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

Abstract

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 was decomposed into contributions and . is the solvation free energy of the solute with a fixed electron density and is the residual free energy due to the electron density polarisation in solution. We, further, decomposed the free energies due to electron density fluctuations in aromatic solutes in aqueous solutions into contributions from and orbitals. We note, however, that the decompositions will not be validated when the polarisations of orbitals seriously couple with those of orbitals. In this paper, we study a correlation matrix between polarisations of and 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 transfers between the orbitals lying in the HOMO–LUMO region. Thus, the polarisation of electrons hardly couples with that from orbitals, which justifies our decomposition analyses.

Keywords:

• QM/MM-ER
• second-order perturbation theory
• solvation free energy
• XH/ interaction
• correlation matrix

Notes

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work is supported by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) under the Grant-in-Aid for Scientific Research on Innovative Areas [grant number 23118701]; the Japan Society for the Promotion of Science (JSPS) under the Grant-in-Aid for Challenging Exploratory Research [grant number 25620004]; the Nanoscience Program and the Computational Materials Science Initiative of the Next-Generation Supercomputing Project (No. hp160007, hp160013, hp160019 and hp160214); JSPS Research Fellowships for Young Scientists [grant number JP16J02027].