Volume 130, Issue 24, 28 June 2009
Index of content:
The presence of a chiral surface can alter the characteristics of nearby solvent molecules such that, on average, these molecules become chiral. The extent of this induced chirality and its dependence on the surface and solvent characteristics are explored in this article. Three surfaces employed in chiral chromatography are examined: The Whelk-O1 interface, a phenylglycine-derived chiral stationary phase (CSP), and a leucine-derived CSP. All three interfaces are “brush type” in that the chiral molecules are attached to the underlying substrate via an achiral tether. The solvents consist of ethanol, a binary -hexane/ethanol solvent, 2-propanol, and a binary -hexane/2-propanol solvent.Molecular dynamics simulations of the solvated chiral interfaces form the basis of the analysis. The chirality induced in the solvent is assessed based on a chirality index originally proposed by Osipov et al. [Mol. Phys.84, 1193 (1995)]. Solventchirality will depend on the solvent position relative to the surface. For this reason, a position-dependent chirality index is analyzed in detail.
Local explicitly correlated coupled-cluster methods: Efficient removal of the basis set incompleteness and domain errors130(2009); http://dx.doi.org/10.1063/1.3160675View Description Hide Description
We propose an explicitly correlated local LCCSD-F12 method in which the basis set incompleteness error as well as the error caused by truncating the virtual orbital space to pair-specific local domains are strongly reduced. This is made possible by including explicitly correlated terms that are orthogonalized only to the pair-specific configuration space. Thus, the contributions of excitations outside the domains are implicitly accounted for by the explicitly correlated terms. It is demonstrated for a set of 54 reactions that the reaction energies computed with the new LCCSD-F12 method and triple-zeta basis sets deviate by at most 2.5 kJ/mol from conventional CCSD complete basis set results (RMS: 0.6 kJ/mol). The local approximations should make it possible to achieve linear scaling of the computational cost with molecular size.