Stuttgart Group Research Articles

Instanton calculations of tunneling splittings in chiral molecules.

We report the ground state tunneling splittings (ΔE± ) of a number of axially chiral molecules using the ring-polymer instanton (RPI) method (J. Chem. Phys., 2011, 134, 054109). The list includes isotopomers of hydrogen dichalcogenides H2 X2 (X = O, S, Se, Te, and Po), hydrogen thioperoxide HSOH and dichlorodisulfane S2 Cl2 . Ab initio electronic-structure calculations have been performed on the level of second-order Møller-Plesset perturbation (MP2) theory either with split-valance basis sets or augmented correlation-consistent basis sets on H, O, S, and Cl atoms. Energy-consistent pseudopotential and corresponding triple zeta basis sets of the Stuttgart group are used on Se, Te, and Po atoms. The results are further improved using single point calculations performed at the coupled cluster level with iterative singles and doubles and perturbative triples amplitudes. When available for comparison, our computed values of ΔE± are found to lie within the same order of magnitude as values reported in the literature, although RPI also provides predictions for H2 Po2 and S2 Cl2 , which have not previously been directly calculated. Since RPI is a single-shot method which does not require detailed prior knowledge of the optimal tunneling path, it offers an effective way for estimating the tunneling dynamics of more complex chiral molecules, and especially those with small tunneling splittings.

A Study on Pathway and QSPR Models for Debromination of PBDEs with Pseudopotential Method

Neutral PBDEs congeners and their corresponding radical anions were studied with the pseudopotential method of stuttgart group (SDD) effective-core potentials basis set for the bromine atoms and the all-electron basis set for all other atoms. The pseudopotential method can be used for compounds containing heavy elements with relativistic effects and can reduce the computational time. The quantitative structure property relationship (QSPR) study was also performed in this work to develop models to predict the normolized reaction rate constants for the reductive debromination of polybrominated diphenyl ethers (PBDEs) by zero-valent iron (ZVI). The partial least squares regression (PLSR), principal component analysis-multiple linear regression analysis (PCA-MLR), and back propagation artificial neural network (BP-ANN) approaches were employed for the QSPR study between the molecular descriptors and the logarithm of normalized reaction rate constants of fourteen selected BDE congeners. The results show that the ANN models could be more satisfactorily to predict the rate constants than the PLSR and PCA-MLR models.

Hybrid Ab initio/EFP approach for calculating d‐d absorption spectrum of hexaammineruthenium(II) ion in aqueous solutions

AbstractAb initio quantum chemical strategies for quantitatively predicting the lowest (1Ag → 1T1g) vertical d‐d excitation energy of hexaammineruthenium(II) ion in aqueous solution are discussed. The scalar‐relativistic ECP/valence basis set on Ru atom developed by the Stuttgart group in a combination with the state‐average CASSCF(d) approach, followed by multiconfigurational quasi‐degenerate second‐order perturbation theory (MCQDPT2) to account for differential correlation effects is proved to be an adequate tool to reproduce the experimental absorption spectrum of the complex for a variety of AO basis sets on ligand atoms. In addition, different ab initio methodologies are examined in order to predict the ground state geometry which is consistent with the follow‐up excitation spectrum calculations. It is observed that the use of the optimized structures of a hypothetical gas‐phase complex lead to substantial underestimation of excitation energies. Solvent effects strongly influence the excitation energy though indirectly, mainly by means of changing the ground state geometry of the solvated complex when compared with the vacuum one. In particular, the ground state structure of the complex surrounded by effective fragments simulating water molecules provides the lowest CASSCF/MCQDPT excitation energy estimate to be within 25,500–26,400 cm−1, in a fair agreement with the experimentally measured value of 25,600 cm−1. At the same time, direct incorporation of solvation effects causes only minor change in the estimated transition energies, within several hundred cm−1. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Positronium formation in fused quartz: Experimental evidence of delayed formation

The young-age broadening was found and explained with the delayed thermalization of Ps by Stuttgart group. According to the spur or blob model, Ps formation even at ∼100 ps might be possible in suitable materials, such as in fused quartz, even at the room temperature. We have obtained the experimental evidence of delayed Ps formation that gives the young-age broadening in fused quartz by the inhibition of slower Ps formation by applying electric fields on it.

