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Dispersion Interactions (dispersion + interaction)
Selected AbstractsDispersion interactions in density-functional theoryJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2009Erin R. Johnson Abstract Density-functional theory (DFT) allows for the calculation of many chemical properties with relative ease, thus making it extremely useful for the physical organic chemistry community to understand and focus on various experiments. However, density-functional techniques have their limitations, including the ability to satisfactorily describe dispersion interactions. Given the ubiquitous nature of dispersion in chemical and biological systems, this is not a trivial matter. Recent advances in the development of DFT methods can treat dispersion. These include dispersion-corrected DFT (using explicit, attractive dispersion terms), parameterized functionals, and dispersion-correcting potentials, all of which can dramatically improve performance for dispersion-bound species. In this perspective, we highlight the achievements made in modeling dispersion using DFT. We hope that this will provide valuable insight to both computational chemists and experimentalists, who aim to study physical processes driven by dispersion interactions. Copyright © 2009 John Wiley & Sons, Ltd. [source] A new parallel algorithm of MP2 energy calculationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2006Kazuya Ishimura Abstract A new parallel algorithm has been developed for second-order Møller,Plesset perturbation theory (MP2) energy calculations. Its main projected applications are for large molecules, for instance, for the calculation of dispersion interaction. Tests on a moderate number of processors (2,16) show that the program has high CPU and parallel efficiency. Timings are presented for two relatively large molecules, taxol (C47H51NO14) and luciferin (C11H8N2O3S2), the former with the 6-31G* and 6-311G** basis sets (1032 and 1484 basis functions, 164 correlated orbitals), and the latter with the aug-cc-pVDZ and aug-cc-pVTZ basis sets (530 and 1198 basis functions, 46 correlated orbitals). An MP2 energy calculation on C130H10 (1970 basis functions, 265 correlated orbitals) completed in less than 2 h on 128 processors. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 407,413, 2006 [source] Origins and Applications of London Dispersion Forces and Hamaker Constants in CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2000Roger H. French The London dispersion forces, along with the Debye and Keesom forces, constitute the long-range van der Waals forces. London's and Hamaker's work on the point-to-point dispersion interaction and Lifshitz's development of the continuum theory of dispersion are the foundations of our understanding of dispersion forces. Dispersion forces are present for all materials and are intrinsically related to the optical properties and the underlying interband electronic structures of materials. The force law scaling constant of the dispersion force, known as the Hamaker constant, can be determined from spectral or parametric optical properties of materials, combined with knowledge of the configuration of the materials. With recent access to new experimental and ab initio tools for determination of optical properties of materials, dispersion force research has new opportunities for detailed studies. Opportunities include development of improved index approximations and parametric representations of the optical properties for estimation of Hamaker constants. Expanded databases of London dispersion spectra of materials will permit accurate estimation of both nonretarded and retarded dispersion forces in complex configurations. Development of solutions for generalized multilayer configurations of materials are needed for the treatment of more-complex problems, such as graded interfaces. Dispersion forces can play a critical role in materials applications. Typically, they are a component with other forces in a force balance, and it is this balance that dictates the resulting behavior. The ubiquitous nature of the London dispersion forces makes them a factor in a wide spectrum of problems; they have been in evidence since the pioneering work of Young and Laplace on wetting, contact angles, and surface energies. Additional applications include the interparticle forces that can be measured by direct techniques, such as atomic force microscopy. London dispersion forces are important in both adhesion and in sintering, where the detailed shape at the crack tip and at the sintering neck can be controlled by the dispersion forces. Dispersion forces have an important role in the properties of numerous ceramics that contain intergranular films, and here the opportunity exists for the development of an integrated understanding of intergranular films that encompasses dispersion forces, segregation, multilayer adsorption, and structure. The intrinsic length scale at which there is a transition from the continuum perspective (dispersion forces) to the atomistic perspective (encompassing interatomic bonds) is critical in many materials problems, and the relationship of dispersion forces and intergranular films may represent an important opportunity to probe this topic. The London dispersion force is retarded at large separations, where the transit time of the electromagnetic interaction must be considered explicitly. Novel phenomena, such as equilibrium surficial films and bimodal wetting/dewetting, can result in materials systems when the characteristic wavelengths of the interatomic bonds and the physical interlayer thicknesses lead to a change in the sign of the dispersion force. Use of these novel phenomena in future materials applications provides interesting opportunities in materials design. [source] Dispersion-Oriented Soft Interaction in a Frustrated Lewis Pair and the Entropic Encouragement Effect in its FormationCHEMISTRY - A EUROPEAN JOURNAL, Issue 48 2009Woo Kim Abstract The origin of the stability of a frustrated Lewis pair (FLP) tBu3P:B(C6F5)3 is investigated computationally to demonstrate the importance of the dispersion interaction. To this end, the interaction between alkyl-substituted phosphines (Me3P and tBu3P) and hexafluorobenzene (C6F6) is first investigated. Driven by the lone-pair to ,-orbital interaction, the binding energy is found to be even larger than usual ,,, interaction energies between small aromatic compounds. This character, which is inherited to fluorophenyl-substituted B(C6F5)3 in the FLP, induces large flexibility in the FLP over the