The structure of naphthalene

The structure of naphthalene has been determined by ab initio gradient computation at the Hartree—Fock level using the 4–21 basis set. Special attention is paid to the small differences between the nearly equal C-C distances and to evaluation of the ability of electron diffraction experiments to distinguish among them. The computed orbital energies are used to assign the photoelectron spectrum.     

Vibrational analyses employing cartesian coordinates

Geometry-optimised ab initio (STO-3G minimal basis set) calculations have been carried out for S-trans and orthogonal forms of 1,3-butadiene. The central C-C bond is shorter (1.482 Å) in the S-trans form than the orthogonal form (1.504 Å). Calculations on the orthogonal form indicate that the additional bond length decrease destabilizes the σ bond. the stabilization of the S-trans form being associated with conjugative (or π delocalization) effects.     

Ab initio studies of structural features not easily amenable to experiment: Part 15. The influence of solvation on molecular structure in some formic acid and carbonic acid hydrates

The completely relaxed ab initio geometries (4—21G) of a trihydrate of carbonic acid and of the monohydrates of cis and trans formic acid are compared with the corresponding unhydrated structures. The maximum structural changes caused by hydration in the free acid structures are of the order of magnitude of 0.03 Å and 3° for bond distances and bond angles, respectively. The corresponding changes in free and complexed water are 0.005 Å and 5°, respectively. The results are significant for the general problem of the transferability of gas phase molecular structures to molecules in solution and for estimates of the uncertainties in theoretical hydration energy surfaces which are generated by using fixed, monomer geometries for water and solvate molecules. Compared with the free geometries, the sum total of the structural changes in some of the systems studied corresponds to energies of several kcal mol^?1.     

On the interaction of palladium with olefinic systems

We have performed all electron Hartree–Fock gradient calculations and geometry optimizations on systems composed of one to three palladium atoms and: CH₃ cation and anion, C₂H₄, C₂H₃NH₂, C₄H₄, NH₃, and (NH₃) + (C₂H₄). Several basis set considerations are discussed and the binding energies of Pd to these small molecules are reported. We find the counterpoise correction to the binding energies of these systems to be large. We also present MP2 calculations of the palladium binding energy with a large uncontracted palladium spd basis set in the PdC₂H₄ and PdNH₃ systems. The binding interaction between ethylene and palladium results in a mixing of the 4d–π* and 5s–π orbitals, and, is dissociative to the ethylene. The palladium-butadiene and palladium-cyclobutene relative stabilites and structures are interesting since these molecules could form from acetylene on a palladium surface. We find the Pd-butadiene cyclic structure to be 43 kcal/mol more stable than the Pd-cyclobutene product.     

Scanning photoluminescent spectroscopy of bioconjugated quantum dots

We report on the application of the bio-conjugated quantum dots (QDs) for a “sandwich” enzyme-linked immunosorbent assay (ELISA) cancer testing technique. Quantum dot ELISA detection of the cancer PSA antigen at concentrations as low as 0.01 ng/ml which is ～50 times lower than the classic “sandwich” ELISA was demonstrated. Scanning photoluminescence (PL) spectroscopy was performed on dried ELISA wells and the results compared with the same QD samples dried on a solid substrate. We confirmed a “blue” up to 37 nm PL spectral shift in a case of QDs conjugated to PSA antibodies. Increasing of the “blue” spectral shift was observed at lower PSA antigen concentrations. The results can be used to improve sensitivity of “sandwich” ELISA cancer antigen detection.     

The C2-DIIS convergence acceleration algorithm

We present a theoretical and numerical comparison between two DIIS algorithms to which we refer herein as C ¹-DIIS and C ²-DIIS . The C ²-DIIS algorithm is shown to be equivalent to the traditional C ¹-DIIS algorithm near convergence and more stable numerically as regards the accumulation of round-off error when the C ¹-DIIS equations become (nearly) singular. The C ²-DIIS algorithm also offers alternative solutions to the DIIS equations when anharmonicities or numerical difficulties are problematic. These properties of the C ²-DIIS algorithm allow the use of much larger DIIS spaces, obviating the need for truncation of the DIIS space, which, when done, usually results in a loss of information contained in the iterated subspace. The C ²-DIIS method can be considered to be a variant of the singular value decomposition method. © 1993 John Wiley & Sons, Inc.     

Ab initio studies of structural features not easily amenable to experiment: The molecular structures of two low-energy forms of unionized serine

The structures of two unionized conformations of serine were refined without geometrical constraints using standard single determinant ab initio procedures on the 4-21G level. The results represent the best now available estimate for the unobserved equilibrium geometry of this system.