The NaDyBr4 complex; its molecular structure and thermodynamic properties

The molecular geometry, vibrational frequencies, relative stabilities, and some thermodynamic properties of different isomers of the NaDyBr4 complex were determined by computation. We investigated, to our knowledge for the first time for such a complex, the possible effect of the partially filled 4f orbitals on the molecular properties of an MLnX4 complex by using a “small core” effective core potential of the Stuttgart group. The tridentate complex, with three Na–Br bridges, was found to be the ground-state structure with the bidentate one only about 4–6 kJ/mol higher in energy. The relative abundance of these isomers changes with temperature and at the high-temperature conditions of a metal halide lamp the bidentate isomer is the more abundant isomer.

Ab initio study on the spectroscopy of CuCl2. II. Benchmark calculations on the X 2Πg-C 2Δg and X 2Πg-D 2Δg transitions

The X (2)Pi(g)-C (2)Delta(g) and X (2)Pi(g)-D (2)Delta(g) transitions on CuCl(2) have been studied using the most sophisticated nondynamic and dynamic electronic correlation treatments. We report here ab initio benchmark calculations using especially developed basis sets to study, at the complete active space self-consistent field plus second-order Møller-Plesset algorithm (CASSCF+CASPT2) and CASSCF+ACPF levels, the transition energies as well as the corresponding equilibrium geometries (ACPF-averaged coupled pair functional). The spin-orbit (SO) effects of both atoms were included in a second step through the effective Hamiltonian formalism, using the calibrated SO effective potentials developed by the Stuttgart group. Without SO at the CASSCF+ACPF level, the vertical excitation energy for the (2)Delta(g) state is 6711 cm(-1) and the symmetric stretching equilibrium Cu-Cl distance is 4.04 a.u. The inclusion of the SO effects leads to a pure (2)Delta(g) Omega=5/2C state and a Omega=3/2 (0.7% (2)Pi(g),99.3% (2)Delta(g))D state. The calculated transition energies for the C and D states are 6340 and 8020 cm(-1), in good agreement with the spin-orbit splitting recent values from gas-phase and rare-gas matrix isolation laser induced fluorescence experiments. The present benchmark results show, as was recently done for the X (2)Pi(g)-(2)Sigma(g) transition, the rather poor performance of all the density functional theory-based descriptions for the (2)Delta(g) state, which largely overestimate its T(e), systematically placing it around 19 000 cm(-1). The CASSCF+CASPT2 method also overestimates, by around 50%, the X (2)Pi(g)-(2)Delta(g) transition energy, showing that only large variational calculations can produce reliable spectroscopic results for this kind of complex systems where delicate electronic correlation effects have to be carefully dealt with.

HeBr2 complex: ground-state potential and vibrational dynamics from ab initio calculations

The three-dimensional interaction potential for HeBr2 was studied using a coupled-cluster (CCSD(T)) method. In our calculations, the Stuttgart group (SDD) effective-core potentials, augmented with diffusion (sp) and polarization (3df) functions (denoted SDD+G(3df)), basis sets are employed for the bromine atoms. For the He atom, the augmented correlation-consistent aug-cc-pV5Z basis set, supplemented with a set of bond functions, is used. The potential energy surface is constructed by fitting the CCSD(T) calculated ab initio data to an analytical expression. The present ground-state potential for HeBr2 shows a double-minimum topology, with wells for both linear and T-shaped configurations. Bound-state calculations are carried out and the lowest vibrational levels are assigned to linear and T-shaped isomers. Dissociation energies and vibrationally averaged structures for both species are determined and found to be in very good agreement with the available experimental data.

Ab initio study on the spectroscopy of CuCl2. I. Benchmark calculations on the X2Pig - 2Sigmag+ transition.

