A detailed analysis of the spin-crossover reaction of H2S binding to heme and the six-coordinated FeP(Im)-HS- porphyrin complex.

The potential energy surfaces of the H2S binding to iron-porphyrin (FeP) with the imidazole (Im) ligand via intersystem crossings are investigated by using density functional theory. The minimum energy intersystem crossing point (MEISCP) between the quintet and triplet states (MEISCPTQ) for the Fe(II)P(Im)-H2S complex is located at a Fe-S distance of 3.39 Šwith only 1.1 kcal/mol above the quintet state minimum. The second spin-crossover point, where a change from the triplet to the singlet state occurs, comes at a much shorter Fe-S distance of 2.79 Å, and the MEISCPST is located at 3.7 kcal/mol above the triplet state minimum. The nature of the chemical bonding along the Fe-S reaction coordinate from the ground state singlet to the quintet state along the path to the separated species is analyzed. An inspection of the vibrational modes reveals that the largest contribution to the triplet-quintet transition around the quintet and triplet state minimum comes from the symmetric shrinking of the pyrrole units of the porphyrin ring, indicating that the related reaction coordinate plays a main role in the intersystem crossing. The fully optimized structures of the Fe(II)P(Im)-HS- complex corresponding to three different spin multiplicities (M = 1, 3, 5) are characterized by a bent Fe-H-S conformation. The binding of the hydrosulfide anion to Fe(II)P(Im) in the quintet state induces a 0.2 Šdisplacement of the Fe atom out of the nitrogen porphyrin (Npyr) plane. The fully optimized structure of the ground state of Fe(II)P(Im)-HS- agrees well with experimental data for the corresponding heme models.

Modeling the hydrogen sulfide binding to heme.

The binding of hydrogen sulfide to a model heme compound is investigated by coupled-cluster singles-doubles augmented by a perturbative triple excitations, CCSD(T), and density functional theory, DFT. The minimum energy path for the H2S addition to an isolated heme center of the heme protein is evaluated by adopting as a model the heme compound FeP(Im) (P = porphyrin; Im = imidazole). The FeP(Im)-H2S aduct is bound by 13.7 kcal/mol at the CCSD(T) level of theory. Relaxed potential energy curves for the lowest lying spin states of the H2S to FeP(Im) binding using DFT reveal that the binding process is associated with a "double spin-crossover" reaction with the existence of long-distance van der Waals minima only 5-7 kcal/mol above the FeP(Im)-H2S ground state. The fact that the energy of the singlet ground state of FeP(Im)-H2S is so close in energy to the dissociation products FeP(Im) + H2S points towards the reversibility of the H2S adsorption/desorption process in biochemical reactions.

Spin-orbit effects in optical spectra of gold-silver trimers.

Cationic gold-silver trimers are ideal model systems for the evaluation of relativistic electronic structure theories. The closed-shell triangles allow one to test density functional and wavefunction-based methods in their prediction of optical properties, as dependent on composition and symmetry. Here we present the gas-phase optical spectra of AgNAu3-N+ (N = 0-3) clusters recorded by longitudinal photodissociation spectroscopy in the photon energy range 1.9-4.4 eV. The experimental data are compared to excited electronic state calculations in the framework of all-electron range-separated time-dependent density functional and equation-of-motion coupled cluster theory using two-component as well as the spin-free scalar relativistic theories. In particular, it is shown that for mixed trimers scalar-relativistic corrections are insufficient and a two-component approach becomes obligatory for a correct description of optical response properties including both spin-orbit coupling and charge-transfer effects.

The cohesive energy of superheavy element copernicium determined from accurate relativistic coupled-cluster theory.

The cohesive energy of bulk copernicium is accurately determined using the incremental method within a relativistic coupled-cluster approach. For the lowest energy structure of hexagonal close-packed (hcp) symmetry, we obtain a cohesive energy of -36.3 kJ mol-1 (inclusion of uncertainties leads to a lower bound of -39.6 kJ mol-1), in excellent agreement with the experimentally estimated sublimation enthalpy of -38 kJ mol-1 [R. Eichler et al., Angew. Chem. Int. Ed., 2008, 47, 3262]. At the coupled-cluster singles, doubles and perturbative triples level of theory, we find that the hcp structure is energetically quasi-degenerate with both face-centred and body-centred cubic structures. These results provide a basis for testing various density-functionals, of which the PBEsol functional yields a cohesive energy of -34.1 kJ mol-1 in good agreement with our coupled-cluster value.

