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

Abstract

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-ζ 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.

A high‐resolution electron momentum spectroscopy and density functional theory study into the complete valence electronic structure of allene

“…In our previous studies on 1,3‐butadiene,16 [1.1.1]propellane,17 and cubane,18 there were always experimental MDs, for one or two of the respective molecular orbitals, that could be used to make a clear distinction between the quality of the various basis sets and XC functionals that we employed in our DFT calculations 35. Here, however, the situation is not so transparent.…”

“…Experimental validation of Hartree–Fock or density functional basis sets using EMS may provide a route to appropriate basis sets for calculating other types of molecular properties,35 such as molecular geometries, NMR, vibrational spectra, and charge distributions etc. In this work we have taken our “optimum” DFT‐BP/TZVP basis set and used it to derive some of these molecular properties.…”

High resolution infrared spectroscopy of [1.1.1]propellane

“…In the context of the times that these studies were undertaken, they constituted an important source of information that, coupled with quantum theoretical calculations, gave information about the quadratic force fields, normal coordinates, and dipole moment derivatives for these molecules, and allowed some conclusions to be drawn regarding the similarities and dissimilarities of their chemical bonding not only with respect to one another, but also with respect to cyclopropane, which may be considered to be their predecessor molecule. Other work dealt with the photoelectron spectroscopy of propellane [29][30][31][32][33][34][35][36], ab initio calculations of its NMR spectra [37][38][39], and a new theoretical study of its vibrational spectrum and structure [40]. The present account deals primarily with the determination of the ground state constants of propellane, gained from analyzing nine fundamental and four combination infrared bands.…”

Wavefunctions derived from experiment. I. Motivation and theory

“…They suggest that a wavefunction comprised of these orbitals, since it is derived from experiment, should lead to`more accurate molecular-property information'. In fact, Adcock et al (1998) have performed DFT calculations on these molecules using a variety of basis sets, and have shown that those basis sets which best reproduced the (e, 2e) data were also those which yielded the best molecular geometrical parameters compared to experiment.…”