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Momentum Profiles for Open-Shell Molecules: Studies of the HOMO's of NO, O<sub>2</sub>, and NO<sub>2</sub> by Electron Momentum Spectroscopy and SCF, Post-Hartree-Fock and DFT Calculations

TitleMomentum Profiles for Open-Shell Molecules: Studies of the HOMO's of NO, O2, and NO2 by Electron Momentum Spectroscopy and SCF, Post-Hartree-Fock and DFT Calculations
Publication TypeJournal Article
Year of Publication1995
AuthorsRolke, J, Cann, N, Zheng, Y, Hollebone, BP, Brion*, CE, Wang, YA, Davidson, ER
JournalChem. Phys.
Volume201
Pagination1-21
Date PublishedDec
Type of ArticleArticle
ISBN Number0301-0104
KeywordsCORRELATED WAVEFUNCTIONS, CORRELATION ENERGIES, density, DIPOLE-MOMENT, EXCHANGE-ENERGY, GAUSSIAN-BASIS SETS, NITRIC-OXIDE, VALENCE ORBITALS, VARIATIONAL PERTURBATION-THEORY, WAVE-FUNCTIONS
Abstract

Measurements of the outermost valence electron orbital momentum profiles of the open shell molecules NO, O-2 and NO2 have been obtained using electron momentum spectroscopy (EMS). The presently reported experimental momentum profiles of NO and O-2 display much improved statistics compared with previously published EMS results while the data for the HOMO of NO, is the first reported. In the case of NO, the present measurements are considerably different from previous results and these differences appear to be due to the presence of NO2 impurities in the previous work. The EMS measurements provide a stringent test of basis set effects and the quality of ab initio methods in the description of these open shell systems. The experimental momentum profiles have been compared with theoretical spherically averaged momentum profiles from several basis sets calculated at the level of the target Hartree-Fock approximation (THFA) with a range of basis sets using both unrestricted Hartree-Fock (UHF) and restricted open shell Hartree-Fock (ROHF) methods. Various configuration interaction calculations such as multi-reference singles and doubles configuration interaction (MRSD-CI), averaged coupled pair functional (ACPF) and quasi-degenerate variational perturbation theory (QDVPT) calculations of the full ion-neutral overlap amplitude have also been compared to experiment to investigate the effects of electron correlation and relaxation. The experimental momentum profiles have further been compared to calculations at the level of the target Kohn-Sham approximation (TKSA) using density functional theory (DFT) with the local density approximation and also with gradient corrected exchange-correlation potentials. In addition to momentum profiles, other electronic properties such as total energies, dipole moments, quadrupole moments and values of the electronic spatial extent have been calculated by the various theoretical methods and compared to experimental values.

URL<Go to ISI>://A1995TH20500001