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.

scholarly journals Quantum Chemistry for Molecules at Extreme Pressure on Graphical Processing Units: Implementation of Extreme Pressure Polarizable Continuum Model

2021 ◽  
Author(s):  
Ariel Gale ◽  
Eugen Hruska ◽  
Fang Liu
Keyword(s):  
High Pressure ◽  
Quantum Chemistry ◽  
Gas Phase ◽  
Continuum Model ◽  
Polarizable Continuum Model ◽  
Medium Size ◽  
Extreme Pressure ◽  
Graphical Processing Units ◽  
Graphical Processing ◽  
Polarizable Continuum

Pressure plays essential roles in chemistry by altering structures and controlling chemical reactions. The extreme-pressure polarizable continuum model (XP-PCM) is an emerging method with an efficient quantum mechanical description of small and medium-size molecules at high pressure (on the order of GPa). However, its application to large molecular systems was previously hampered by CPU computation bottleneck: the Pauli repulsion potential unique to XP-PCM requires the evaluation of a large number of electric field integrals, resulting in significant computational overhead compared to the gas-phase or standard-pressure polarizable continuum model calculations. Here, we exploit advances in Graphical Processing Units (GPUs) to accelerate the XP-PCM integral evaluations. This enables high-pressure quantum chemistry simulation of proteins that used to be computationally intractable. We benchmarked the performance using 18 small proteins in aqueous solutions. Using a single GPU, our method evaluates the XP-PCM free energy of a protein with over 500 atoms and 4000 basis functions within half an hour. The time taken by the XP-PCM-integral evaluation is typically 1\% of the time taken for a gas-phase density functional theory (DFT) on the same system. The overall XP-PCM calculations require less computational effort than that for their gas-phase counterpart due to the improved convergence of self-consistent field iterations. Therefore, the description of the high-pressure effects with our GPU accelerated XP-PCM is feasible for any molecule tractable for gas-phase DFT calculation. We have also validated the accuracy of our method on small molecules whose properties under high pressure are known from experiments or previous theoretical studies.

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.

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