FG Theoretische Chemie

25 Items

Recent Submissions
Activation of tetrafluoropropenes by rhodium(i) germyl and silyl complexes

Talavera, Maria ; Müller, Robert ; Ahrens, Theresia ; von Hahmann, Cortney N. ; Braun-Cula, Beatrice ; Kaupp, Martin ; Braun, Thomas (2019-09-20)

The reaction of the rhodium(I) complexes [Rh(E)(PEt3)3] (E = GePh3 (1), Si(OEt)3 (5)) with HFO-1234yf (2,3,3,3-tetrafluoropropene) afforded [Rh(F)(PEt3)3] (2) and the functionalized olefins Z-CF3CH[double bond, length as m-dash]CH(E) (E = GePh3 (4a), Si(OEt)3 (7)). Conceivable reaction pathways were assessed using DFT calculations. Reactions of [Rh(E)(PEt3)3] with HFO-1234ze (E-1,3,3,3-tetraflu...

Defect topologies in chiral liquid crystals confined to mesoscopic channels

Schlotthauer, Sergej ; Skutnik, Robert A. ; Stieger, Tillmann ; Schoen, Martin (2015-05-19)

We present Monte Carlo simulations in the grand canonical and canonical ensembles of a chiral liquid crystal confined to mesochannels of variable sizes and geometries. The mesochannels are taken to be quasi-infinite in one dimension but finite in the two other directions. Under thermodynamic conditions chosen and for a selected value of the chirality coupling constant, the bulk liquid crystal e...

The formation of biaxial nematic phases in binary mixtures of thermotropic liquid-crystals composed of uniaxial molecules

Skutnik, Robert A. ; Lehmann, Louis ; Püschel-Schlotthauer, Sergej ; Jackson, George ; Schoen, Martin (2019-04-08)

Monte Carlo simulations in the isothermal-isobaric ensemble are used to investigate the formation of an ordered, biaxial nematic phase in a binary mixture of thermotropic liquid crystals. The orientational dependence of the interaction between molecules of each pure component is the same as in the well-known Maier-Saupe model; each pure component of the mixture is therefore capable of forming a...

Hydrodynamic cavitation in Stokes flow of anisotropic fluids

Stieger, Tillmann ; Agha, Hakam ; Schoen, Martin ; Mazza, Marco G. ; Sengupta, Anupam (2017-05-30)

Cavitation, the nucleation of vapour in liquids, is ubiquitous in fluid dynamics, and is often implicated in a myriad of industrial and biomedical applications. Although extensively studied in isotropic liquids, corresponding investigations in anisotropic liquids are largely lacking. Here, by combining liquid crystal microfluidic experiments, nonequilibrium molecular dynamics simulations and th...

Mean-field density functional theory of a nanoconfined classical, three-dimensional Heisenberg fluid. II. The interplay between molecular packing and orientational order

Wandrei, Stefanie M. ; Roth, Roland ; Schoen, Martin (2018-08-03)

As in Paper I of this series of papers [S. M. Cattes et al., J. Chem. Phys. 144, 194704 (2016)], we study a Heisenberg fluid confined to a nanoscopic slit pore with smooth walls. The pore walls can either energetically discriminate specific orientations of the molecules next to them or are indifferent to molecular orientations. Unlike in Paper I, we employ a version of classical density functio...

Mean-field density functional theory of ananoconfined classical, three-dimensional Heisenberg fluid. I. The role of molecularanchoring

Cattes, Stefanie M. ; Gubbins, Keith E. ; Schoen, Martin (2016-05-17)

In this work, we employ classical density functional theory (DFT) to investigate for the first time equilibrium properties of a Heisenberg fluid confined to nanoscopic slit pores of variable width. Within DFT pair correlations are treated at modified mean-field level. We consider three types of walls: hard ones, where the fluid-wall potential becomes infinite upon molecular contact but vanishes...

