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Stretchable electronic conductors are vital components in soft robotics and flexible electronics. One method for producing these is combining conductive filler with a nonconductive elastomer. These composites commonly exhibit significant piezoresistivity. This work examines various mechanisms that may underlie this effect. These composites are generally analyzed through percolation theory, which describes the nonlinear relationship between filler volume fraction and conductivity. However, it is unclear whether percolation theory can explain their piezoresistivity or whether mechanisms such as rearrangement of the conductive network under deformation must be considered. This work compares volumetric change in the context of percolation theory against network rearrangement to examine the relative significance of these factors in determining piezoresistivity. Digital image correlation is utilized to investigate volumetric changes in carbon‐black silicone composites and finds that the typical assumption of incompressibility is reasonable, suggesting that volumetric changes alone cannot account for the behavior. A computational model is also developed, which implies that network rearrangement is likely a more significant factor and that interparticle interactions are crucial in understanding this effect. It was found that the most realistic modeling results were achieved only when both rigid and attractive interparticle interactions were accounted for in the model. [ABSTRACT FROM AUTHOR]

The melting of argon clusters ArN is investigated by applying a parallel-tempering Monte Carlo algorithm for all cluster sizes in the range from 55 to 309 atoms. Extrapolation to the bulk gives a melting temperature of 85.9 K in good agreement with the previous value of 88.9 K using only Mackay icosahedral clusters for the extrapolation [E. Pahl, F. Calvo, L. Koči, and P. Schwerdtfeger, "Accurate melting temperatures for neon and argon from ab initio Monte Carlo simulations," Angew. Chem., Int. Ed. 47, 8207 (2008)]. Our results for argon demonstrate that for the extrapolation to the bulk one does not have to restrict to magic number cluster sizes in order to obtain good estimates for the bulk melting temperature. However, the extrapolation to the bulk remains a problem, especially for the systematic selection of suitable cluster sizes. [ABSTRACT FROM AUTHOR]

Second, third, and fourth thermal and acoustic virial coefficients between 100 and 1000 K are computed for different argon interaction models derived from combinations of accurate two- and three-body potentials. Differences between the various interaction models tested mirror the presumed order in the accuracy of these models, but are not well captured at the level of the lowest-order contributions in the virial expansion: While the second- and third-order virial coefficients are found to be rather insensitive to small variations in the two- and three-body potentials, more pronounced differences in higher-order coefficients are currently of limited use in assessing the accuracy of the interaction potential due to difficulties in the unambiguous experimental determination of these higher-order coefficients. In contrast, pressure-volume and speed-of-sound data - both of which are experimentally known to highest accuracies - are found to be insensitive to small variations in the interaction model. All but the least accurate models reproduce experimental pressure-volume and speed-of-sound data near-quantitatively in regions where the (fourth-order) virial expansions apply. All quantities considered are found to be completely unaffected by a non-vanishing quadruple-dipole four-body potential. [ABSTRACT FROM AUTHOR]

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 ΔT 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+ΔT data. The Hg2 potential curves yield dissociation energies of De=424/392 cm-1 and equilibrium distances of re=3.650/3.679 Å at the CBS/CCSD(T)+SO and CBS/CCSD(T)+SO+ΔT 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 De=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. [ABSTRACT FROM AUTHOR]

The frozen local hole approximation (FLHA) is an adiabatic approximation which is aimed to simplify the correlation calculations of valence and conduction bands of solids and polymers or, more generally, of the ionization potentials and electron affinities of any large system. Within this approximation correlated local hole states (CLHSs) are explicitly generated by correlating local Hartree-Fock (HF) hole states, i.e., (N-1)-particle determinants in which the electron has been removed from a local occupied orbital. The hole orbital and its occupancy are kept frozen during these correlation calculations, implying a rather stringent configuration selection. Effective Hamilton matrix elements are then evaluated with the above CLHSs; diagonalization finally yields the desired correlation corrections for the cationic hole states. We compare and analyze the results of the FLHA with the results of a full multireference configuration interaction with single and double excitations calculation for two prototype model systems, (H2)n ladders and H–(Be)n–H chains. Excellent numerical agreement between the two approaches is found. Comparing the FLHA with a full correlation treatment in the framework of quasidegenerate variational perturbation theory reveals that the leading contributions in the two approaches are identical. In the same way it could be shown that a much less demanding self-consistent field (SCF) calculation around a frozen local hole fully recovers, up to first order, all the leading single excitation contributions. Thus, both the FLHA and the above SCF approximation are well justified and provide a very promising and efficient alternative to fully correlated wave-function-based treatments of the valence and conduction bands in extended systems. [ABSTRACT FROM AUTHOR]

An accurate potential energy curve has been derived for the xenon dimer using state-of-the-art relativistic coupled-cluster theory up to quadruple excitations accounting for both basis set superposition and incompleteness errors. The data obtained is fitted to a computationally efficient extended Lennard-Jones potential form and to a modified Tang–Toennies potential function treating the short- and long-range part separately. The vibrational spectrum of Xe2obtained from a numerical solution of the rovibrational Schrödinger equation and subsequently derived spectroscopic constants are in excellent agreement with experimental values. We further present solid-state calculations for xenon using a static many-body expansion up to fourth-order in the xenon interaction potential including dynamic effects within the Einstein approximation. Again we find very good agreement with the experimental (face-centred cubic) lattice constant and cohesive energy. [ABSTRACT FROM PUBLISHER]

State-of-the-art relativistic coupled-cluster theory is used to construct many-body potentials for the noble-gas element radon to determine its bulk properties including the solid-to-liquid phase transition from parallel tempering Monte Carlo simulations through either direct sampling of the bulk or from a finite cluster approach. The calculated melting temperature are 200(3) K and 200(6) K from bulk simulations and from extrapolation of finite cluster values, respectively. This is in excellent agreement with the often debated (but widely cited) and only available value of 202 K, dating back to measurements by Gray and Ramsay in 1909., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The cohesive energies of argon in its cubic and hexagonal closed packed structures are computed with an unprecedented accuracy of about 5 J mol(-1) (corresponding to 0.05 % of the total cohesive energy). The same relative accuracy with respect to experimental data is also found for the face-centered cubic lattice constant deviating by ca. 0.003 Å. This level of accuracy was enabled by using high-level theoretical, wave-function-based methods within a many-body decomposition of the interaction energy. Static contributions of two-, three-, and four-body fragments of the crystal are all individually converged to sub-J mol(-1) accuracy and complemented by harmonic and anharmonic vibrational corrections. Computational chemistry is thus achieving or even surpassing experimental accuracy for the solid-state rare gases., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An old problem solved: Monte Carlo simulations using the diatomic-in-molecule method derived from accurate ground- and excited-state relativistic calculations for Hg2 show that the melting temperature for bulk mercury is lowered by 105 K, which is due to relativistic effects., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)