scholarly journals How accurate are approximate quantum chemical methods at modelling solute–solvent interactions in solvated clusters?

2020 ◽  
Vol 22 (7) ◽  
pp. 3855-3866 ◽  
Author(s):  
Junbo Chen ◽  
Bun Chan ◽  
Yihan Shao ◽  
Junming Ho
Keyword(s):  
Ab Initio ◽  
Quantum Chemical ◽  
Interaction Energies ◽  
Chemical Methods ◽  
Dft Methods ◽  
Solvent Interactions ◽  
Quantum Chemical Methods ◽  
Composite Methods ◽  
Wide Range

In this paper, the performance of ab initio composite methods, and a wide range of DFT methods is assessed for the calculation of interaction energies of thermal clusters of a solute in water.

The CHAL336 Benchmark Set: How Well Do Quantum-Chemical Methods Describe Chalcogen-Bonding Interactions?

2021 ◽  
Author(s):  
Nisha Mehta ◽  
Thomas Fellowes ◽  
JONATHAN WHITE ◽  
Lars Goerigk
Keyword(s):  
Density Functional ◽  
Noncovalent Interactions ◽  
Interaction Energies ◽  
Chemical Methods ◽  
Dft Methods ◽  
The Past ◽  
Quantum Chemical Methods ◽  
London Dispersion ◽  
High Level ◽  
Selection Of

<div> <div> <div> <p>We present the CHAL336 benchmark set—the most comprehensive database for the assessment of chalcogen-bonding (CB) interactions. After careful selection of suitable systems and identification of three high-level reference methods, the set comprises 336 dimers each consisting of up to 49 atoms and covers both σ- and π-hole interactions across four categories: chalcogen-chalcogen, chalcogen-π, chalcogen-halogen, and chalcogen-nitrogen interactions. In a subsequent study of DFT methods, we re- emphasize the need for using proper London-dispersion corrections when treating noncovalent interactions. We also point out that the deterioration of results and systematic overestimation of interaction energies for some dispersion-corrected DFT methods does not hint at problems with the chosen dispersion correction, but is a consequence of large density-driven errors. We conclude this work by performing the most detailed DFT benchmark study for CB interactions to date. We assess 98 variations of dispersion- corrected and -uncorrected DFT methods, and carry out a detailed analysis of 72 of them. Double-hybrid functionals are the most reliable approaches for CB interactions, and they should be used whenever computationally feasible. The best three double hybrids are SOS0-PBE0-2-D3(BJ), revDSD-PBEP86-D3(BJ), and B2NCPLYP-D3(BJ). The best hybrids in this study are ωB97M-V, PW6B95-D3(0), and PW6B95-D3(BJ). We do not recommend using any lower-rung DFT methods nor the popular B3LYP and MP2 approaches, which have been used to describe CB interactions in the past. We hope to inspire a change in computational protocols surrounding CB interactions that leads away from the commonly used, popular methods to the more robust and accurate ones recommended herein. We would also like to encourage method developers to use our set for the investigation and reduction of density-driven errors in new density functional approximations. </p> </div> </div> </div>

Predicting Feasible Organic Reaction Pathways Using Heuristically Aided Quantum Chemistry

2018 ◽  
Author(s):  
Dmitrij Rappoport ◽  
Alan Aspuru-Guzik
Keyword(s):  
Quantum Chemistry ◽  
Reaction Mechanisms ◽  
Quantum Chemical ◽  
Organic Reactions ◽  
Reaction Pathways ◽  
Empirical Knowledge ◽  
Organic Reaction ◽  
Chemical Methods ◽  
Quantum Chemical Methods ◽  
Wide Range

Studying organic reaction mechanisms using quantum chemical methods requires from the researcher an extensive knowledge of both organic chemistry and first-principles computation. The need for empirical knowledge arises because any reasonably complete exploration of the potential energy surfaces (PES) of organic reactions is computationally prohibitive. We have previously introduced the Heuristically-Aided Quantum Chemistry (HAQC) approach to modeling complex chemical reactions, which abstracts the empirical knowledge in terms of chemical heuristics—simple rules guiding the PES exploration—and combines them with structure optimizations using quantum chemical methods. The HAQC approach makes use of heuristic kinetic criteria for selecting reaction paths that are not only plausible, that is, consistent with the empirical rules of organic reactivity, but also feasible under the reaction conditions. In this work, we develop heuristic kinetic feasilibity criteria, which correctly predict feasible reaction pathways for a wide range of simple polar (substitutions, additions, and eliminations) and pericyclic organic reactions (cyclizations, sigmatropic shifts, and cycloadditions). In contrast to knowledge-based reaction mechanism prediction methods, the same kinetic heuristics are successful in classifying reaction pathways as feasible or infeasible across this diverse set of reaction mechanisms. We discuss the energy profiles of HAQC and their potential applications in machine learning of chemical reactivity.<br>

