Contract B590089: Technical Evaluation of the Pu Cluster Calculations

Abstract

Contract B590089: Technical Evaluation of the Pu Cluster CalculationsTobin, LLNL Page 18 November 2011 2Comparison 1: X--ray Photoelectron Spectroscopy (XPS), Bremstrahlung Isochromat Spectroscopy (BIS), also known as Inverse Photoelectron Spectroscopy (IPES), and X--ray Absorption Spectroscopy (XAS) versus cluster calculation results for UO2.The experimental results (bottom) are from References 1 and 2 and the theoretical results (top) are from Appendix C. This is very promising. Because we inserted a band--gap of 2.1 eV artificially, the density of states (DOS) calculations have been split at the energy zero and aligned with the valence band maximum (VBM) in the XPS and the Conduction Band Minimum (CBM) in the BIS and XAS. UDOS is the unoccupied density of states. ODOS is the occupied density of states. While others have already made such comparisons with XPS and the ODOS [Y.A. Teterin and A.Y. Teterin, Russian Chemical Reviews 73, 541 (2004)], this is the first such definitive comparison of the ODOS with the BIS and XAS. In general, there is strong agreement in terms of the U6d, U5f, and O2p DOS with the spectral features. Contract B590089: Technical Evaluation of the Pu Cluster CalculationsTobin, LLNL Page 18 November 2011 3Comparison 2: Synchrotron--Radiation--based Photoelectron Spectroscopy (PES) versus cluster calculation results for PuO2.The experimental results (top) are from Reference 3 and the theoretical results (bottom) are from Appendix C. This Pu spectrum are from an alpha--Pu sample with a delta--Pu surface reconstruction. By working at the Cooper Minimum, the relative intensity of the Pu 5f can be diminished and the contribution of the other peaks amplified. Clearly, there is once again strong agreement between the ODOS for the Pu5f, O2p, Pu6p3/2, O2s, and Pu6p1/2 and the corresponding spectroscopic features. Contract B590089: Technical Evaluation of the Pu Cluster CalculationsTobin, LLNL Page 18 November 2011 4Comparison 3: Synchrotron--Radiation--based Photoelectron Spectroscopy (PES) versus cluster calculation results for Pu.The experimental results (bottom) are from Reference 3 and the theoretical results (top) are from Appendix B. These Pu spectra are from an alpha--Pu sample with a delta--Pu surface reconstruction. The calculations once again provide a meaningful simulation of the observed states: Pu5f, Pu6d, Pu6p3/2 and Pu6p1/2. By tuning the photon energy, different states can be emphasized and de--emphasized. At the anti--resonance, hv = 100 eV, the Fermi Edge step should be representative of the Pu 6d states. On Resonance, hv = 125 eV, the Fermi Edge should be dominated by the Pu5f states. Despite the small amount of oxidation, these spectra should provide accurate basis for comparison with bulk, metallic Pu. Contract B590089: Technical Evaluation of the Pu Cluster CalculationsTobin, LLNL Page 18 November 2011 5Comparison 4: 5f occupations. One of the crucial issues in Pu electronic structure is that of the differentiation of the 6d and 5f states. Where are the Pu5f and Pu 6d states?...