vibrational spectrum.

Small but mighty: An unprecedented large parity-violation energy difference of 0.7 Hz for the N-W stretching frequency of N≡WHClI, which conveniently lies in the CO(2) laser frequency range, is predicted from relativistic density functional theory. This result could lead to the first successful detection of such effects in chiral molecules.

A highly accurate potential energy curve for the mercury dimer.

The potential energy curve of the electronic ground state of the mercury dimer based on CCSD(T) calculations at the complete basis set (CBS) limit, including corrections for the full triples DeltaT and explicit spin-orbit (SO) interactions at the CCSD(T) level of theory, is presented. In the far long-range part, the potential energy curve is complemented by symmetry-adapted perturbation theory calculations. Potential curves of an analytically simple, extended Lennard-Jones form are obtained from very accurate fits to the CBS/CCSD(T)+SO and CBS/CCSD(T)+SO+DeltaT data. The Hg(2) potential curves yield dissociation energies of D(e)=424/392 cm(-1) and equilibrium distances of r(e)=3.650/3.679 A at the CBS/CCSD(T)+SO and CBS/CCSD(T)+SO+DeltaT levels of theory, respectively. By including perturbative quadruple corrections in our coupled-cluster calculations and corrections from correlating the 4f-core, we arrive at a final dissociation energy of D(e)=405 cm(-1), in excellent agreement with the experimentally estimated value of 407 cm(-1) by Greif and Hensel. In addition, the rotational and vibrational spectroscopic constants as well as the second virial coefficient B(T) in dependence of the temperature T are calculated and validated against available experimental and theoretical data.

Energy-consistent pseudopotentials for the 5d elements--benchmark calculations for oxides, nitrides, and Pt(2).

The performance of new relativistic energy-consistent pseudopotentials for the 5d elements, adjusted to atomic valence spectra from multiconfiguration Dirac-Hartree-Fock calculations (J. Chem. Phys. 2009, 130, 164108.), is examined in coupled cluster and multireference configuration interaction benchmark calculations for the diatomics HfO, TaO, WO, ReN, OsN, IrN, and Pt(2), with basis sets of up to quintuple-zeta quality. The final accuracy reached for the oxides and nitrides, with corrections for pseudopotential errors (contributions from 4f shell correlation, for example), is 0.3 pm for bond lengths and 17 cm(-1) (1.5%) for harmonic vibrational frequencies. The spectroscopic constants of the ground state of Pt(2) can be reproduced with deviations of 3 pm for the bond length and 1 cm(-1) for the vibrational frequency, without any correction for pseudopotential errors.

Accurate potential energy surface and calculated spectroscopic properties for CdH2 isotopomers.

Ab initio calculations employing the coupled cluster method CCSD(T), in conjunction with a small-core pseudopotential for the cadmium atom, have been employed to construct a near-equilibrium potential energy function (PEF) and an electric dipole moment function (EDMF) for CdH(2). The significance of the spin-orbit interaction was checked and found to be of minor importance. Making use of two pieces of experimental information for the most abundant isotopomer (114)CdH(2), we obtained a refined PEF, which, within variational calculations of rovibrational states and wave functions, reproduces all available experimental data (S. Yu, A.Shayesteh, and P. F. Bernath, J. Chem. Phys. 2005, 122, 194301) very well. In addition, numerous predictions are made. In particular, the nu(2) band origins for (114)CdH(2) and (114)CdD(2) are predicted at 605.9 and 436.9 cm(-1), respectively, and the state perturbing the e parity levels of the (0,0(0),1) state of (114)CdH(2) at J = 12-17 is identified as the (0,3(3),0) state. Assignments for further perturbations found in the emission spectra are given as well.

Energy-consistent pseudopotentials and correlation consistent basis sets for the 5d elements Hf-Pt.

