intermixing in heteroepitaxial islands fast self consistent calculation of the concentration profile minimizing the elastic energy

We present a novel computational method for finding the concentra- tion profile which minimizes the elastic energy stored in heteroepitaxial islands. Based on a suitable combination of continuum elasticity theory and configura- tional Monte Carlo, we show that such profiles can be readily found by a simple, yet fully self-consistent, iterative procedure. We apply the method to SiGe/Si islands, considering realistic three-dimensional shapes (pyramids, domes and barns), finding strongly non-uniform distributions of Si and Ge atoms, in qualitative agreement with several experiments. Moreover, our simulated selective-etching profiles display, in some cases, a remarkable resemblance to the experimental ones, opening intriguing questions on the interplay between kinetic, entropic and elastic effects

A computational study of the ClOO and OClO radicals

Structure, energetics and vibrations of the ClOO and OClO radicals are treated ab initio in the 6-31G* basis set with the MP2 correlation corrections. The energetics is refined at the MP4 level. In all treatments the ClOO isomer exhibits lower energy. The smallest calculated energy separation between both structures equals 16 kJ/mol. A good agreement with available experimental data has been found

C

The five isolated-pentagon-rule (IPR) satisfying isomers of C78, labeled 1-5, or according to symmetry as D3, $C_{2v}$, $C'_{2v}$, $D_{3h}$, and $D'_{3h}$, are computed. The cage geometries are optimized at the ab initio HF level with the standard 3-21G basis set (HF/3-21G). The separation energetics is then computed using the B3LYP density-functional treatment in the standard 6-31G* basis set (B3LYP/6-31G*//HF/3-21G). Harmonic vibrational frequencies are calculated by the SAM1 semiempirical method. The computed energies, structural and vibrational data are employed in the construction of isomeric partition functions and evaluation of the relative Gibbs free energies. The results are converted into relative concentrations for a wide temperature interval. The $C'_{2v}$ structure is the most populated throughout while the $D_{3h}$ species is negligible at all temperatures. The agreement between theory and experiment is reasonable, though some aspects are still to be clarified

H2O·HF@C70: Encapsulation Energetics and Thermodynamics

This report deals with the quantum-chemical evaluation of the energetics and thermodynamics of the simultaneous encapsulation of HF and H (Formula presented.) O by the IPR (isolated pentagon rule) C (Formula presented.) fullerene cage, yielding (Formula presented.) species which were synthesized and characterized recently, thus further expanding the family of fullerene endohedrals with non-metallic encapsulates. The structures were optimized at the DFT (density functional theory) M06-2X/6-31++G** level. The encapsulation energetics were further refined by the advanced B2PLYPD/6-31++G** and B2PLYPD/6-311++G** methods. After enhancement of the B2PLYPD/6-311++G** encapsulation energy for the BSSE and steric corrections, the encapsulation energy gain was obtained, as 26 kcal/mol. The equilibrium encapsulation thermodynamics were described using the M06-2X/6-31++G** partition functions. The results correspond to our previous evaluations for the water dimer encapsulation by C (Formula presented.) cages. © 2023 by the authors.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Double-exponential decay of orientational correlations in semiflexible polyelectrolytes

In this paper we revisited the problem of persistence length of polyelectrolytes. We performed a series of Molecular Dynamics simulations using the Debye-Hückel approximation for electrostatics to test several equations which go beyond the classical description of Odijk, Skolnick and Fixman (OSF). The data confirm earlier observations that in the limit of large contour separations the decay of orientational correlations can be described by a single-exponential function and the decay length can be described by the OSF relation. However, at short countour separations the behaviour is more complex. Recent equations which introduce more complicated expressions and an additional length scale could describe the results very well on both the short and the long length scale. The equation of Manghi and Netz when used without adjustable parameters could capture the qualitative trend but deviated in a quantitative comparison. Better quantitative agreement within the estimated error could be obtained using three equations with one adjustable parameter: 1) the equation of Manghi and Netz; 2) the equation proposed by us in this paper; 3) the equation proposed by Cannavacciuolo and Pedersen. Two characteristic length scales can be identified in the data: the intrinsic or bare persistence length and the electrostatic persistence length. All three equations use a single parameter to describe a smooth crossover from the short-range behaviour dominated by the intrinsic stiffness of the chain to the long-range OSF-like behaviour

Calculated Equilibrium Populations of Ti2C2@C82 Isomers

High-temperature equilibrium relative populations of two Ti2C2@C82 isomers isolated recently are treated by quantum-chemical calculations, viz. endohedrals with the C s (c);6-C82 and C 3v (b);8-C82 IPR (isolated-pentagon-rule) cages. The calculations are carried out using the Gibbs energy based on the MP2=FU/6-31+G*∼SDD energetics and B3LYP/6-31G*∼SDD entropy. The observed ratio Ti2C2@C s (c);6-C82 : Ti2C2@C 3v (b);8-C82=1.6:1 is in the computations obtained at a temperature of 1543 K, i.e., in the supposed synthetic temperature region. Before that point, the two isomers reach their equimolarity at a temperature of 983 K. This fine theory-experiment agreement represents another example of a good performance of the Gibbs-energy based quantum-chemical evaluations of the fullerenic equilibrium compositions under the high-temperature synthetic conditions. © 2023 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing LimitedOpen access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]