Interactions of dimethyl sulfoxide with carbon dioxide and water molecules which induce 18 significantly stable complexes are thoroughly investigated. An addition of CO 2 or H 2 O molecules into the DMSOÁ Á Á1CO 2 and DMSOÁ Á Á1H 2 O systems leads to an increase in the stability of the resulting complexes, in which it is larger for a H 2 O addition than a CO 2 . The overall stabilization energy of the DMSOÁ Á Á1,2CO 2 is mainly contributed by the S=OÁ Á ÁC Lewis acid-base interaction, whereas the O − HÁ Á ÁO hydrogen bond plays a significant role in stabilizing complexes of DMSOÁ Á Á1,2H 2 O and DMSOÁ Á Á1CO 2 Á Á Á1H 2 O. Remarkably, the complexes of DMSOÁ Á Á2H 2 O are found to be more stable than DMSOÁ Á Á1CO 2 Á Á Á1H 2 O and DMSOÁ Á Á2CO 2 . The level of the cooperativity of multiple interactions in ternary complexes tends to decrease in going from DMSOÁ Á Á2H 2 O to DMSOÁ Á Á1CO 2 Á Á Á1H 2 O and finally to DMSOÁ Á Á2CO 2 . It is generally found that the red shift of the O − H bond involved in an O − HÁ Á ÁO hydrogen bond increases while the blue shift of a C − H bond in a C − HÁ Á ÁO hydrogen bond decreases when a cooperative effect occurs in ternary complexes as compared to those of the corresponding binary complexes.

The relative energies of different phases or polymorphs of molecular solids can be small, less than a kiloJoule/mol. Reliable description of such energy differences requires high quality treatment of electron correlations, typically beyond that achievable by routinely applicable density functional theory approximations (DFT). At the same time, high-level wave function theory is currently too computationally expensive. Methods employing intermediate level of approximations, such as Møller-Plesset (MP) perturbation theory and the random-phase approximation (RPA) are potentially useful. However, their development and application for molecular solids has been impeded by the scarcity of necessary benchmark data for these systems. In this work we employ the coupled-clusters method with singles, doubles and perturbative triples (CCSD(T)) to obtain a reference-quality many-body expansion of the binding energy of four crystalline hydrocarbons with a varying π-electron character: ethane, ethene, and cubic and orthorhombic forms of acetylene. The binding energy is resolved into explicit dimer, trimer, and tetramer contributions, which facilitates the analysis of errors in the approximate approaches. With the newly generated benchmark data we test the accuracy of MP2 and non-self-consistent RPA. We find that both of the methods poorly describe the non-additive many-body interactions in closely packed clusters. Using different DFT input states for RPA leads to similar total binding energies, but the many-body components strongly depend on the choice of the exchange-correlation functional.