Electronic structure calculations, changes

When a tunneling calculation is undertaken, many simplifications render the task easier than a complete transport calculation such as the one of [32]. Let us take the formulation by Caroli et al. [16] using the change induced by the vibration in the spectral function of the lead. In this description, the current and thus the conductance are proportional to the density of states (spectral function) of the leads (here tip and substrate). This is tantamount to using some perturbational scheme on the electron transmission amplitude between tip and substrate. This is what Bardeen s transfer Hamiltonian achieves. The main advantage of this approximation is that one can use the electronic structure calculated by some standard way, for example plane-wave codes, and use perturbation theory to account for the inelastic effect. In [33], a careful description of the Bardeen approximation in the context of inelastic tunneling is given, and how the equivalent of Tersoff and Hamann theory [34,35] of the STM is obtained in the inelastic case. 

Equations (5) and (8) give information on the mode symmetry without performing a complex electronic structure calculation. Equation (5) gives us the spatial distribution of the change in conductance. It basically tells us that the tip will plot the state Vv(ro) °f Eq. (6). We see that the matrix... 

The sudden changes in the adiabatic wavefunctions near avoided crossings make it more convenient to use diabatic potential energy surfaces when simulating photodissociation dynamics. The adiabatic potentials, usually constructed from electronic structure calculation data, should therefore be transformed to diabatic potentials. The adiabatic-diabatic transformation yields diabatic states for which the derivative couplings above approximately vanish. The diabatic potential energy surfaces are obtained from the adiabatic ones by a unitary orthogonal transformation [22,23]... 

The goal of electronic-structure calculations is to provide information on real materials. The field of electronic-structure calculations is therefore placed somewhere between experiment and theory. I.e., by carrying through such calculations on specific systems one obtains results that cannot be manipulated but instead have to be interpreted. This resembles the situation of experiment. On the other hand, by modifying the systems one is able to follow the changes in the properties also to idealized situations that lie outside the range of experiment, which is a typical approach within theory. 

Y.T. Lee (lAMS) for providing the experimental setup for these experiments, and O. Asvany and L.C.L. Huang for experimental assistance. Special thanks to Y. Osamura, P.v.R. Schleyer, H.F. Schaefer, H.F. Bettinger, and F. Stahl for performing electronic structure calculations on these reactions. We are also indebted to Prof. A.H.H. Chang (Department of Chemistry, National Dung Hua University, Hualien, ROC) for carrying out RRKM calculations. 

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