# Two is company, three is a crowd - truncated many-body approaches for the treatment of molecular clusters

by Ricardo Mata (GFMUL, Portugal)

The quantum chemical treatment of molecular liquids is a challenging task, even by today's computer standards. In order to effectively observe bulk-like properties, a large number of molecules must be included in the calculation. However, conventional quantum chemical methods have a computational cost which scales at least with the fourth power of the system size. This limits the range of research to small clusters and/or low levels of accuracy.

In recent years, many-body approaches have been proposed, in which the
energy of the system is decomposed into 1-,2-,..., *N*-body terms. Due to the
weak interactions between the monomers, the series is known to converge
rather quickly, with the 3rd and 4th order expansions already showing close
to converged results. The topic of this talk is the attempt at further
truncating the *N*-body expansion while retaining the level of accuracy, and
designing a general linear scaling algorithm for use in the study of
molecular clusters.