Ab Initio Investigation of Ionic Hydration With the Polarizable Continuum Model

2005 ◽  
Author(s):  
Dimitrios C. Karampinos ◽  
John G. Georgiadis ◽  
Todd J. Martinez
Keyword(s):  
Ab Initio ◽  
Continuum Model ◽  
Numerical Approach ◽  
Polarizable Continuum Model ◽  
Electrostatic Problem ◽  
Ionic Hydration ◽  
Hydrated Ions ◽  
Experimental Values ◽  
Polarizable Continuum ◽  
Thermodynamics And Statistical Mechanics

The formulation of an ab initio method for the quantification of the energetics of ionic hydration is reviewed from the viewpoint of thermodynamics and statistical mechanics. The numerical approach, termed as the Polarizable Continuum Model, solves the exact quantum mechanical problem for the solute coupled with the electrostatic problem of the solvent, the latter being described as an effective continuous medium. The results show that the method can reproduce the experimental values of solvation energy for 3 cations and 3 anions by using only one adjustable parameter (scaled ionic radius) and can therefore be used in the furthter study of energetics and structure of hydrated ions.

scholarly journals High-pressure reaction profiles and activation volumes of 1,3-cyclohexadiene dimerizations computed by the extreme pressure-polarizable continuum model (XP-PCM)

2021 ◽  
Author(s):  
Bo Chen ◽  
K. N. Houk ◽  
Roberto Cammi
Keyword(s):  
High Pressure ◽  
Continuum Model ◽  
High Pressures ◽  
Polarizable Continuum Model ◽  
Activation Energies ◽  
Extreme Pressure ◽  
High Pressure Reaction ◽  
Experimental Values ◽  
Clear Shift ◽  
Polarizable Continuum

Quantum chemical calculations are reported for the thermal dimerizations of 1,3-cyclohexadiene at 1 atm and high pressures up to 6 GPa. Previous experiments [Klärner et al. Angew. Chem. Int. Ed. 1986, 25, 108], based on measured activation energies and activation volumes, suggested concerted mechanisms for the formation of the endo [4+2] cycloadduct and a [6+4]-ene adduct, and stepwise mechanisms for the formation of the exo [4+2] cycloadduct and two [2+2] cycloadducts. Computed activation enthalpies (ωB97XD, CCSD(T) and SC-NEVPT2) of plausible dimerization pathways at 1 atm agree well with the experiment activation energies and the values from previous calculations [Ess et al. J. Org. Chem. 2008, 73, 7586]. High-pressure reaction profiles, computed by the recently-developed extreme pressure-polarizable continuum model (XP-PCM), show that the reduction of reaction barrier is more profound in concerted reactions than in stepwise reactions, which is rationalized on the basis of the volume profiles of different mechanisms. A clear shift of the transition state towards the reactant by high pressure is revealed for the [6+4]-ene reaction by the calculations. The computed activation volumes by XP-PCM agree excellently with the experimental values, confirming the existence of competing mechanisms in the thermal dimerizations of 1,3-cyclohexadiene.

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