The divide-expand-consolidate (DEC) scheme provides a means of overcoming the scaling wall associated with canonical coupled cluster (CC) electronic structure calculations on large molecular systems. Taking advantage of the local nature of correlation effects, the correlation energy for the full molecule is calculated from a set of independent fragments using localized molecular orbitals. In contrast to standard CC calculations, the resulting DEC scheme is highly parallelizable and linear-scaling. Another benefit of the DEC scheme which has not yet been exploited is that the independent nature of the fragment calculations allows for the evaluation of the correlation energies of the fragments at different levels of theory. In this study, we report the implementation of a Multilayer DEC (ML-DEC) scheme in which higher level theory can be performed on areas of interest within a large system. For example, adsorption sites, defects or active sites maybe be treated at a high level of theory, while the remaining fragments are modeled at a lower level in order to reduce computational cost. The ML-DEC scheme is utilized in the calculation of adsorption energies for a number of small molecules, including acid gases, on the open metal sites of a finite Mg-MOF-74 model system. The results of these calculations are used to draw conclusions about the relative adsorption strengths of small molecules in pristine and defective Mg-MOF-74.

Multilayer divide-expand-consolidate methods applied to the study of gas adsorption in Mg-based metal-organic frameworks (MOF-74)

255th National Meeting (2018)

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