Results and discussion In this section, we present the results of three model studies in which we test the reliability of the embedded cluster model developed for the brucite (0001) surface. First, we examine the adsorption of charged systems, by investigating the interaction of a series of s block ions with brucite. Then, we move on to compare the embedded model calculations with a more widely established method (periodic DFT); we perform a substitution study for single ions into brucite and a second in which we look at the adsorption of differently coordinated [Sr(OH)2(H2O)4] complexes on the surface, comparing their relative stability. We also used the periodic DFT model to carry out cell size studies on the systems of interest and to (indirectly) verify the size of the quantum chemically treated cluster in the PEECM approach. Note that the adsorption and substitution energies presented in sections 3.1 and 3.2 are calculated without considering the effects of solvation on the adsorbed or substituted ions. This has been done because the purpose of these calculations is to provide as direct and straightforward a comparison of periodic DFT and PEECM as possible, without the extra variability and complication that will inevitably arise from the treatment of solvation. Single ion adsorption of Sr2+ and other s block elements on brucite We calculated adsorption energies for a series of ions: Na+, Rb+, Cs+ and Mg2+, Sr2+, Ba2+ from which Na+, Cs+, Sr2+ and Mg2+ are known to exist in the aqueous phase in Magnox storage ponds.35 As described in the Introduction, we have a special interest in 90Sr2+ and 137Cs+, as their adsorption behaviour is especially important in the waste treatment process. We included Rb+ and Ba2+ to make the series of the singly and doubly charged ions more complete, and to allow us to test if the adsorption energies follow the trend expected based on the ionic radii and charges, the i.e. dications should have a stronger interaction with the surface, and the interaction energy should decrease with decreasing ionic charge density. The following equation was used to calculate the adsorption energies presented in Table I:
Results and discussion In this section, we present the results of three model studies in which we test the reliability of the embedded cluster model developed for the brucite (0001) surface. First, we examine the adsorption of charged systems, by investigating the interaction of a series of s block ions with brucite. Then, we move on to compare the embedded model calculations with a more widely established method (periodic DFT); we perform a substitution study for single ions into brucite and a second in which we look at the adsorption of differently coordinated [Sr(OH)2(H2O)4] complexes on the surface, comparing their relative stability. We also used the periodic DFT model to carry out cell size studies on the systems of interest and to (indirectly) verify the size of the quantum chemically treated cluster in the PEECM approach. Note that the adsorption and substitution energies presented in sections 3.1 and 3.2 are calculated without considering the effects of solvation on the adsorbed or substituted ions. This has been done because the purpose of these calculations is to provide as direct and straightforward a comparison of periodic DFT and PEECM as possible, without the extra variability and complication that will inevitably arise from the treatment of solvation. Single ion adsorption of Sr2+ and other s block elements on brucite We calculated adsorption energies for a series of ions: Na+, Rb+, Cs+ and Mg2+, Sr2+, Ba2+ from which Na+, Cs+, Sr2+ and Mg2+ are known to exist in the aqueous phase in Magnox storage ponds.35 As described in the Introduction, we have a special interest in 90Sr2+ and 137Cs+, as their adsorption behaviour is especially important in the waste treatment process. We included Rb+ and Ba2+ to make the series of the singly and doubly charged ions more complete, and to allow us to test if the adsorption energies follow the trend expected based on the ionic radii and charges, i.e. the dications should have a stronger interaction with the surface, and the interaction energy should decrease with decreasing ionic charge density. The following equation was used to calculate the adsorption energies presented in Table I:
PEECM_paper_postref_clean.docx