Volume 117, Issue 21, 01 December 2002
Index of content:
117(2002); http://dx.doi.org/10.1063/1.1524155View Description Hide Description
The excitation of a fullerene-cage vibrational mode by inelastic tunnelingelectrons has been observed on single molecules adsorbed on Ag(110). The vibration is assigned to the mode. A critical enhancement of the inelastic signal was found on fullerenes oriented along one of their symmetry axis upon adsorption. In strong coincidence, those fullerenes maintain a resonance structure at the Fermi level that resembles the first unoccupied molecular orbital distribution of a free molecule, as determined by comparison with ab initio calculations. The degree of symmetry of the adsorbed fullerene is found to be crucial for resonant mechanism of vibrational excitation. We also propose that mode degeneracy splitting may reduce mode detection.
117(2002); http://dx.doi.org/10.1063/1.1523393View Description Hide Description
Traditional methods for characterizing an optimized molecular structure as a minimum or as a saddle point on the nuclear potential energy surface require the full Hessian. However, if denotes the number of nuclear degrees of freedom, a full Hessian calculation is more expensive than a single point geometry optimization step by the order of magnitude of Here we present a method which allows to determine the lowest vibrational frequencies of a molecule at significantly lower cost. Our approach takes advantage of the fact that only a few perturbed first-order wave functions need to be computed in an iterative diagonalization scheme instead of ones in a full Hessian calculation. We outline an implementation for Hartree–Fock and density functional methods. Applications indicate a scaling similar to that of a single point energy or gradient calculation, but with a larger prefactor. Depending on the number of soft vibrational modes, the iterative method becomes effective for systems with more than 30–50 atoms.
117(2002); http://dx.doi.org/10.1063/1.1524181View Description Hide Description
The initial state selected time-dependent wave packet method has been developed to study the reaction in seven dimensions by employing the model developed by Palma and Clary [J. Chem. Phys. 112, 1859 (2000)]. The latter eight-dimensional model only assumes that the nonreacting group keeps a symmetry in reaction. The CH bond lengths in the nonreacting group were fixed in the study to reduce the number of degrees of freedom to seven. Our calculations reveal that it is very important to accurately deal with the umbrella motion of the group while studying this reaction. We investigated the effects of the fundamental vibrational excitations of on the reaction. Finally, we compare our rate constant for the ground rovibrational initial state with available experimental and other theoretical results.
117(2002); http://dx.doi.org/10.1063/1.1523899View Description Hide Description
Second-order Moller–Plesset perturbation theory investigations indicate that the highly strained three- and four-membered semiconductor ring systems and Cl, Br) exhibit aromaticities featured with the delocalized π orbitals perpendicular to the ring planes.
117(2002); http://dx.doi.org/10.1063/1.1524154View Description Hide Description
We have carried out first-principles density functional calculations for clusters of the coinage metals containing thirteen atoms where Ag, or Au). We find that for this geometric “magic number” the low energy isomers are actually disordered, forming almost a continuous distribution as a function of energy.