New relativistic energy-consistent pseudopotentials have been generated for the 5d transition metals Hf-Pt. The adjustment was done in numerical two-component multiconfiguration Hartree-Fock calculations, using atomic valence-energy spectra from four-component multiconfiguration Dirac-Hartree-Fock calculations as reference data. The resulting two-component pseudopotentials replace the [Kr]4d(10)4f(14) cores of the 5d transition metals and can easily be split into a scalar-relativistic and a spin-orbit part. They reproduce the all-electron reference energy data with deviations of approximately 0.01 eV for configurational averages and approximately 0.05 eV for individual relativistic states. Full series of correlation consistent basis sets from double to quintuple-zeta have also been developed in this work for use with the new pseudopotentials. In addition, all-electron triple-zeta quality correlation consistent basis sets are also reported in order to provide calibration for the pseudopotential treatment. The accuracy of both the pseudopotentials and basis sets are assessed in extensive coupled cluster benchmark calculations of atomic ionization potentials, electron affinities, and selected excitation energies of all the 5d metal atoms, including the effects of spin-orbit coupling.

Structures, inversion barriers, and parity violation effects in chiral SeOXY molecules (X,Y = H, F, Cl, Br, or I).

Parity violation (PV) effects for a series of chiral molecules of the type SeOXY (X,Y = H, F, Cl, Br, or I) are predicted from four-component relativistic Hartree-Fock and density functional theory. All optimized SeOXY structures are nonplanar with large inversion barriers ranging from 23 to 55 kcal/mol; thus, all SeOXY molecules remain enantiomeric stable on the laboratory time scale. The variation in PV between the different methods applied is small enough for each molecule to allow for an accurate prediction of these effects. At the respective equilibrium geometries the enantiomers exhibit parity violating energy shifts of up to 17 Hz. The Se-O stretching mode of all investigated SeOXY molecules lies in the experimentally favorable CO(2) laser range of approximately 1000 cm(-1). We therefore investigated PV effects in vibrational transitions along a single normal mode using Dirac-Kohn-Sham theory. The PV energy differences in the fundamental Se-O stretching mode amount up to 110 mHz (largest for SeOClI) and are larger compared to the C-F stretching mode of CHFBrI previously investigated. Hence these SeOXY molecules are ideal candidates for the future experimental gas-phase detection of PV in vibrational spectra of chiral molecules.

On the performance of two-component energy-consistent pseudopotentials in atomic Fock-space coupled cluster calculations.

The four-component atomic intermediate-Hamiltonian Fock-space coupled cluster (IHFSCC) code of Landau et al. [J. Chem. Phys. 115, 6862 (2001)] has been adapted to two-component calculations with relativistic pseudopotentials of the energy-consistent variety. Recently adjusted energy-consistent pseudopotentials for group 11 and 12 transition elements as well as group 13 and 14 post-d main group elements, which were fitted to atomic valence spectra from four-component multiconfiguration Dirac-Hartree-Fock calculations, are tested in IHFSCC calculations for ionization potentials, electron affinities, and excitation energies of a variety of atoms and ions. Where comparison is possible, the deviations from experimental data are in good agreement with those found in previously published IHFSCC all-electron calculations: experimental data are usually reproduced within a few hundred wavenumbers.

Energy-consistent relativistic pseudopotentials for the 4d elements: atomic and molecular applications.

Recently reported energy-consistent relativistic pseudopotentials have been used with series of matching correlation consistent basis sets in benchmark calculations of various atomic and molecular properties. The basis set convergence of the 4d metal electron affinities and 5s2-->5s0 excitation energies are reported at the CCSD(T) level of theory, and the effects of valence and 4s4p correlation are investigated. In addition the impact of correlating the low-lying 3d electrons was also studied in all-electron Douglas-Kroll-Hess (DKH) calculations, which also included the ionization potentials and 5s2-->5s1 excitation energies. For all four atomic properties, higher order coupled cluster calculations through CCSDTQ are reported. The final calculated values are generally all within 1 kcal/mol of experiment. A notable exception is the ionization potential of Tc, the currently accepted experimental value of which is suggested to be too high by about 3 kcal/mol. Molecular calculations are also reported for the low-lying electronic states of ZrO and RuF, as well as the ground electronic state of Pd2. The effects of spin-orbit coupling are investigated for these cases in pseudopotential calculations. Wherever possible, the pseudopotential results have been calibrated against DKH calculations with correlation consistent basis sets of triple-zeta quality. In all cases the calculated data for these species are in very good agreement with experiment. In particular, the correct electronic ground state for the RuF molecule (4Phi92) was obtained, which was made possible by utilizing systematic sequences of correlation consistent basis sets.

Energy-consistent relativistic pseudopotentials and correlation consistent basis sets for the 4d elements Y-Pd.

