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Tilo Söhnel

Publications and source records attributed to Tilo Söhnel.

7 recordsLinked to original sources
PubMed2005

Ground-state properties and static dipole polarizabilities of the alkali dimers from K2 n to Fr2 n(n=0,+1) from scalar relativistic pseudopotential coupled cluster and density functional studies.

The newly adjusted energy-consistent nine-valence-electron pseudopotentials for K to Fr are used to calculate spectroscopic properties for the neutral and positively charged alkali dimers using coupled cluster and density functional theory. For the neutral dimers the static dipole polarizability was calculated. The coupled cluster results are all in excellent agreement with experimental values. The density functionals used can give quite different spectroscopic properties especially for the dipole polarizability, with the Perdew-Wang PW91 functional performing best.

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PubMed2005

The quadrupole moment of the 3/2+ nuclear ground state of 197Au from electric field gradient relativistic coupled cluster and density-functional theory of small molecules and the solid state.

An attempt is made to improve the currently accepted muonic value for the 197Au nuclear quadrupole moment [+0.547(16)x10(-28) m2] for the 3/2+ nuclear ground state obtained by Powers et al. [Nucl. Phys. A230, 413 (1974)]. From both measured Mossbauer electric quadrupole splittings and solid-state density-functional calculations for a large number of gold compounds a nuclear quadrupole moment of +0.60x10(-28) m2 is obtained. Recent Fourier transform microwave measurements for gas-phase AuF, AuCl, AuBr, and AuI give accurate bond distances and nuclear quadrupole coupling constants for the 197Au isotope. However, four-component relativistic density-functional calculations for these molecules yield unreliable results for the 197Au nuclear quadrupole moment. Relativistic singles-doubles coupled cluster calculations including perturbative triples [CCSD(T) level of theory] for these diatomic systems are also inaccurate because of large cancellation effects between different field gradient contributions subsequently leading to very small field gradients. Here one needs very large basis sets and has to go beyond the standard CCSD(T) procedure to obtain any reliable field gradients for gold. From recent microwave experiments by Gerry and co-workers [Inorg. Chem. 40, 6123 (2001)] a significantly enhanced (197)Au nuclear quadrupole coupling constant in (CO)AuF compared to free AuF is observed. Here, these cancellation effects are less important, and relativistic CCSD(T) calculations finally give a nuclear quadrupole moment of +0.64x10(-28) m2 for 197Au. It is argued that it is currently very difficult to improve on the already published muonic value for the 197Au nuclear quadrupole moment.

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PubMed2005

Solid state density functional calculations for the group 11 monohalides.

The group 11 monohalides are characterized by a variety of different solid-state structures and modifications. The copper halides crystallize mainly in a cubic zinc blende structure, while silver halides are mostly found in a rock salt modification. Completely different are the gold compounds where relativistic effects change the symmetry from a cubic to a chainlike AuX arrangement (X = F, Cl, Br, I) with short Au-Au internuclear distances. Here we present a systematic study of all solid state group 11 halides by scalar relativistic density functional theory for the experimentally known and observed structures, as well as for other unknown modifications and compare their relative stability.

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PubMed2003

LaSeTe2-temperature dependent structure investigation and electron holography on a charge-density-wave-hosting compound.

Single crystals of LaSeTe(2) have been prepared by reaction of the elements in a LiCl/RbCl flux at 970 K for seven days. Satellite reflections observed in diffraction experiments indicate the presence of an incommensurate lattice distortion, which is of the charge-density-wave (CDW) type. The modulated structure has been solved from X-ray data at 173, 293, and 373 K. LaSeTe(2) crystallizes in the 3+1-dimensional orthorhombic superspace group Cmcm(00gamma)s00 (No. 63.2) with lattice parameters of a=4.295(1), b=25.371(4), c=4.306(1) A (173 K), a=4.297(1), b=25.408(4), c=4.309(1) A (293 K), and a=4.309(1), b=25.481(6), c=4.321(1) A (373 K). The modulation vector q=(0, 0, 0.288) does not change over the temperature interval. Electron holographic investigations confirm the existence of the modulation and help to visualize the charge-density wave.

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PubMed2002

Properties of small- to medium-sized mercury clusters from a combined ab initio, density-functional, and simulated-annealing study.

Relativistic coupled-cluster and second-order many-body perturbation theories were used to construct two- and three-body potentials for the interaction between mercury atoms. A subsequent combined simulated-annealing downhill simplex and conjugate gradient-optimization procedure gave global minima for mercury clusters with up to 30 atoms. The calculations reveal magic cluster numbers of 6, 13, 19, 23, 26, and 29 atoms. At these cluster sizes, the static dipole polarizability obtained from density-functional theory has a minimum. The calculations also reveal a fast convergence of the polarizability towards the bulk limit in contrast to the singlet-triplet gap or the ionization potential.

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