An examination of the Brueckner condition for the selection of molecular orbitals in correlated wavefunctions

The Brueckner condition is analyzed as an approximation to the condition of stability of the total energy with respect to variations in the orbitals. The recently introduced method of self-consistent electron pairs is used to find Brueckner orbitals and it is shown that the Brueckner condition can give a slightly higher energy wavefunction than with Hartree—Fock orbitals, while a slightly lower energy result is obtained when singly substituted configurations are important.     

An ab initio study of the stability and electronic structure of univalent magnesium salts

Large basis and well-correlated ab initio electronic structure calculations have been performed on the simple Mg(I) salts, Mg₂F₂ and Mg₂Cl₂. The electron withdrawing power of the halogens gives rise to significant metal-metal bonding and consequently these as yet unobserved, univalent salts are calculated to be 10–12 kcal more stable than if the second magnesium atom were absent from the molecule. With this stability, these species provide an energetically more accessible Mg atom for subsequent reaction than does solid magnesium where the atomization energy is 35 kcal. Thus, formal univalency of magnesium affords a route to activated magnesium.     

General quantum mechanical operators. An open-ended approach for one-electron integrals with Gaussian bases

A universal computational approach for evaluating integrals over gaussian basis functions for general operators of the form is presented. The implementation is open-ended with respect to the types of basis functions (s, p, d, f, g, h…) and with respect to the integers that specify the operator. These one-electron integrals comprise operators associated with electrical and magnetic properties of molecules and include those needed to find multipole polarizabilities, multipole susceptibilities, chemical shifts, and so on. The scheme also generates the usual kinetic, nuclear attraction, and overlap operators.     

Diacetylene's weak bonding to acetylene clusters

An interaction potential previously developed for the acetylene–polyyne dimer was used to explore the interaction potential surfaces for clusters containing a diacetylene molecule and two or more acetylene molecules. Ab initio calculations were performed on the smallest clusters in order to assess the energetic and structural features predicted by the model potential. The preferred arrangements of the monomers in the clusters maximize the favorable quadrupole–quadrupole interactions between the monomers.     

Complementary peptide sequence coverage using alternative enzymes for on-line digestion with a triaxial electrospray probe

Using alternative enzymes for on-line digestion with a triaxial electrospray probe extends sequence coverage. This is the first report of utilization of our triaxial probe for on-line analysis with enzymes other than pepsin, suggesting potential for broader application. The probe allows access to processes occurring on a timescale and/or involving substrate conformations complementary to those for conventional (off-line) digestion. Some of the features observed in application to Aβ fibrils are suggestive of unique reactive intermediates during dissolution. Data obtained with enzyme mixtures suggest synergistic effects.     

A Fenchel Duality Aspect of Iterative I-Projection Procedures

In this paper we interpret Dykstra's iterative procedure for finding anI-projection onto the intersection of closed, convex sets in terms of itsFenchel dual. Seen in terms of its dual formulation, Dykstra's algorithm isintuitive and can be shown to converge monotonically to the correctsolution. Moreover, we show that it is possible to sharply bound thelocation of the constrained optimal solution.     

A mobile one-sided NMR sensor with a homogeneous magnetic field: the NMR-MOLE

A new portable NMR sensor with a novel one-sided access magnet design, termed NMR-MOLE (MObile Lateral Explorer), has been characterised in terms of sensitivity and depth penetration. The magnet has been designed to be portable and create a volume with a relatively homogeneous magnetic field, 15,000 ppm over a region from 4 to 16 mm away from the probe, with maximum sensitivity at a depth of 10 mm. The proton NMR frequency is 3.3 MHz. We have demonstrated that with this approach a highly sensitive, portable, unilateral NMR sensor can be built. Such a design is especially suited for the characterisation of liquids in situations where unilateral or portable access is required.