A first principles study of the adsorption and dissociation of CO_2 on the δ-Pu (111) surface

摘要

A complete understanding of the nature of the 5f electrons has been and continues to be a major scientific problem in condensed matter physics. Bulk and surface electronic structure studies of the actinides as also atomic and molecular adsorptions on the actinide surfaces provide a path towards this understanding. In this work, ab initio calculations within the framework of density functional theory have been used to study the adsorption of molecular CO_2 and the corresponding partially dissociated (CO + O) and completely dissociated (C + O + O) products on the δ-Pu (111) surface. The completely dissociated C + O + O configurations exhibit the strongest binding with the surface (7.92 eV), followed by partially dissociated products CO +0(5.08 eV), with molecular CO_2 adsorption having the lowest binding energies (2.35 eV). For all initial vertically upright orientations, the CO_2 molecule physisorbs or do not bind to the surface and the geometry and orientation do not change. For all initial flat lying orientations chemisorption occurs, with the final state corresponding to a bent CO_2 molecule with bond angles of 117°- 130° and the elongation of the CO bond. For CO + O co-adsorption, the stable configurations corresponded to CO dipole moment orientations of 100°-172° with respect to the surface normal and the elongation of the CO bond. The most stable chemisorption cases correspond to anomalously large rumpling of the top Pu layer. The interactions of the CO_2 and CO with the Pu surface have been analyzed using the energy density of states and difference charge density distributions. The nature and the behavior of the 5f electrons have also been discussed in detail in the context of this study.