The modern theoretical predictions on the LambdaSSigma nature of the ground state of CuCl2 have led to different answers, depending on the type (DFT-based or ab initio) and the quality of the electronic correlation treatment; for this reason the X2Pig - 2Sigmag+ transition energy has been predicted to range from -1856 to +5887 cm(-1). The physical problem at hand lies in the difficulty of accurately describing the orientation of the 3d hole on the central Cu2+(3d9)/Cu+(3d94s1) ion (in the field of both chlorine ions), which implies the need of the most sophisticated nondynamic and dynamic electronic correlation treatments. We report here ab initio benchmark calculations using especially developed basis sets to study, at the CASSCF + CASPT2 and CASSCF + ACPF levels, the transition energy as well as the corresponding equilibrium geometries. The spin-orbit (SO) effects of both atoms were included in a second step through the effective Hamiltonian formalism, using the calibrated SO effective potentials developed by the Stuttgart group. Without SO at the CASSCF + ACPF level, the ground state is X2Pig but the vertical transition energy to the 2Sigmag+ is only 99 cm(-1) at 3.95 a.u. The inclusion of the SO effects leads to a Omega = 1/2 (59% 2Pig,41% 2Sigmag+) ground state, in contradiction with the Omega experimental value of 3/2. In a last step we show that the SO effects (and therefore the final Omega ordering) are critically dependent on the LambdaSSigma electronic energies, so that it is not impossible that the Omega ordering is actually changed. For theoreticians interest in this matter is not purely academic, since many properties of organometallic complexes are linked to such delicate physical effects.

Thermal spike analysis of interface mixing induced by swift heavy ions

Interface mixing induced by energetic ions is discussed, applying the author’s thermal spike model. Diffusion in the ion-induced melt is assumed. An expression is derived for the variation of the mixing rate k with the electronic stopping power Se. The experimental results recently reported by the Stuttgart group on NiO, ZnO, CuO, and Cu2O layers on SiO2 substrate are analyzed and good agreement is found with the predictions of the model for k and for the threshold of Se for melt formation. Average diffusion coefficients in the spike are estimated, and Dd≈0.053, 0.03, and 0.004 cm2/s are obtained for Zn, Ni, and Cu ions, respectively.

Ab initio calculations with effective core potentials on trivalent lanthanide-terpyridine complexes

The electronic structures of complexes of terpyridine (tpy) with trivalent lanthanides (Ln) were calculated using ab initio methods with effective core potentials at Hartree–Fock and post-Hartree–Fock levels of theory. The quasirelativistic large-core (with 4f electrons included in the core) pseudopotentials of the Stuttgart group were chosen for the Ln atoms. The variation of several properties of the Ln(tpy)3+ complexes was studied for the whole Ln series. It was shown that there was a monotonous variation for all properties (geometrical and energetic) along the Ln series, except for Mulliken charges on the metal atom. Calculations were performed on three complexes of known solid-state structure. The difference between experimental and calculated geometries is discussed; for all structures, it is found to be lower than 0.2 A. In all cases, the relative order from one complex to another is conserved.

Density Functional Derived Structures and Molecular Properties of Nickel Dithiolenes and Related Complexes

The molecular and electronic structure of the planar nickel dithiolene (1c, R = H) and of related complexes derived from nickel dithiolene by replacement of Ni by Pd (palladium dithiolene, 2c, R = H) or by Pt (platinum dithiolene, 3c, R = H), or by replacement of S by NH (nickel diiminolene, 1a, R = H), O (nickel dioxylene, 1b, R = H) or Se (nickel diselenolene, 1d, R = H), were studied by density functional theory using the B3LYP functional and the valence triple-zeta basis set 6-311+G* for all atoms except Pd and Pt. For the latter atoms the quasirelativistic effective core potentials of the Stuttgart group were employed. The molecular structure of nickel dithiolene (1c, R = H) is satisfactorily reproduced by DFT calculations. The geometry of the corresponding platinum complexes 3a–3d is more sensitive to relativistic effects, resulting in the contraction of the X–Pt bonds. As shown with the metal dithiolenes, the two ligands are structurally related to mononegative ions of open shell structure. The C–C bond lengths of the complexes are close to those of aromatic and chain-type polymethine structures (about 1.4 A). The nickel dithiolene (1c, R = H) and related complexes have D2h symmetry and are 14 π-electron systems with 10 π-electrons at the ligands and 4 π-electrons at the metal center. The natural population analysis has confirmed that metal M++ does accept electrons from the ligands but to a lesser extent than expected. The empty d-orbitals of M++ are only partly occupied in the molecular ground state. The positive charge of the metal decreases in the order Ni > Pd > Pt. The 1H chemical shifts and the nucleus-independent chemical shifts (NICSs) of the ring moieties calculated by GIAO-DFT display a pronounced electron delocalization. In agreement with the calculated C–C bond lengths the 1H chemical shifts and the NICS values show a marked bond delocalization. The NICS values show a change of the aromatic delocalization in the order Ni > Pd O < S < Se. The wave numbers of the IR spectra of the complexes calculated by DFT are grouped in separate frequency regions. The very intense absorption of 1c (R = H) in the visible region of the spectrum is surprisingly well reproduced by ab initio single-only configuration interaction calculations. While the color band of the palladium complex is predicted to be red-shifted relative to the nickel complex, a blue shift is calculated on passing from the palladium to the platinum complex. The blue shift is, in part, due to the relativistic contraction of bond lengths in the Pt complexes.