Scalar-relativistic pseudopotentials and corresponding spin-orbit potentials of the energy-consistent variety have been adjusted for the simulation of the [Ar]3d(10) cores of the 4d transition metal elements Y-Pd. These potentials have been determined in a one-step procedure using numerical two-component calculations so as to reproduce atomic valence spectra from four-component all-electron calculations. The latter have been performed at the multi-configuration Dirac-Hartree-Fock level, using the Dirac-Coulomb Hamiltonian and perturbatively including the Breit interaction. The derived pseudopotentials reproduce the all-electron reference data with an average accuracy of 0.03 eV for configurational averages over nonrelativistic orbital configurations and 0.1 eV for individual relativistic states. Basis sets following a correlation consistent prescription have also been developed to accompany the new pseudopotentials. These range in size from cc-pVDZ-PP to cc-pV5Z-PP and also include sets for 4s4p correlation (cc-pwCVDZ-PP through cc-pwCV5Z-PP), as well as those with extra diffuse functions (aug-cc-pVDZ-PP, etc.). In order to accurately assess the impact of the pseudopotential approximation, all-electron basis sets of triple-zeta quality have also been developed using the Douglas-Kroll-Hess Hamiltonian (cc-pVTZ-DK, cc-pwCVTZ-DK, and aug-cc-pVTZ-DK). Benchmark calculations of atomic ionization potentials and 4d(m-2)5s(2)-->4d(m-1)5s(1) electronic excitation energies are reported at the coupled cluster level of theory with extrapolations to the complete basis set limit.

On the spectroscopic and thermochemical properties of ClO, BrO, IO, and their anions.

A coupled cluster composite approach has been used to accurately determine the spectroscopic constants, bond dissociation energies, and heats of formation for the X1(2)II(3/2) states of the halogen oxides ClO, BrO, and IO, as well as their negative ions ClO-, BrO-, and IO-. After determining the frozen core, complete basis set (CBS) limit CCSD(T) values, corrections were added for core-valence correlation, relativistic effects (scalar and spin-orbit), the pseudopotential approximation (BrO and IO), iterative connected triple excitations (CCSDT), and iterative quadruples (CCSDTQ). The final ab initio equilibrium bond lengths and harmonic frequencies for ClO and BrO differ from their accurate experimental values by an average of just 0.0005 A and 0.8 cm-1, respectively. The bond length of IO is overestimated by 0.0047 A, presumably due to an underestimation of molecular spin-orbit coupling effects. Spectroscopic constants for the spin-orbit excited X2(2)III(1/2) states are also reported for each species. The predicted bond lengths and harmonic frequencies for the closed-shell anions are expected to be accurate to within about 0.001 A and 2 cm-1, respectively. The dissociation energies of the radicals have been determined by both direct calculation and through use of negative ion thermochemical cycles, which made use of a small amount of accurate experimental data. The resulting values of D0, 63.5, 55.8, and 54.2 kcal/mol for ClO, BrO, and IO, respectively, are the most accurate ab initio values to date, and those for ClO and BrO differ from their experimental values by just 0.1 kcal/mol. These dissociation energies lead to heats of formation, DeltaH(f) (298 K), of 24.2 +/- 0.3, 29.6 +/- 0.4, and 29.9 +/- 0.6 kcal/mol for ClO, BrO, and IO, respectively. Also, the final calculated electron affinities are all within 0.2 kcal/mol of their experimental values. Improved pseudopotential parameters for the iodine atom are also reported, together with revised correlation consistent basis sets for this atom.

A systematic ab initio study of the equilibrium geometry and vibrational wave numbers of bismuthine.

The equilibrium structure and the harmonic and anharmonic force fields of BiH(3) are determined by high-level ab initio calculations using a variety of correlation treatments, basis sets, and pseudopotentials, partly in combination with core polarization potentials. Spin-orbit effects are included by a configuration interaction treatment. This systematic study serves to establish a reliable computational protocol for such calculations and, in particular, to minimize basis set superposition errors through an improved new basis set and/or counterpoise corrections. Using the recommended procedures, the best ab initio results for the equilibrium geometry and the fundamental vibrational wave numbers are in good agreement with the available experimental data, which further supports the recent spectroscopic identification of BiH(3). The ground-state total atomization energy of BiH(3) is predicted to be 153.1 kcal/mol.