Relativistic Coupled Cluster Calculations with Variational Quantum Electrodynamics Resolve the Discrepancy between Experiment and Theory Concerning the Electron Affinity and Ionization Potential of Gold.

The first ionization potential (IP) and electron affinity (EA) of the gold atom have been determined to an unprecedented accuracy using relativistic coupled cluster calculations up to the pentuple excitation level including the Breit and QED contributions. We reach meV accuracy (with respect to the experimental values) by carefully accounting for all individual contributions beyond the standard relativistic coupled cluster approach. Thus, we are able to resolve the long-standing discrepancy between experimental and theoretical IP and EA of gold.

[Satisfaction of patients with tracheostomal epithesis]. / Die Tracheostomaepithese - eine Evaluation der Patientenzufriedenheit.

BACKGROUND: The utilization of craniofacial prosthesis has proven to be very successful for craniofacial defects. However, there is a lack of knowledge about the value of an epithesis for voice rehabilitation in patients with tracheostomy. The aim of this study was to describe application of the tracheostomy epithesis and to present a systematic analysis of the functional results of this prosthetic technique. MATERIALS AND METHODS: This retrospective analysis included 48 patients on follow-up being treated in three different centers after laryngectomy and/or tracheostomy between 2008 and 2014. Subjects were given a questionnaire with items such as speech quality, quality of life, free hand speech ability, respiratory quality and sufficient tracheostomal sealing comparing values before and after application of an individually custom-made tracheostomy epithesis. Twenty-eight answered the questionnaire and could be reported. RESULTS: Twenty-eight of 48 patients were consistently being included in follow-up. The statistical analysis revealed a significant improvement of tracheostoma occlusion (p < 0.05) and improvement in free hand speech ability (p < 0.05). A leakage of air during voice production could be prevented in 59.3% after application of an epithesis. Quality of life correlated directly with successful utilization of an epithesis. CONCLUSION: In the literature, different industrialized products are described to realize occlusion of the tracheostoma for sufficient speech production without using the hands. In numerous cases commercial solutions fail and the patients need individual modifications. Our study first describes the evaluation of custom-made tracheostomal epithesis. From our observed results we advocate the individual tracheostomal epithesis as a durable solution for voice rehabilitation.

Influence of spin-orbit effects on structures and dielectric properties of neutral lead clusters.

Combining molecular beam electric deflection experiments and global optimization techniques has proven to be a powerful tool for resolving equilibrium structures of neutral metal and semiconductor clusters. Herein, we present electric molecular beam deflection experiments on PbN (N = 7-18) clusters. Promising structures are generated using the unbiased Birmingham Cluster Genetic Algorithm approach based on density functional theory. The structures are further relaxed within the framework of two-component density functional theory taking scalar relativistic and spin orbit effects into account. Quantum chemical results are used to model electric molecular beam deflection profiles based on molecular dynamics calculations. Comparison of measured and simulated beam profiles allows the assignment of equilibrium structures for the most cluster sizes in the examined range for the first time. Neutral lead clusters adopt mainly spherical geometries and resemble the structures of lead cluster cations apart from Pb10. Their growth pattern deviates strongly from the one observed for tin and germanium clusters.

Can an ab initio three-body virial equation describe the mercury gas phase?