Spin-orbit interaction in heavy group 13 atoms and TlAr

The scalar-relativistic energy-consistent 3-valence-electron (3-ve) pseudopotentials of the Stuttgart group for the heavy group 13 atoms GaTl have been supplemented by small-core (13-ve and 21-ve) ones as well as by spin-orbit potentials adjusted to Dirac-Fock data. These potentials have been applied, in correlated valence ab initio calculations, to atomic spin-orbit splittings as well as to ground- and excited-state potential curves of the TlAr complex.

The accuracy of the pseudopotential approximation. II. A comparison of various core sizes for indium pseudopotentials in calculations for spectroscopic constants of InH, InF, and InCl

Small- and medium-core pseudopotentials representing [Ar]3d10- and [Kr]-like cores, respectively, have been adjusted for the In atom, supplementing the energy-consistent three-valence-electron large-core ([Kr]4d10 core) pseudopotential of the Stuttgart group. The performance of these potentials is tested against those of other groups and against experiment, in calculations for the ground-state potential curves of InH, InF, and InCl, both at the self-consistent-field and correlated levels. The role of the core size is discussed, and systematic errors of large- and medium-core pseudopotentials are analyzed.

Images of the Response Signal of a 2D Gas of Carriers to a Pulsed Beam of 3D Phonons

The interaction of a 2D electron gas (2DEG) and a 2D hole gas (2DHG) with bulk acoustic phonons has been studied by different techniques in recent years (for a review cf. [1] and [2]). Due to the reduced dimensionality of a 2D gas of charge carriers (2DCG), the interaction with bulk phonons differs considerably from their interaction with 3DCGs. Another interesting feature of a 2DCG is the smallness of the Fermi wave vectors kF (and consequently the smallness of the Fermi momentum, the Fermi velocity υF , and the Fermi temperature TF). For a 2DCG the Fermi wave vector is comparable or even less than the typical wave vector of small energy acoustic phonons. Using phonon beams one can experimentally sweep relatively large volume of the 2D momentum space. There are very practical reasons for doing experiments of this type, because the electron-phonon interaction plays an important role in limiting the mobility, i.e. the performance of low-dimensional devices. Collisions with phonons limit the room temperature mobility of electrons in 2D high electron mobility transistors (HEMTs). In a series of papers (cf. [2]) Dietsche and collaboration (the Stuttgart group — SG) published the results of measurements of the time integrated response of a 2DEG to pulsed beams of acoustic phonons. In their experiments phonons propagated in a GaAs crystal and interacted with the 2D electrons lying in a {001} plane. They used sources of monochromatic phonons (a superconducting Al

Electron-phonon coupling in high temperature superconductors: The connection to superconducting behavior

Abstract The results of recent calculations of the frequency, linewidths, and coupling strengths to carriers on the Fermi surface for several phonons in La1.85Sr0.15CuO4 (LSCO) [our work] and YBa2Cu3O7 (YBCO) [by the Stuttgart group] are discussed and related to experiment. The estimates of the electron-phonon coupling constant are X = 1.35 for LSCO based on 11 phonons, and λ = 1.7 for YBCO based on 17 phonons. These coupling strengths are large enough to make the electron-phonon interaction a central feature in normal state transport properties and a likely candidate for the pairing mechanism for high temperature superconductivity. The strong coupling arises from features that are generic in the high temperature superconducting cuprates: a modest (certainly not large) density of states at the Fermi level which results in weak screening; a confinement of the metallic electrons to layers separated by dielectric regions, which further weakens screening and results in Madelung-like contributions to electron-phonon matrix elements; the site energies of the Cu d states and the O p states are roughly equal, leading to strong hybridization and highly metallic bands at the Fermi level.