Predicting Feasible Organic Reaction Pathways Using Heuristically Aided Quantum Chemistry

2018 ◽  
Author(s):  
Dmitrij Rappoport ◽  
Alan Aspuru-Guzik
Keyword(s):  
Quantum Chemistry ◽  
Reaction Mechanisms ◽  
Quantum Chemical ◽  
Organic Reactions ◽  
Reaction Pathways ◽  
Empirical Knowledge ◽  
Organic Reaction ◽  
Chemical Methods ◽  
Quantum Chemical Methods ◽  
Wide Range

Studying organic reaction mechanisms using quantum chemical methods requires from the researcher an extensive knowledge of both organic chemistry and first-principles computation. The need for empirical knowledge arises because any reasonably complete exploration of the potential energy surfaces (PES) of organic reactions is computationally prohibitive. We have previously introduced the Heuristically-Aided Quantum Chemistry (HAQC) approach to modeling complex chemical reactions, which abstracts the empirical knowledge in terms of chemical heuristics—simple rules guiding the PES exploration—and combines them with structure optimizations using quantum chemical methods. The HAQC approach makes use of heuristic kinetic criteria for selecting reaction paths that are not only plausible, that is, consistent with the empirical rules of organic reactivity, but also feasible under the reaction conditions. In this work, we develop heuristic kinetic feasilibity criteria, which correctly predict feasible reaction pathways for a wide range of simple polar (substitutions, additions, and eliminations) and pericyclic organic reactions (cyclizations, sigmatropic shifts, and cycloadditions). In contrast to knowledge-based reaction mechanism prediction methods, the same kinetic heuristics are successful in classifying reaction pathways as feasible or infeasible across this diverse set of reaction mechanisms. We discuss the energy profiles of HAQC and their potential applications in machine learning of chemical reactivity.<br>

Study of some aliphatic ammonium ylides by semiempirical and ab initio methods: Structure and charge distribution

1980 ◽  
Vol 45 (1) ◽  
pp. 92-103 ◽  
Author(s):  
Vladimír Král ◽  
Zdeněk Arnold
Keyword(s):  
Ab Initio ◽  
Charge Distribution ◽  
Quantum Chemical ◽  
Negative Charge ◽  
Dipole Moments ◽  
Ab Initio Methods ◽  
Chemical Methods ◽  
Quantum Chemical Methods

Structure of, and charge distribution in, some aliphatic ammonium ylides were determined by quantum chemical methods (CNDO/2, INDO, MINDO/2, PCILO, ab initio-STO-3G and 4-31G bases). Non-stabilized ylides were found to have pyramidal arrangement of bonds on the ylide carbon whereas the stabilized ylides have a planar arrangement. The charge distribution in stabilized ylides indicates a significant transfer of the negative charge from the ylide carbon to the electronegative groups. The calculated dipole moments for the previously prepared compounds, as well as for the derivatives VII and X, described in this paper, agree well with the experimental value.

scholarly journals The CHAL336 Benchmark Set: How Well Do Quantum-Chemical Methods Describe Chalcogen-Bonding Interactions?

2021 ◽  
Author(s):  
Nisha Mehta ◽  
Thomas Fellowes ◽  
JONATHAN WHITE ◽  
Lars Goerigk
Keyword(s):  
Density Functional ◽  
Noncovalent Interactions ◽  
Interaction Energies ◽  
Chemical Methods ◽  
Dft Methods ◽  
The Past ◽  
Quantum Chemical Methods ◽  
London Dispersion ◽  
High Level ◽  
Selection Of

<div> <div> <div> <p>We present the CHAL336 benchmark set—the most comprehensive database for the assessment of chalcogen-bonding (CB) interactions. After careful selection of suitable systems and identification of three high-level reference methods, the set comprises 336 dimers each consisting of up to 49 atoms and covers both σ- and π-hole interactions across four categories: chalcogen-chalcogen, chalcogen-π, chalcogen-halogen, and chalcogen-nitrogen interactions. In a subsequent study of DFT methods, we re- emphasize the need for using proper London-dispersion corrections when treating noncovalent interactions. We also point out that the deterioration of results and systematic overestimation of interaction energies for some dispersion-corrected DFT methods does not hint at problems with the chosen dispersion correction, but is a consequence of large density-driven errors. We conclude this work by performing the most detailed DFT benchmark study for CB interactions to date. We assess 98 variations of dispersion- corrected and -uncorrected DFT methods, and carry out a detailed analysis of 72 of them. Double-hybrid functionals are the most reliable approaches for CB interactions, and they should be used whenever computationally feasible. The best three double hybrids are SOS0-PBE0-2-D3(BJ), revDSD-PBEP86-D3(BJ), and B2NCPLYP-D3(BJ). The best hybrids in this study are ωB97M-V, PW6B95-D3(0), and PW6B95-D3(BJ). We do not recommend using any lower-rung DFT methods nor the popular B3LYP and MP2 approaches, which have been used to describe CB interactions in the past. We hope to inspire a change in computational protocols surrounding CB interactions that leads away from the commonly used, popular methods to the more robust and accurate ones recommended herein. We would also like to encourage method developers to use our set for the investigation and reduction of density-driven errors in new density functional approximations. </p> </div> </div> </div>

scholarly journals Hydration dynamics gives the distinctive brown color in the "brown ring" nitrate test

