During the past decades, quantum mechanical methods have undergone an amazing transition from pioneering investigations of experts into a wide range of practical applications, made by a vast community of researchers. First principles calculations of systems containing up to a few hundred atoms have become a standard in many branches of science. The sizes of the systems which can be simulated have increased even further during recent years, and quantum-mechanical calculations of systems up to many thousands of atoms are nowadays possible. This opens up new appealing possibilities, in particular for interdisciplinary work, bridging together communities of different needs and sensibilities. In this review we will present the current status of this topic, and will also give an outlook on the vast multitude of applications, challenges, and opportunities stimulated by electronic structure calculations, making this field an important working tool and bringing together researchers of many different domains.We would like to thank Modesto Orozco and Hansel Gómez for fruitful discussions and Fátima Lucas for providing various test systems and helping with some visualizations. This work was supported by the EXTMOS\ud project, grant agreement number 646176, and the Energy oriented Centre of Excellence (EoCoE), grant agreement number 676629, funded both within the Horizon2020 framework of the European Union. This research\ud used resources of the Argonne Leadership Computing Facility at Argonne National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under contract DE-AC02-06CH11357.Peer ReviewedPostprint (author's final draft

Ab initio calculations at the MP2 level have been performed on water, methanol/water, ethanol/water, and dimethylether/water dimers and on water, methanol/water, and methanol cyclic trimers. Several properties of their hydrogen bonds have been investigated, such as interoxygen distances, O–H bond lengths, binding energies, electronic densities at hydrogen bond (HB) critical points and OH stretch vibrational frequencies. Results exhibit HB enhancements for dimers where the acceptor molecule corresponds to water (HDA dimers) as compared to dimers where the donor is water (HDD dimers). In particular, HB reinforcement depends on the number of alkyl groups bonded to the donor oxygen. For trimers, a comparison among their HB properties and those of dimers shows that HB reinforcements (as compared to isolated dimers) occurring in trimers correlate with HB reinforcements observed in (HDA dimers (as compared to (HDDs). In particular, HB properties of the cyclic water trimer are close to those of alcohol/water HDA dimers, and for the methanol cyclic trimer to that of the dimethylether/water HDA dimer. All of these results agree with an orbital interpretation of hydrogen bonding in terms of charge transfer from donor lone pairs to acceptor antibond σOH*, even if all of the HB properties in cyclic trimers may not be explained from this approach.

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