Insights into theoretical quantum chemistry from electron momentum spectroscopy

1996 ◽  
Vol 74 (11-12) ◽  
pp. 757-762 ◽  
Author(s):  
Ernest R. Davidson
Keyword(s):  
Hydrogen Bond ◽  
Wave Function ◽  
Binding Energy ◽  
Quantum Chemistry ◽  
Excited States ◽  
Momentum Density ◽  
Water Dimer ◽  
Basis Sets ◽  
Electron Momentum ◽  
Electron Momentum Spectroscopy

Most basis sets used in quantum chemistry are designed to get the correct charge and momentum density in the region important for covalent bonding. The (e,2e) cross section measured by electron momentum spectroscopy (EMS) emphasizes the low-momentum, large r, region of the wave function. Improving the description of this part of the wave function for water has resulted in good agreement with (e,2e) data. Because the hydrogen bond is sensitive to the long-range tail of the wave function, this has simultaneously led to an improved description of the hydrogen bond in the water dimer. The satellite region of the binding energy spectrum gives information about the excited states of the cation that is not available at present from any other form of spectroscopy. Calculations seeking agreement with the binding-energy spectra and the momentum distribution associated with satellite peaks have led to the most complete catalog of the cation excited states for ethylene. Here we report the assignment of the excited states based on the dominant part of the wave function rather than focusing on the small coefficients that describe the intensity borrowing from the primary holes. We also examine the adequacy of the assumption that every Dyson orbital is similar to one of the Hartree–Fock orbitals.

scholarly journals Application of DFT and EMS to the Study of Strained Organic Molecules

1998 ◽  
Vol 51 (4) ◽  
pp. 707 ◽  
Author(s):  
W. Adcock ◽  
M. J. Brunger ◽  
M. T. Michalewicz ◽  
D. A. Winkler
Keyword(s):  
Wave Function ◽  
Density Functional ◽  
Impulse Approximation ◽  
Basis Sets ◽  
Functional Theory ◽  
Electron Momentum ◽  
Plane Wave Impulse Approximation ◽  
Electron Momentum Spectroscopy ◽  
Momentum Distributions ◽  
Self Consistent Field

Electron momentum spectroscopy (EMS) studies of the valence shells of [1.1.1]propellane, 1,3-butadiene, ethylene oxide and cubane are reviewed. Binding energy spectra were measured in the energy regime of 3·5–46·5 eV over a range of different target electron momenta, so that momentum distributions (MDs) could be determined for each ion state. Each experimental electron momentum distribution is compared with those calculated in the plane wave impulse approximation (PWIA) using both a triple-? plus polarisation level self-consistent field (SCF) wave function and a further range of basis sets as calculated using density functional theory (DFT). A critical comparison between the experimental and theoretical momentum distributions allows us to determine the ‘optimum’ wave function for each molecule from the basis sets we studied. This ‘optimum’ wave function then allows us to investigate chemically or biologically significant molecular properties of these molecules. EMS-DFT also shows promise in elucidating the character of molecular orbitals and the hybridisation state of atoms.

Exact Numerical Procedure for the Binding Energy of Hydrogen Impurities in Quantum Dots with Parabolic Confinements

2013 ◽  
Vol 475-476 ◽  
pp. 1355-1358
Author(s):  
Arnold Abramov
Keyword(s):  
Quantum Dots ◽  
Wave Function ◽  
Binding Energy ◽  
Quantum Dot ◽  
Excited States ◽  
Ground State ◽  
Qualitative Agreement ◽  
Numerical Procedure ◽  
Impurity States ◽  
Parabolic Confinement

In this paper we present exact numerical procedure to calculate the binding energy and wave function of impurity states in a quantum dot with parabolic confinement. The developed method allows control the accuracy of obtained results, as well as calculates the characteristics of not only ground state, but also of the excited states. Comparison of our results with data obtained by other methods is in quantitative and qualitative agreement. We studied the effects of impurity position on the binding energy.

scholarly journals The Development of Electron Momentum Spectroscopy

1991 ◽  
Vol 44 (3) ◽  
pp. 277 ◽  
Author(s):  
Erich Weigold
Keyword(s):  
Electronic Structure ◽  
Excited States ◽  
Ground State ◽  
Correlation Effects ◽  
Optically Pumped ◽  
Electron Momentum ◽  
Excited Atoms ◽  
Electron Momentum Spectroscopy ◽  
Momentum Distributions ◽  
Polarised Light

The study of the valence electronic structure of atoms and molecules by (e,2e) spectroscopy, or EMS as it is now known, began in the early 1970s with a series of measurements at Flinders University. The first measurements were on argon, and they showed the importance of correlation effects in the inner valence 3s shell. The first molecular experiments were on methane, and they showed the sensitivity of the momentum distributions to details of the orbital wavefunctions. Until recently all EMS measurements were made on ground state targets with random orientations. We have, however, now made successful EMS measurements on excited states and oriented targets. Sodium atoms in the 32S1/2(F=2) ground state are optically pumped by right-handed circularly polarised light to the excited 32P3/2(F'=3, 1'111"=3) state. Thus the excited atoms are all in the I .e=l, me=l} state. These measurements are discussed in some detail.

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