Wave Function Modifications Research Articles

Factorial design and principal component analyses of the vibrational frequencies and infrared intensities of methane and silane

A multivariate statistical approach is presented to analyze the changes in calculated harmonic vibrational frequencies and infrared intensities obtained from ab initio calculations for methane and silane. The effects of four wave function modifications on these spectral parameters are investigated using a two-level factorial design and principal component analyses: basis set (6-31G and 6-311G), inclusion of polarization and diffuse functions as well as electron correlation treatment using the second-order Møller-Plesset method. Characteristic group frequencies present similar factorial models for each molecule. However, the intensity factorial models are quite different for these group vibrations. The most important effect values for the methane frequencies are due to a change from the Hartree-Fock to the second-order Møller-Plesset level. However, this effect is secondary to the one provoked by the inclusion of polarization functions in the silane basis set.

Multivariate statistical investigation of the effects of wave function modifications on the calculated vibrational frequencies and infrared intensities of CH 2F 2

Factorial design calculations for the vibrational frequencies and infrared intensities of CH 2F 2 are reported. Vibrational frequencies decrease by about 100 cm −1 compared with results obtained from Hartree-Fock wave functions when the second-order Møller-Plesset perturbation is applied. The inclusion of polarization functions increases the stretching frequencies by about 100 cm −1 and the CH 2 and CF 2 angular vibrations by about 50 cm −1, whereas it lowers the values of the CH stretching frequencies. CH 2F 2 calculated frequencies, which are found to have similar factorial design effects, also have optimal calculated results for the same wave function. Principal component projections of theoretical frequency and intensity results are shown to provide accurate graphical representations of how well these results agree with the experimental values. The factorial design models and principal component graphs of CH 2F 2 are found to be very similar to those of CH 3F for the calculated frequencies. However, these results are quite different for the calculated infrared intensities.

π plasmon in single (multi) shell nanotubes: a simple derivation of the shell interaction

Single (multi) shell nanotubes have been modelled with a cylindrical symmetry wall for the π electrons. This procedure leads to an easy derivation of the shell interaction effect on the π electron wavefunction in the multi shell nanotube case. The effect on the π plasmon frequency calculated in the random phase approximation due to the wavefunction modification has been investigated.

Enhancement of quantum confined Stark effect in a graded gap quantum well

A graded gap quantum well structure, where the band gap is linearly changing along the growth direction, is proposed for the enhancement of quantum confined Stark effect. Theoretical calculations show that the ground-state exciton peak energy shifts by a larger amount than in a usual square-shaped quantum well under an applied electric field. The wave function modifications in this quantum well result in a smaller decrease of the exciton oscillator strength, according to the electric field applied. These effects reveal the possibility of achieving high-performance optical modulators or other devices which utilize the quantum confined Stark effect.

Multiple Scattering Effects in a Three-particle System

We show that the phenomenological target wavefunction cutoff prescription arises naturally in the fixed scatterer approximation to particle scattering from a two-particle bound state. The wavefunction modification is found to describe the effects of higher order multiple scattering.

The influence of the accumulation layer on the conductance characteristics of MIS tunnel junctions

The inflex structure found by Tsui in conductance characteristics of InAsInAs oxidePb tunnel junctions at the bias equal to the bulk Fermi degeneracy is explained as a consequence of the modification of the semiconductor band wave functions by the accumulation layer.

Electronic levels in surface structures produced in oxygenation

Measurements are reported of energy distributions of Auger electrons ejected by He + ions from clean and oxygenated surfaces of Ni(111), GaSb(111)A and GaAs(111)A. The characteristic loss of higher energy electrons upon oxygenation is discussed in terms of a possible change in band structure in the surface layer of the crystal. The modification of wave functions caused by such a change could have the observed effect on the Auger distribution provided the surface energy band lies at lower energies relative to the vacuum level than does the bulk band.

Piezoresistance and Magnetoresistance in Impurity Conduction of Germanium

The effect of uniaxial compression along [111] on impurity conduction has been investigated in n-type germanium with intermediate concentration and with different compensation ratios. Activation energy of resistivity for compensated samples of antimony-doped germanium does not change with stress and is determined by the spacial configuration of impurities and by the extent of wave function derived from one valley. Magnetoresistance has been measured as a function of stress. Temperature dependence and anisotropy of positive magnetoresistance can be interpreted as modification of wave functions by a magnetic field. Negative magnetoresistance has been observed in most samples used and shows large anisotropy under stress. In the case of p-type germanium, which shows no negative magnetoresistance without stress, negative magnetoresistance is also observed under [100] compression.