A novel model for smectic liquid crystals: Elastic anisotropy and response to a steady-state flow

Püschel-Schlotthauer, Sergej ; Meiwes Turrión, Victor ; Stieger, Tillmann ; Grotjahn, Robin ; Hall, Carol K. ; Mazza, Marco G. ; Schoen, Martin (2016-10-25)

By means of a combination of equilibrium Monte Carlo and molecular dynamics simulations and nonequilibrium molecular dynamics we investigate the ordered, uniaxial phases (i.e., nematic and smectic A) of a model liquid crystal. We characterize equilibrium behavior through their diffusive behavior and elastic properties. As one approaches the equilibrium isotropic-nematic phase transition, diffus...

The effect of dilution and confinement on the behavior of the classical Heisenberg fluid

Wandrei, Stefanie Maria (2019)

In this work we present a classical density functional theory (DFT) study of the behavior of a classical three-dimensional “spin” fluid, the Heisenberg fluid. This model is the simplest model to describe a system with internal degrees of freedom, and can thus be used to describe the behavior of ferrofluids; fluids containing magnetic nanoparticles. Within the framework of DFT pair correlations ...

Investigating silica nanoparticles/polymer composites

Perrin, Elsa (2019)

Polymer / silica interface is investigated using coarse-grained molecular dynamics simulations. In particular, the different behavior of poly(acrylamide) (PAAm) and of poly(N,Ndimethylacrylamide) (PDMA) on the silica surface is compared. First, we show that the macroscopic behavior of PAAm and of PDMA are correctly represented by a model containing an explicit solvent. Then, the umbrella sampli...

Einfluß der Reaktionsenthalpie auf die Bildung von "Twisted Intramolecular Charge Transfer" (TICT) — Anregungszustände in unpolaren Lösungsmitteln: p-substituierte N,N-Dimethylaniline

Wermuth, Günter (1983)

In saturated hydrocarbons dual fluorescence appears both in p-N,N-Dimethylaminobenzonitrile (DMABN) and p-N,N-Dimethylaminoethylbenzoate (DMABEE). The temperaturedependence of the fluorescence quantum yield suggests that in DMABEE E(B*) ≈ E(TICT) and in DMABN E(B*) Smectic A1 — Smectic Ad Transition in Binary Mixtures of Compounds with Strongly Polar Terminal Groups

Bahr, Ch. ; Heppke, G. ; Shashidhar, R. (1985)

On the basis of high pressure studies we present here the evidence for the existence of a smectic A, — smectic Aj transition at high pressure in a binary liquid crystal mixture consisting of terminally polar compounds. A feature of this observation is that both the constituent compounds are three phenyl ring systems wherein the bridging dipoles are disposed additive with respect to the polar en...

Kerr Orientation Influence on Excited State Absorption Measurements

Menzel, Ralf ; Rapp, Werner (1986)

The possible influence of a strong nonresonant laser field on the orientation of dyes in solution is discussed as a potential source of measuring errors in excited state absorption analysis. The results of investigations on some typical samples suggest that, fortunately, the effect is very small.

Esters of (S)-1,2-propanediol and (R,R)-2,3-butanediol — Chiral Compounds Inducing Cholesteric Phases with a Helix Inversion ·

Heppke, G. ; Lötzsch, D. ; Oestreicher, F. (1987)

Mesogenic chiral esters of optically active (S)-1,2-propanediol and (R,R)-2,3-butanediol were synthesized. The compounds, added to a nematic phase induce cholesteric phases exhibiting a helix inversion with temperature variation. This effect is independent of the molecular structure of the nematic solvent. The inversion temperature varies only slightly with concentration but can be influenced b...

Fully relativistic calculations of EPR and paramagnetic NMR parameters for heavy atom compounds

Gohr, Sebastian (2018)

In the thesis at hand, a 4-component relativistic density functional theory (DFT) approach is applied within the ReSpect program package to calculations of magnetic resonance parameters for various open-shell systems containing heavy 4d and 5d transition metals. Such calculations represent a relatively uncharted territory. Therefore, the present work starts with a comprehensive benchmark study ...

