scholarly journals Pinacolone-Alcohol Gas-Phase Solvation Balances as Experimental Dispersion Benchmarks

Molecules ◽  
2020 ◽  
Vol 25 (21) ◽  
pp. 5095
Author(s):  
Charlotte Zimmermann ◽  
Taija L. Fischer ◽  
Martin A. Suhm
Keyword(s):  
Supersonic Jet ◽  
Zero Point ◽  
Energy Difference ◽  
Density Functionals ◽  
Harmonic Frequency ◽  
Point Energy ◽  
Electron Pairs ◽  
London Dispersion ◽  
London Dispersion Forces ◽  
Experimental Dispersion

The influence of distant London dispersion forces on the docking preference of alcohols of different size between the two lone electron pairs of the carbonyl group in pinacolone was explored by infrared spectroscopy of the OH stretching fundamental in supersonic jet expansions of 1:1 solvate complexes. Experimentally, no pronounced tendency of the alcohol to switch from the methyl to the bulkier tert-butyl side with increasing size was found. In all cases, methyl docking dominates by at least a factor of two, whereas DFT-optimized structures suggest a very close balance for the larger alcohols, once corrected by CCSD(T) relative electronic energies. Together with inconsistencies when switching from a C4 to a C5 alcohol, this points at deficiencies of the investigated B3LYP and in particular TPSS functionals even after dispersion correction, which cannot be blamed on zero point energy effects. The search for density functionals which describe the harmonic frequency shift, the structural change and the energy difference between the docking isomers of larger alcohols to unsymmetric ketones in a satisfactory way is open.

scholarly journals Pinacolone-Alcohol Gas-Phase Solvation Balances as Experimental Dispersion Benchmarks

2020 ◽  
Author(s):  
Charlotte Zimmermann ◽  
Taija L. Fischer ◽  
Martin A. Suhm
Keyword(s):  
Supersonic Jet ◽  
Zero Point ◽  
Energy Difference ◽  
Density Functionals ◽  
Harmonic Frequency ◽  
Point Energy ◽  
Electron Pairs ◽  
London Dispersion ◽  
London Dispersion Forces ◽  
Experimental Dispersion

The influence of distant London dispersion forces on the docking preference of alcohols of different size between the two lone electron pairs of the carbonyl group in pinacolone is explored by infrared spectroscopy of the OH stretching fundamental in supersonic jet expansions of 1:1 solvate complexes. Experimentally, no pronounced tendency of the alcohol to switch from the methyl to the bulkier tert-butyl side with increasing size is found. In all cases, methyl docking dominates by at least a factor of two, whereas DFT-optimized structures suggest a very close balance for the larger alcohols, once corrected by CCSD(T) relative electronic energies. Together with inconsistencies when switching from a C4 to a C5 alcohol, this points at deficiencies of the investigated B3LYP and in particular TPSS functionals even after dispersion correction, which cannot be blamed on zero point energy effects. The search for density functionals which describe the harmonic frequency shift, the structural change and the energy difference between the docking isomers of larger alcohols to unsymmetric ketones in a satisfactory way is open.

scholarly journals London dispersion forces without density distortion: a path to first principles inclusion in density functional theory

2020 ◽  
Vol 224 ◽  
pp. 145-165
Author(s):  
Derk Pieter Kooi ◽  
Paola Gori-Giorgi
Keyword(s):  
Ground State ◽  
First Principles ◽  
Density Functional ◽  
Dispersion Forces ◽  
Density Functionals ◽  
Functional Theory ◽  
Exchange Correlation ◽  
State Densities ◽  
London Dispersion ◽  
London Dispersion Forces

We analyse a path to construct density functionals for the dispersion interaction energy from an expression in terms of the ground state densities and exchange–correlation holes of the isolated fragments.

scholarly journals The Role of Vibrational Anharmonicity in the Computational Study of Thermal Spin Crossover

2019 ◽  
Vol 5 (3) ◽  
pp. 49 ◽  
Author(s):  
Jianfang Wu ◽  
Carmen Sousa ◽  
Coen de Graaf
Keyword(s):  
Computational Chemistry ◽  
Spin Crossover ◽  
Computational Study ◽  
Accurate Determination ◽  
Zero Point ◽  
Energy Difference ◽  
Electronic Energy ◽  
Point Energy ◽  
A Minor ◽  
The Impact

Spin crossover in transition metal complexes can be studied in great detail with computational chemistry. Over the years, the understanding has grown that the relative stability of high-spin (HS) versus low-spin (LS) states is a subtle balance of many factors that all need to be taken into account for a reliable description. Among the different contributions, the zero-point energy (ZPE) and the entropy play key roles. These quantities are usually calculated assuming a harmonic oscillator model for the molecular vibrations. We investigated the impact of including anharmonic corrections on the ZPE and the entropy and indirectly on the critical temperature of spin crossover. As test systems, we used a set of ten Fe(II) complexes and one Fe(III) complex, covering different coordination modes (mono-, bi-, and tri-dentate ligands), decreasing coordination number upon spin crossover, coordination by second- and third-row atoms, and changes in the oxidation state. The results show that the anharmonicity has a measurable effect, but it is in general rather small, and tendencies are not easily recognized. As a conclusion, we put forward that for high precision results, one should be aware of the anharmonic effects, but as long as computational chemistry is still struggling with other larger factors like the influence of the environment and the accurate determination of the electronic energy difference between HS and LS, the anharmonicity of the vibrational modes is a minor concern.

Electron transfer in mixed-valence biferrocenium salts: effect of zero-point energy difference and pronounced anion dependence

1991 ◽  
Vol 30 (11) ◽  
pp. 2457-2462 ◽  
Author(s):  
Teng Yuan. Dong ◽  
Chi Chang. Schei ◽  
Tsui Ling. Hsu ◽  
Shyi Long. Lee ◽  
Shiang Jin. Li
Keyword(s):  
Electron Transfer ◽  
Mixed Valence ◽  
Zero Point ◽  
Energy Difference ◽  
Zero Point Energy ◽  
Point Energy

On the Use of Quantum Thermal Bath in Unimolecular Fragmentation Simulations

2019 ◽  
Author(s):  
Riccardo Spezia ◽  
Hichem Dammak
Keyword(s):  
Degrees Of Freedom ◽  
Molecular Simulations ◽  
Zero Point ◽  
Thermal Bath ◽  
Unimolecular Dissociation ◽  
Point Energy ◽  
Rotational Degrees Of Freedom ◽  
The Difference ◽  
Nuclear Effects

<div> <div> <div> <p>In the present work we have investigated the possibility of using the Quantum Thermal Bath (QTB) method in molecular simulations of unimolecular dissociation processes. Notably, QTB is aimed in introducing quantum nuclear effects with a com- putational time which is basically the same as in newtonian simulations. At this end we have considered the model fragmentation of CH4 for which an analytical function is present in the literature. Moreover, based on the same model a microcanonical algorithm which monitor zero-point energy of products, and eventually modifies tra- jectories, was recently proposed. We have thus compared classical and quantum rate constant with these different models. QTB seems to correctly reproduce some quantum features, in particular the difference between classical and quantum activation energies, making it a promising method to study unimolecular fragmentation of much complex systems with molecular simulations. The role of QTB thermostat on rotational degrees of freedom is also analyzed and discussed. </p> </div> </div> </div>

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