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Quantum Calculations (quantum + calculation)

Distribution by Scientific Domains

Physics and Astronomy	40%
Chemistry	40%

Selected Abstracts

Experimental and theoretical study of recovery mechanism of impurity effect by the addition of EDTA

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007
Y. Asakuma
Abstract The impurity effect by trivalent metal ion such as Al3+, Fe3+ and Cr3+ during crystal growth of KDP is reasonably well documented. If a metal ion is adsorbed onto the crystal surface, it prevents the step propagation relevant to the crystal growth rate. However, this impurity adsorption mechanism is still not well understood. Recently, in our work on the addition of chelate agents, a recovery effect of the metal ion adsorption was discovered. However, its recovery mechanism is not clearly understood both theoretically and phenomenally. In this research, ethylene-diamine-tetra-acetic acid, EDTA, which is the most common chelate agent, was used as a recovery agent. The recovery mechanism was considered from the correlation of experimental data and the interfacial distribution model that we proposed in our former study. Furthermore, quantum calculation of EDTA metal complex can explain the relaxation of impurity adsorption by the addition of EDTA. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

RAFT polymerization kinetics: How long are the cross-terminating oligomers?

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2009
Dominik Konkolewicz
Abstract We extend a new model for the kinetics of reversible addition-fragmentation chain transfer (RAFT) polymerization. The essence of this model is that the termination of the radical intermediate formed by the RAFT process occurs only with very short oligomeric radicals. In this work, we consider cross-termination of oligomers up to two monomers and an initiator fragment. This model accounts for the absence of three-armed stars in the molecular weight distribution, which are predicted by other cross-termination models, since the short third arm makes a negligible difference to the polymer's molecular weight. The model is tested against experiments on styrene mediated by cyano-isopropyl dithiobenzoate, and ESR experiments of the intermediate radical concentration. By comparing our model to experiments, we may determine the significance of cross-termination in RAFT kinetics. Our model suggests that to agree with the known data on RAFT kinetics, the majority of cross-terminating chains are dimeric or shorter. If longer chains are considered in cross-termination reactions, then significant discrepancies with the experiments (distinguishable star polymers in the molecular weight distribution) and quantum calculations will result. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3455,3466, 2009 [source]

Semi-classical calculation of resonant states of a charged particle interacting with a metallic surface

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2005
John Jairo Zuluaga
Abstract We assess the applicability of the semi-classical approach of Herman,Kluk with filter diagonalization to determine resonant states of either the electron-surface system or the ion-surface system. An effective potential model of the interaction of an electron with a ruthenium metallic surface is used. The evolution of the wave-function and the resonant states of this system are calculated. Analogous results for the interaction of the system formed by the H, and the ruthenium surface are presented. For the calculation of the resonances, the semi-classical wave-function is found, and the autocorrelation function between the initial and final wave-functions is calculated, from which the position and width of the resonances are extracted by using the harmonic inversion by filter diagonalization. The results are compared with results available in the literature for similar models obtained by quantum calculations using fast Fourier Transform. The positions of the lower-lying resonances found with the semi-classical and quantum approaches match closely, while the values of the widths of the resonances show larger discrepancies. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Antituberculosis Agents and an Inhibitor of the para -Aminobenzoic Acid Biosynthetic Pathway from Hydnocarpus anthelminthica Seeds

CHEMISTRY & BIODIVERSITY, Issue 8 2010
Jun-Feng Wang
Abstract Investigation on the extracts of Hydnocarpus anthelminthica seeds led to the isolation of three new compounds, anthelminthicins A,C (1,3, resp.), and two known ones, namely chaulmoogric acid (4) and ethyl chaulmoograte (5). Their structures were determined mainly by using spectroscopic techniques. The absolute configuration at the cyclopentenyl moiety of compound 2 was rationalized by quantum calculations. Base hydrolysis, followed by optical-rotation comparison, allowed assignment of the configuration of chaulmoogric-acid moiety of compounds 3 and 5. Biological assays revealed that compounds 1,5 significantly inhibit Mycobacterium tuberculosis (MTB) growth with MIC values of 5.54, 16.70, 4.38, 9.82, and 16.80,,M, respectively. Compound 3 was found to inhibit the pathway between chorismate and para -aminobenzoic acid (pAba) with a MIC value of 11.3,,M, representing a new example of pAba inhibitor isolated from a natural source. All compounds were not toxic to Candida albicans SC5314 at a concentration up to 100,,M. [source]

Prediction of phase equilibria for binary mixtures by molecular modeling

AICHE JOURNAL, Issue 10 2001
Maurizio Fermeglia
Two new procedures based on quantum/COSMO calculations and on molecular mechanics/dynamics simulations, respectively, for estimating the PHSCT EOS parameters and to predict VLE behavior for binary mixtures are presented. The quality of the predictions achieved with both methods, in conjunction with the confined computational time aspects involved, can be considered satisfactory so that these strategies can be judged as promising routes toward an on-line coupling between molecular and process simulation. [source]