Coarse-grained treatment of the self-assembly of colloids suspended in a nematic host phase

Püschel-Schlotthauer, Sergej ; Stieger, Tillmann ; Melle, Michael ; Mazza, Marco G. ; Schoen, Martin (2016)

The complex interplay of molecular scale effects, nonlinearities in the orientational field and long-range elastic forces makes liquid-crystal physics very challenging. A consistent way to extract information from the microscopic, molecular scale up to the meso- and macroscopic scale is still missing. Here, we develop a hybrid procedure that bridges this gap by combining extensive Monte Carlo (...

Synthesis, structure and bonding of hexaphenyl thorium(IV): observation of a non-octahedral structure

Pedrick, Elizabeth A. ; Hrobárik, Peter ; Seaman, Lani A. ; Wu, Guang ; Hayton, Trevor W. (2016)

We report herein the synthesis of the first structurally characterized homoleptic actinide aryl complexes, [Li(DME)(3)](2)[Th(C6H5)(6)] (1) and [Li(THF)(12-crown-4)](2)[Th(C6H5)(6)] (2), which feature an anion possessing a regular octahedral (1) or a severely distorted octahedral (2) geometry. The solid-state structure of 2 suggests the presence of pseudo-agostic ortho C-H center dot center dot...

Characterization of the [3Fe-4S](0/1+) cluster from the D14C variant of Pyrococcus furiosus ferredoxin via combined NRVS and DFT analyses

Lauterbach, Lars ; Gee, Leland B. ; Pelmenschikov, Vladimir ; Jenney, Francis E., Jr. ; Kamali, Saeed ; Yoda, Yoshitaka ; Adams, Michael W. W. ; Cramer, Stephen P. (2016)

The D14C variant of Pyrococcus furiosus ferredoxin provides an extraordinary framework to investigate a [3Fe-4S] cluster at two oxidation levels and compare the results to its physiologic [4Fe-4S] counterpart in the very same protein. Our spectroscopic and computational study reveals vibrational property changes related to the electronic and structural aspects of both Fe-S clusters.

Giant spin-orbit effects on H-1 and C-13 NMR shifts for uranium(VI) complexes revisited: role of the exchange-correlation response kernel, bonding analyses, and new predictions

Greif, Anja H. ; Hrobárik, Peter ; Autschbach, Jochen ; Kaupp, Martin (2016)

Previous relativistic quantum-chemical predictions of unusually large H-1 and C-13 NMR chemical shifts for ligand atoms directly bonded to a diamagnetic uranium(VI) center (P. Hrobarik, V. Hrobarikova, A. H. Greif and M. Kaupp, Angew. Chem., Int. Ed., 2012, 51, 10884) have been revisited by two- and four-component relativistic density functional methods. In particular, the effect of the exchang...

New approaches for the calibration of exchange-energy densities in local hybrid functionals

Maier, Toni M. ; Haasler, Matthias ; Arbuznikov, Alexey V. ; Kaupp, Martin (2016)

The ambiguity of exchange-energy densities is a fundamental challenge for the development of local hybrid functionals, or of other functionals based on a local mixing of exchange-energy densities. In this work, a systematic construction of semi-local calibration functions (CFs) for adjusting the exchange-energy densities in local hybrid functionals is provided, which directly links a given CF t...

The impact of substrate curvature on the self-assembly of liquid crystals

Püschel-Schlotthauer, Sergej (2017)

The interplay of anisotropic molecular interactions, nonlinearities of the orientational field, and long-range orientational correlations make the physics of liquid crystals both challenging and fascinating. Liquid crystals are known for their dual nature, i.e. a high degree of the orientational order combined with a certain degree of fluidity. The liquid-crystalline order can be enhanced, pert...