Geodetic traverse in the venezuelan Andes; 1983 field campaign and first results

The traverse will be installed across the Andes mountains as a geodetic network ranging in elevation from 0 m at the Lake Maracaibo to 4400 m in the northern range. From the northern range, the network will descend down to the Llanos to an elevation of 300 m. The main part of the network covering the northern and the southern range has an area of about 20 km × 10 km. The northern and southern ranges are separated by the still-active Bocono Fault. The purpose of the geodetic traverse is to show, by two periods of measurements, variations of the geodetic parameters, caused by movements in the area of the Bocono Fault. After extensive preliminary investigations during the period 1980–1982, in the spring of 1983 the first field campaign, including the first measurements, was carried out. Participants in the campaign were the German groups from Hannover and Stuttgart, the Venezuelan group from the Universidad del Zulia, Maracaibo, and CIDA, Merida and IVIC from Caracas. The Stuttgart group was mainly occupied in observing the distances, directions and zenith angles in the network. At the same time, the Hannover group made the high-precision astronomic gravimetric measurements. All the observations were made in cooperation with the Venezuelan partners. From the autumn of 1983 to the spring of 1984, the first analysis was carried out. The Stuttgart group was responsible for the calculation of two- and three-dimensional coordinates of the points and the determination of local deflections of the vertical. By means of different models, it was also possible to calculate the effect of atmospheric refraction. The Hannover group took over the analysis of the astronomic gravimetric measurements. This paper deals mainly with the contribution of the Stuttgart group and its Venezuelan partners.

262. FSH and LH content of plasma after mitomycin treatment and the effect of the antibiotic on ovarian cellular constituents

The traverse will be installed across the Andes mountains as a geodetic network ranging in elevation from 0 m at the Lake Maracaibo to 4400 m in the northern range. From the northern range, the network will descend down to the Llanos to an elevation of 300 m. The main part of the network covering the northern and the southern range has an area of about 20 km × 10 km.The northern and southern ranges are separated by the still-active Bocono Fault. The purpose of the geodetic traverse is to show, by two periods of measurements, variations of the geodetic parameters, caused by movements in the area of the Bocono Fault. After extensive preliminary investigations during the period 1980–1982, in the spring of 1983 the first field campaign, including the first measurements, was carried out. Participants in the campaign were the German groups from Hannover and Stuttgart, the Venezuelan group from the Universidad del Zulia, Maracaibo, and CIDA, Merida and IVIC from Caracas.The Stuttgart group was mainly occupied in observing the distances, directions and zenith angles in the network. At the same time, the Hannover group made the high-precision astronomic gravimetric measurements. All the observations were made in cooperation with the Venezuelan partners. From the autumn of 1983 to the spring of 1984, the first analysis was carried out. The Stuttgart group was responsible for the calculation of two- and three-dimensional coordinates of the points and the determination of local deflections of the vertical. By means of different models, it was also possible to calculate the effect of atmospheric refraction. The Hannover group took over the analysis of the astronomic gravimetric measurements.This paper deals mainly with the contribution of the Stuttgart group and its Venezuelan partners.

265. Immunological induction of aspermatogenesis and increased steroidogenesis

The traverse will be installed across the Andes mountains as a geodetic network ranging in elevation from 0 m at the Lake Maracaibo to 4400 m in the northern range. From the northern range, the network will descend down to the Llanos to an elevation of 300 m. The main part of the network covering the northern and the southern range has an area of about 20 km × 10 km.The northern and southern ranges are separated by the still-active Bocono Fault. The purpose of the geodetic traverse is to show, by two periods of measurements, variations of the geodetic parameters, caused by movements in the area of the Bocono Fault. After extensive preliminary investigations during the period 1980–1982, in the spring of 1983 the first field campaign, including the first measurements, was carried out. Participants in the campaign were the German groups from Hannover and Stuttgart, the Venezuelan group from the Universidad del Zulia, Maracaibo, and CIDA, Merida and IVIC from Caracas.The Stuttgart group was mainly occupied in observing the distances, directions and zenith angles in the network. At the same time, the Hannover group made the high-precision astronomic gravimetric measurements. All the observations were made in cooperation with the Venezuelan partners. From the autumn of 1983 to the spring of 1984, the first analysis was carried out. The Stuttgart group was responsible for the calculation of two- and three-dimensional coordinates of the points and the determination of local deflections of the vertical. By means of different models, it was also possible to calculate the effect of atmospheric refraction. The Hannover group took over the analysis of the astronomic gravimetric measurements.This paper deals mainly with the contribution of the Stuttgart group and its Venezuelan partners.