Quantum chemical calculations of Xray emission spectroscopyTools Wadey, J.D. and Besley, Nicholas A. (2014) Quantum chemical calculations of Xray emission spectroscopy. Journal of Chemical Theory and Computation, 10 (10). pp. 45574564. ISSN 15499618
Official URL: http://pubs.acs.org/doi/abs/10.1021/ct500566k
AbstractThe calculation of Xray emission spectroscopy with equation of motion coupled cluster theory (EOMCCSD), time dependent density functional theory (TDDFT) and resolution of the identity single excitation configuration interaction with second order perturbation theory (RICIS(D)) is studied. These methods can be applied to calculate Xray emission transitions by using a reference determinant with a corehole, and they provide a convenient approach to compute the Xray emission spectroscopy of large systems since all of the required states can be obtained within a single calculation removing the need to perform a separate calculation for each state. For all of the methods, basis sets with the inclusion of additional basis functions to describe core orbitals are necessary, particularly when studying transitions involving the 1s or bitals of heavier nuclei. EOMCCSD predicts accurate transition energies when compared with experiment, however, its application to larger systems is restricted by its computational cost and difficulty in converging the CCSD equations for a corehole reference determinant, which become increasing problematic as the size of the system studied increases. While RICIS(D) gives accurate transition energies for small molecules containing first row nuclei, its application to larger systems is limited by the CIS states providing a poor zeroth order reference for perturbation theory which leads to very large errors in the computed transition energies for some states. TDDFT with standard exchangecorrelation functionals predicts transition energies that are much larger than experiment. Optimization of a hybrid and shortrange cor rected functional to predict the Xray emission transitions results in much closer agreement with EOMCCSD. The most accurate exchangecorrelation functional identified is a modified B3LYP hybrid functional with 66% HartreeFock exchange, denoted B66LYP, which predicts Xray emission spectra for a range of molecules including fluorobenzene, nitrobenzene, ace tone, dimethyl sulfoxide and CF3Cl in good agreement with experiment.
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