We report a sixth-order ab initio virial equation of state (EOS) for mercury. The virial coefficients were determined in the temperature range from 500 to 7750 K using a three-body approximation to the N-body interaction potential. The underlying two-body and three-body potentials were fitted to highly accurate Coupled-Cluster interaction energies of Hg2 (Pahl, E.; Figgen, D.; Thierfelder, C.; Peterson, K. A.; Calvo, F.; Schwerdtfeger, P. J. Chem. Phys. 2010, 132, 114301-1) and equilateral-triangular configurations of Hg3. We find the virial coefficients of order four and higher to be negative and to have large absolute values over the entire temperature range considered. The validity of our three-body, sixth-order EOS seems to be limited to small densities of about 1.5 g cm(-3) and somewhat higher densities at higher temperatures. Termwise analysis and comparison to experimental gas-phase data suggest a small convergence radius of the virial EOS itself as well as a failure of the three-body interaction model (i.e., poor convergence of the many-body expansion for mercury). We conjecture that the nth-order term of the virial EOS is to be evaluated from the full n-body interaction potential for a quantitative picture. Consequently, an ab initio three-body virial equation cannot describe the mercury gas phase.

The predicted spectrum and singlet-triplet interaction of the hypermetallic molecule SrOSr.

In accordance with previous studies in our group on Be, Mg, and Ca hypermetallic oxides, we find that SrOSr has a linear X̃1Σ(g)+ ground electronic state and a very low lying first excited ã3Σ(u)+ triplet electronic state. No gas-phase spectrum of this molecule has been assigned yet, and to encourage and assist in its discovery we present a complete ab initio simulation, with absolute intensities, of the infrared absorption spectrum for both electronic states. The three-dimensional potential energy surfaces and the electric dipole moment surfaces of the X̃1Σ(g)+ and ã3Σ(u)+ electronic states are calculated using a multireference configuration interaction (MRCISD) approach in combination with internally contracted multireference perturbation theory (RS2C) based on complete active space self-consistent field (CASSCF) wave functions applying a Sadlej pVTZ basis set for both O and Sr and the Stuttgart relativistic small-core effective core potential for Sr. The infrared spectra are simulated using the MORBID program system. We also calculate vertical excitation energies and transition moments for several excited singlet and triplet electronic states in order to predict the positions and intensities of the most prominent singlet and triplet electronic absorption bands. Finally, for this heavy molecule, we calculate the singlet­triplet interaction matrix elements between close-lying vibronic levels of the X̃ and ã electronic states and find them to be very small.

A comparative density functional study of the high-pressure phases of solid ZnX, CdX, and HgX (X = S, Se, and Te): trends and relativistic effects.

The pressure dependence of bulk properties for the group 12 chalcogenides MX (M = Zn, Cd, Hg; X = S, Se, Te) from density functional theory are presented. Energy-volume and corresponding enthalpy-pressure relationships are determined to obtain the transition paths and properties of various high-pressure phases. The influence of relativistic effects is discussed with the aim to explain the unique behavior of the mercury chalcogenides as compared to the lighter zinc and cadmium homologs at high pressures. The neglect of relativistic effects leads to a more CdX like behavior of the mercury chalcogenides, and the pronounced change in coordination of the cinnabar phase at high pressures is due to relativistic effects.

A comparative density functional study of the low pressure phases of solid ZnX, CdX, and HgX: trends and relativistic effects.

A comprehensive density functional study of the group 12 chalcogenides has been carried out to study the impact of relativistic effects on the solid-state and electronic structure of the mercury chalcogenides in order to explain their unique behavior compared to the lighter group 12 congeners. For this, we present scalar-relativistic and nonrelativistic density functional calculations for several crystal structures commonly occurring in ZnX, CdX, and HgX (X = S, Se, and Te). The cohesive energies and other ground-state properties (at the zero-temperature limit) are obtained to identify the low-pressure phases and to discuss relativistic effects. Relativistic crucially influences the crystal structure in HgS, an effect less pronounced in the heavier chalcogenides HgSe and HgTe. However, for HgSe and HgTe we find that relativistic effects have a major impact on the electronic structure, where the change upon neglect of relativity goes as far as to the restoration of semiconducting properties.

Diatomics-in-Molecules Modeling of Many-Body Effects on the Structure and Thermodynamics of Mercury Clusters.

The stable structures and melting behavior of Hgn clusters, 2 ≤ n < 60, have been theoretically investigated using an updated diatomics-in-molecules (DIM) model initially proposed by Kitamura [Chem. Phys. Lett.2006, 425, 2056]. Global optimization and sampling at finite temperature are achieved on the basis of hierarchical and nested Markov chain Monte Carlo methods, respectively. The DIM model predicts highly symmetric icosahedral global minima that are generally similar to the standard van der Waals atomic clusters, without any indication of distorted or low-coordinated geometries, but also at variance with the global minima found with the pairwise Hg2 potential. The combined influences of surface and many-body effects due to s-p mixing are considerable on the melting point: although the model predicts a bulk melting temperature in fair agreement with experimental results, it is found to decrease with increasing cluster size.

