Seminar

Seminar

[세미나공지] 4월 22일(수)

  • POSTED DATE : 2015-04-22
  • WRITER : 관리자
  • HIT : 2806
  • DATE : 2015-04-22
  • PLACE : 화학관 1층 330118호

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제  목 :  Novel Approach for Condensed-Phase Thermochemistry: Proposal and Applications of Harmonic Solvation Model (HSM)

연  사 :Hiromi Nakai 교수님 (와세다대학교)

 

일  시 : 2015년 4월 22(수) 오전 11시


장  소 : 화학관 1층 강의실 (330118호실)

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Novel Approach for Condensed-Phase Thermochemistry: Proposal and Applications of Harmonic Solvation Model (HSM)



  Over the 90 years’ history, quantum chemistry has been well developed and become a systematic treatment to evaluate a molecule’s electronic energy Eelec, and molecular properties such as geometric parameters and vibrational frequencies. Furthermore, the use of statistical mechanics under the ideal gas model (IGM) assumption enables estimation of the Gibbs energy G, which involves the enthalpy H and entropy S of a gaseous molecule.


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  The subscripts elec, vib, rot, and trans denote electronic, vibrational, rotational, and translational contributions, respectively, to the energy and entropy. In many cases, except at extremely high/low temperatures and/or pressures, the IGM works well and reasonably reproduces the thermodynamic properties.


  The situation is more complicated in the liquid phase. Much effort has been devoted to developing solvation models to describe electrostatic interactions and non-electrostatic interactions such as Pauli repulsion, dispersion, and cavity formation energy. The self-consistent reaction field (SCRF) formalism is one of the most widely used models; it mainly focuses on the solvation free energy. The contribution of solvent effects obtained using the SCRF is normally added to the electronic energy using standard quantum chemical programs. Other contributions to the enthalpy and entropy are evaluated using the formalism based on the IGM.


  However, the molecular motion in the liquid phase is remarkably different from that in the gas phase. As a result, the IGM treatment fails to reproduce the condensed-phase thermochemistry and occasionally lead to unphysical behaviours. We have recently an alternative approach to calculate thermochemical parameters in the condensed phase, in particular, in the liquid phase.[1,2] The model represents translational and rotational motions of a solute as vibrations interacting with a cavity wall of solvents and treats all the degrees of freedom for nuclear motion as harmonic vibrations. Thus, we call it the harmonic solvation model (HSM). The computational cost of HSM is comparable with the conventional calculations for enthalpy, entropy, and Gibbs energy using the ideal gas model (IGM): namely, geometry optimization and frequency analysis are required in the quantum chemical calculations.



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The accuracy of the HSM is confirmed by applying to the standard formation reaction of liquid water, combustion reactions of liquid organic molecules, vapor–liquid equilibration, and dissolution of gaseous molecules. For example, the boiling point of water was reasonably described by the present HSM treatment, while the conventional IGM treatment failed to obtain a crossing of the two Gibbs energy curves for gaseous and liquid water (Fig. 1).



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[1] “Quantum chemical approach for condensed-phase thermochemistry: Proposal of a harmonic solvation model”, H. Nakai, A. Ishikawa, J. Chem. Phys., 141 (17), 174106 (9 pages) (2014). (DOI: 10.1063/1.4900629)


[2] “Quantum chemical approach for condensed-phase thermochemistry (II): Applications to formation and combustion reactions of liquid organic molecules”, A. Ishikawa, H. Nakai, Chem. Phys. Letters, 624, 6–11 (2015). (DOI: 10.1016/j.cplett.2015.01.054)