A QM/MM study on the correlation between the polarisations of π and σ electrons in a hydrated benzene

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In a recent work, we performed free-energy analyses for hydration of benzene by conducting QM/MM-ER simulations, where the total solvation free energy Δμ was decomposed into contributions Δμ and δμ (Δμ = Δμ + δμ). Δμ is the solvation free energy of the solute with a fixed electron density and δμ is the residual free energy due to the electron density polarisation in solution. We, further, decomposed the free energies δμ due to electron density fluctuations in aromatic solutes in aqueous solutions into contributions from π and σ orbitals. We note, however, that the decompositions will not be validated when the polarisations of π orbitals seriously couple with those of σ orbitals. In this paper, we study a correlation matrix between polarisations of π and σ orbitals through QM/MM simulations to assess the coupling strength among the orbitals. We found that the electron density polarisation is dominated by the polarisation arising from π - π * transfers between the orbitals lying in the HOMO-LUMO region. Thus, the polarisation of π electrons hardly couples with that from σ orbitals, which justifies our decomposition analyses.

Original languageEnglish
Pages (from-to)1209-1217
Number of pages9
JournalMolecular Simulation
Issue number13-16
Publication statusPublished - 2017


  • Correlation matrix
  • QM/MM-ER
  • Second-order perturbation theory
  • Solvation free energy
  • XH/π interaction

ASJC Scopus subject areas

  • Chemistry(all)
  • Information Systems
  • Modelling and Simulation
  • Chemical Engineering(all)
  • Materials Science(all)
  • Condensed Matter Physics


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