The predicted spectrum of the hypermetallic molecule MgOMg.

The present study of MgOMg is a continuation of our theoretical work on Group 2 M(2)O hypermetallic oxides. Previous ab initio calculations have shown that MgOMg has a linear (1)Σ(g)+ ground electronic state and a very low lying first excited triplet electronic state that is also linear; the triplet state has (3)Σ(u)+ symmetry. No gas phase spectrum of this molecule has been assigned, and here we simulate the infrared absorption spectrum for both states. We calculate the three-dimensional potential energy surface, and the electric dipole moment surfaces, of each of the two states using a multireference configuration interaction (MRCISD) approach based on full-valence complete active space self-consistent field (FV-CASSCF) wavefunctions with a cc-pCVQZ basis set. A variational MORBID calculation using our potential energy and dipole moment surfaces is performed to determine rovibrational term values and to simulate the infrared absorption spectrum of the two states. We also calculate the dipole polarizability of both states at their equilibrium geometry in order to assist in the interpretation of future beam deflection experiments. Finally, in order to assist in the analysis of the electronic spectrum, we calculate the vertical excitation energies, and electric dipole transition matrix elements, for six excited singlet states and five excited triplet states using the state-average full valence CASSCF-MRCISD/aug-cc-pCVQZ procedure.

The unusual solid-state structure of mercury oxide: relativistic density functional calculations for the group 12 oxides ZnO, CdO, and HgO.

The solid-state structure of mercury oxide and its low-pressure modifications are known to significantly differ from those found for the corresponding zinc and cadmium compounds, that is, one changes from a simple hexagonal wurtzite or cubic rock salt structure found in zinc oxide and cadmium oxide to unusual chainlike montroydite and cinnabar structures in mercury oxide. Here, we present relativistic and nonrelativistic density functional studies which demonstrate that this marked structural difference is caused by relativistic effects. For HgO, the simple rock salt structure is only accessible at higher pressures. Relativistic effects reduce the cohesive energy by 2.2 eV per HgO unit and decrease the density of the crystal by 14% due to a change in the crystal symmetry. Band structure and density of states calculations also reveal large changes in the electronic structure due to relativistic effects, and we argue that the unusual yellow to red color of HgO is a relativistic effect as well.

Resolving the optical spectrum of water: coordination and electrostatic effects.

The optical absorption of small water clusters, water chains, liquid water, and crystalline ice is analyzed computationally. We identify two competing mechanisms determining the onset of the optical absorption: Electronic transitions involving surface molecules of finite clusters or chains cause a redshift upon molecular aggregation compared to monomers. On the other hand, a strong blueshift is caused by the electrostatic environment experienced by water monomers embedded in a hydrate shell. Concerning the recent dispute over the structure of the liquid, the present results support the conventional fourfold coordinated water, as obtained from ab initio molecular-dynamics simulations.

[Guideline for therapy of malignant thyroid tumours: pleading for an actualization]. / Leitlinie zur Therapie maligner Schilddrüsentumoren: Plädoyer für eine Aktualisierung.

Total (or near total) thyroidectomy (TE) followed by radioiodine ((131)I) ablation (RIA) of residual thyroid tissue is considered to be the ideal treatment for differentiated thyroid carcinoma. However, the actual guideline of the DGN (German Society of Nuclear Medicine) recommends for the so-called papillary micro-carcinoma of the thyroid (PMC) no further therapeutic strategy (no complete TE, no (131)I-ablation of the remaining lobe). PMC has been defined as papillary carcinoma measuring 1 cm (T1) in maximal diameter according to the World Health Organization classification system for thyroid tumours (1988). The new WHO-classification (starting in 2003) defines the T1-tumour measuring 2 cm in maximal diameter. The authors demand a new, modern guideline, following the new WHO classification. This includes, that despite the overall excellent prognosis for patients with PMC, the treatment of patients with T1-tumours of the new WHO-classification (including the "old" PMC) should be no different from the treatment of patients with conventional papillary thyroid carcinoma, i.e. complete surgery (TE and central lymph node dissection) followed by RIA of residual thyroid tissue. The authors argue that it is not appropriate to consider the tumour size as the single most important key factor for therapy and prognosis. Even small tumours may have poor prognostic factors, such as lymph node metastasis, multifocality or molecular characteristics (expression of oncogenes).