2021 ◽  
Author(s):  
Ambar Banerjee ◽  
Michael R. Coates ◽  
Michael Odelius
Keyword(s):  
Aqueous Solution ◽  
Ab Initio ◽  
Quantum Chemical ◽  
Solution Structure ◽  
Ab Initio Molecular Dynamics ◽  
Ring Test ◽  
Chemical Methods ◽  
Aqua Complexes ◽  
Quantum Chemical Methods ◽  
Ring Complex

The brown ring test is one of the most popular and visually appealing reagent tests, commonly known to chemistry undergrads and familiar even to school students. The exact composition, mechanism and structure of the complex has been investigated for nearly a century. Recent studies have elucidated its UV-vis, EPR and Mossbauer spectra, mechanistic details and kinetics, followed by crystallization and structure determination in solid state. Nonetheless these studies were unable to address the aspects of solution structure and dynamics of the brown ring complex. We have conducted ab initio molecular dynamics simulations of the classic brown ring complex in aqueous solution. In the process from the simulation trajectory, we have identified that the classically established pseudo-octahedral [Fe(H2O)5(NO)]2+ complex is in chemical equilibrium with the square-pyramidal [Fe(H2O)4(NO)]2+ complex through the exchange of one of the coordinated H2O molecules. The dynamics in aqueous solution between the penta-aqua and tetra-aqua complexes in the brown ring system has to our knowledge never been suggested earlier. Interestingly we find, using ab initio multi-reference quantum chemical methods i.e. CASSCF/NEVPT2 and CASPT2 calculations, that the mixture of these two complexes is what gives the distinctive brown coloration to the brown ring test. We show that its UV-vis spectrum can be theoretically reproduced only by accounting these two species, and not solely the classically established [Fe(H2O)5(NO)]2+ complex. The energetics of the penta-aqua and tetra-aqua complexes is also investigated at the level of multi-reference quantum chemical methods.

SPECTROSCOPIC AND QUANTUM-CHEMICAL INVESTIGATION OF TESTOSTERONE PROPIONATE, A COMMONLY MISUSED ANABOLIC STEROID

2021 ◽  
Author(s):  
Nikola Ristivojević ◽  
◽  
Dušan Dimić ◽  
Marko Đošić ◽  
Stefan Mišić ◽  
...  
Keyword(s):  
Quantum Chemical ◽  
Density Functional ◽  
Testosterone Propionate ◽  
Anabolic Steroids ◽  
Chemical Methods ◽  
Dft Methods ◽  
Functional Theory ◽  
Quantum Chemical Methods ◽  
Td Dft ◽  
Ir And Raman

Anabolic steroids are a group of commonly counterfeit substances used by individuals who want to gain weight and muscles. Testosterone propionate (TP), an ester analog of testosterone, belongs to this group and its spectroscopic analysis is important especially when it is improperly labeled and misused. In this contribution quantum chemical methods, at the B3LYP/6- 311++G(d,p) level of theory, were applied for the prediction of the vibrational (IR and Raman) and UV-VIS spectra of TP. The applicability of the chosen level of theory was proven based on the comparison between experimental and theoretical bond lengths and angles. The most prominent bands in the IR and Raman spectra were assigned and correlated with the calculated ones. The electronic spectra were also analyzed and the assignments were made based on the Time-Dependent Density Functional Theory (TD-DFT) calculations. The orbitals included in the most intense transitions were visualized and possible solvent effects were discussed. The presented results proved the applicability of the DFT methods for the prediction of spectra that could lead to the counterfeit substances determination.

Trimethylammoniodiformylmethylide: Structure and charge distribution

1980 ◽  
Vol 45 (1) ◽  
pp. 80-91 ◽  
Author(s):  
Vladimír Král ◽  
Zdeněk Arnold
Keyword(s):  
Dipole Moment ◽  
Total Energy ◽  
Ab Initio ◽  
Charge Distribution ◽  
Quantum Chemical ◽  
Energy Minimum ◽  
Chemical Methods ◽  
Quantum Chemical Methods ◽  
Total Energy Minimum

Geometric arrangement of trimethylammoniodiformylmethylide (I) and charge distribution in this compound were calculated by quantum chemical methods (EHT, CNDO/2, INDO, PCILO, MINDO/2, ab initio). Total energy minimum was found for the arrangement If. The experimentally found dipole moment agrees very well with that calculated for this conformation.

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