molecular surface of B(C6F5)3. This soft interaction, in turn, causes an entropic stabilization of the FLP formation in comparison with classical Lewis pairs based on close and tight PB dative bonds. It also suggests a diverse nature of the FLP when it is involved in chemical reactions. Even with the cooperative participation of the perfluorophenyl groups, a detailed inspection of the FLP interaction potential energy surface indicates that the boron atom is still the major interaction site for the pair formation. This non-negligible direct PB interaction, which is related also to the soft nature of the borane frontier orbital, is further supported by substantial spatial overlap between the frontier orbitals on the phosphine/borane fragments and their interaction energy estimations. [source] Etched succinate-functionalized silica hydride stationary phase for open-tubular CECELECTROPHORESIS, Issue 22 2009Jian-Lian Chen Abstract An open-tubular (OT) CEC column was designed to anchor ionizable succinate-functionalized ligands onto a silica hydride-based stationary phase through surface etching, silanization, and hydrosilation reactions beginning from a bare fused-silica tube. The modified columns that were produced in each step were monitored by analysis of the effect of performance of EOF on the changes of pH values, concentrations, and the amount of ACN added in the running buffers. By tracking the EOF patterns between columns, the author determined that the surface composition of the final product column was a combination of silanols, silica hydrides, and succinate ligands. Furthermore, lower loading volumes of the succinate ligands prepared for the hydrosilation reaction served to complete the mixed-mode OT-CEC columns, and subsequently to carry out the separation of six phenyl alcohols. Studies on the elution order of these alcohols identified the presence of chromatographic interactions in addition to electrophoresis. Based on the employment of a solvation parameter model, these interactions likely included dispersion interactions, dipole-type interactions, and interactions arising through the polarizable electrons in the solute. The optimum buffer conditions for CEC separations of phenyl alcohols, carbonyl-substituted phenols, and a mixture of nucleosides and thymine were a phosphate buffer (50,mM, pH 10.51), a borate buffer (50,mM, pH 8.62), and a borate buffer (50,mM, pH 9.50), respectively. Overall, the hydride-based stationary phases with ionizable ligands were successfully applied to the OT-CEC separations, and these results confidently propose an ideal route to the synthesis of novel OT-CEC columns. [source] Evaluation of the intramolecular basis set superposition error in the calculations of larger molecules: [n]helicenes and Phe-Gly-Phe tripeptideJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2008Haydée Valdés Abstract Correlated ab initio calculations on large systems, such as the popular MP2 (or RI-MP2) method, suffer from the intramolecular basis set superposition error (BSSE). This error is typically manifested in molecules with folded structures, characterized by intramolecular dispersion interactions. It can dramatically affect the energy differences between various conformers as well as intramolecular stabilities, and it can even impair the accuracy of the predictions of the equilibrium molecular structures. In this study, we will present two extreme cases of intramolecular BSSE, the internal stability of [n]helicene molecules and the relative energies of various conformers of phenylalanyl-glycyl-phenylalanine tripeptide (Phe-Gly-Phe), and compare the calculated data with benchmark values (experimental or high-level theoretical data). As a practical and cheap solution to the accurate treatment of the systems with large anticipated value of intramolecular BSSE, the recently developed density functional method augmented with an empirical dispersion term (DFT-D) is proposed and shown to provide very good results in both of the above described representative cases. © 2007 Wiley Periodicals, Inc. J Comput Chem 2008 [source] Dispersion interactions in density-functional theoryJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2009Erin R. Johnson Abstract Density-functional theory (DFT) allows for the calculation of many chemical properties with relative ease, thus making it extremely useful for the physical organic chemistry community to understand and focus on various experiments. However, density-functional techniques have their limitations, including the ability to satisfactorily describe dispersion interactions. Given the ubiquitous nature of dispersion in chemical and biological systems, this is not a trivial matter. Recent advances in the development of DFT methods can treat dispersion. These include dispersion-corrected DFT (using explicit, attractive dispersion terms), parameterized functionals, and dispersion-correcting potentials, all of which can dramatically improve performance for dispersion-bound species. In this perspective, we highlight the achievements made in modeling dispersion using DFT. We hope that this will provide valuable insight to both computational chemists and experimentalists, who aim to study physical processes driven by dispersion interactions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Modulation of Stacking Interactions by Transition-Metal Coordination: Ab Initio Benchmark StudiesCHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2010Shaun Abstract A series of ab initio calculations are used to determine the CH,,,, and ,,,,,-stacking interactions of aromatic rings coordinated to transition-metal centres. Two model complexes have been employed, namely, ferrocene and chromium benzene tricarbonyl. Benchmark data obtained from extrapolation of MP2 energies to the basis set limit, coupled with CCSD(T) correction, indicate that coordinated aromatic rings are slightly weaker hydrogen-bond acceptors but are significantly stronger hydrogen-bond donors than uncomplexed rings. It is found that ,,,,, stacking to a second benzene is stronger than in the free benzene dimer, especially in the chromium case. This is assigned, by use of energy partitioning in the local correlation method, to dispersion interactions between metal d and benzene , orbitals. The benchmark data is also used to test the performance of more efficient theoretical methods, indicating that spin-component scaling of MP2 energies performs well in all cases, whereas various density functionals describe some complexes well, but others with errors of more than 1,kcal,mol,1. [source] | ||||||||||