Intermolecular interaction network in liquid acetone

Molecular dynamics simulations, employing the transferable potentials for phase equilibria-united atom force field, have been performed to explore the structural features of liquid acetone. Topological and dynamical network analyses have been performed on the intermolecular interaction (IMI) networks, which are constructed based on a set of pair energy cutoffs. Topological analysis revealed that the acetone pairs interacting stronger than -10 kJ/mol exist as isolated pairs in a sense that the members of the pair do not interact with other molecules with an energy smaller than -10 kJ/mol. As such, those strongly interacting pairs do not constitute a three-dimensional extended network. As the pair interaction energy cutoff becomes larger than -10 kJ/mol, the IMI network starts to become a three-dimensional extended network and its connectivity increases gradually. Dynamical analysis revealed that the decay function for intermolecular interaction lifetimes is characterized by a nonexponential decay for all the IMI networks such that it decays faster at short-times in comparison to the longer-times. Yet, the duration of the intermolecular interactions can go beyond 1.0 ps for the pairs with the interaction energies larger than -6 kJ/mol. Furthermore, the orientational correlations in the liquid acetone have been examined for a more detailed picture of its structure. It is clearly shown that as the distance between the carbonyl carbons of the two acetones gets smaller, (i) they tend to adopt an anti-parallel dipole orientation, (ii) the planes of the acetones tend to adopt a parallel orientation, and, (iii) such acetone pairs particularly interact more strongly. In the light of these findings, two dimeric structures, stack-type and planar-type, are highlighted. Using density functional theory (DFT) at the mPW2PLYP/def2-TZVP level, the interaction energy in the gas-phase is computed to be -19.85 kJ/mol for the stack-type dimer, which is more stable than the planar-type dimer by 7.7 kJ/mol. Both the gas-phase DFT interaction energy and the computed acetone dipole moment, 2.97 D, are in great agreement with the corresponding experimental data. Furthermore, in accordance with the gas-phase results, the stack-type dimers are found to be more stable than the planar-type dimers also in the liquid-phase as revealed from both the liquid-phase DFT interaction energies and the MD based mean interaction energies. Finally, trimeric structure search in the simulated liquid acetone revealed that of all trimers, 94% belongs to the chain-like trimers, while the remaining 6% belongs to the cyclic trimers. (C) 2021 Elsevier B.V. All rights reserved.