Dependence of relativistic effects on electronic configuration in the neutral atoms of d- and f-block elements.

Although most neutral d- and f-block atoms have nd(g-2)(n + 1)s(2) and (n - 1)f(g-2)(n + 1)s(2) ground configurations, respectively, where g is the group number (i.e., number of valence electrons), one-third of these 63 atoms prefer a higher d-population, namely via (n + 1)s-->nd "outer" to "inner" electron shift (particularly atoms from the second d-row), or via (n - 1)f-->nd "inner" to "outer" electron shift (particularly atoms from the second f-row). Although the response to the modified self-consistent field is orbital destabilization and expansion for (n + 1)s-->nd, and stabilization and contraction for (n - 1)f-->nd, the relativistic modification of the valence orbital responses is stabilization in both cases. This is explained by double perturbation theory. Accordingly, electron configuration and relativity trigger the orbital energies, the orbital populations and the chemical shell effects in different ways. The particularly pronounced relativistic effects in groups 10 and 11, the so-called gold maximum, occur because of particularly efficient cooperative nonrelativistic shell effects and relativistic stabilization effects (inverse indirect effect) at the end of the d-block.

The stability of gold iodides in the gas phase and the solid state.

The stability of gold iodides in the oxidation state +I and +III is investigated at the ab initio and density functional level using relativistic and nonrelativistic energy-adjusted pseudopotentials for gold and iodine. The calculations reveal that relativistic effects stabilize the higher oxidation state of gold as expected, that is Au2I6 is thermodynamically stable at the relativistic level, whilst at the nonrelativistic level the complex of two iodine molecules weakly bound to both gold atoms in Au2I2 is energetically preferred. The rather low stability of AuI3 with respect to dissociation into AuI and I2 will make it difficult to isolate this species in the solid state as (possibly) Au2I6 or detect it by matrix-isolation techniques. The monomer AuI3 is Jahn-Teller distorted from the ideal trigonal planar (D3h) form, but adopts a Y-shaped structure (in contrast to AuF3 and AuCl3), and in the nonrelativistic case can be described as I2 weakly bound to AuI. Relativistic effects turn AuI3 from a static Jahn-Teller system to a dynamic one. For the yet undetected gas-phase species AuI accurate coupled-cluster calculations for the potential energy curve are used to predict vibrational-rotational constants. Solid-state density functional calculations are performed for AuI and Au2I6 in order to predict cohesive energies.

Nuclear quadrupole moment of 57Fe from microscopic nuclear and atomic calculations.

The nuclear quadrupole moment (NQM) of the Ipi = 3/2(-) excited nuclear state of 57Fe at 14.41 keV, important in Mössbauer spectroscopy, is determined from the large-scale nuclear shell-model calculations for 54Fe, 57Fe, and also from the electronic ab initio and density functional theory calculations including solid state and electron correlation effects for the molecules Fe(CO)(5) and Fe(C5H5)(2). Both independent methods yield very similar results. The recommended value is 0.15(2) e b. The NQM of the isomeric 10+ in 54Fe has also been calculated. The new NQM values for 54Fe and 57Fe are consistent with the perturbed angular distribution data.

Structure and electron affinity of platinum fluorides.

The structure, stability, and electron affinity of the even numbered molecular platinum fluorides PtF(2)(n) (n = 1-4) were studied by scalar relativistic density functional and coupled cluster methods. The di, tetra, and hexafluorides possess triplet ground states, while PtF(8) is a singlet. Formation of the latter from PtF(6) and F(2) is found to be endothermic. Differences between adiabiatic and vertical electron affinities are only significant for PtF(2).