Performance of the SCC-DFTB Model for Description of Five-Membered Ring Carbohydrate Conformations: Comparison to Force Fields, High-Level Electronic Structure Methods, and Experiment

2012 ◽  
Vol 8 (7) ◽  
pp. 2412-2423 ◽  
Author(s):  
Shahidul M. Islam ◽  
Pierre-Nicholas Roy
Keyword(s):  
Electronic Structure ◽  
Force Fields ◽  
Membered Ring ◽  
Electronic Structure Methods ◽  
High Level

Solvent tunable photophysics of acridone: a quantum chemical perspective

RSC Advances ◽  
2016 ◽  
Vol 6 (22) ◽  
pp. 18530-18537 ◽  
Author(s):  
Vidisha Rai-Constapel ◽  
Christel M. Marian
Keyword(s):  
Electronic Structure ◽  
Quantum Chemistry ◽  
Quantum Chemical ◽  
Electronic Structure Methods ◽  
High Level

High-level electronic structure methods and quantum chemistry programs have been employed for a thorough investigation of the photophysics of acridone in isolated and solvated states.

scholarly journals The quest to uncover the nature of benzonitrile anion

2020 ◽  
Vol 22 (9) ◽  
pp. 5002-5010
Author(s):  
Sahil Gulania ◽  
Thomas-C. Jagau ◽  
Andrei Sanov ◽  
Anna I. Krylov
Keyword(s):  
Electronic Structure ◽  
Electronic Structure Methods ◽  
High Level

Anionic states of benzonitrile are investigated by high-level electronic structure methods.

scholarly journals Dissociative Electron Attachment in C2H via Electronic Resonances

2021 ◽  
Author(s):  
Sahil Gulania ◽  
Anna Krylov
Keyword(s):  
Electronic Structure ◽  
Chemical Vapor ◽  
Electron Attachment ◽  
Wave Functions ◽  
Cluster Method ◽  
Stable States ◽  
Resonance Wave ◽  
Electronic Structure Methods ◽  
Electronically Excited ◽  
High Level

<div> <div> <div> <div> <p>Investigation of microwave-activated CH<sub>4</sub>/H<sub>2 </sub>plasma used in chemical vapor deposition of diamond revealed the presence of electronically excited C<sub>2</sub><sup>-</sup>(B<sup>2</sup>Σ<sub>u</sub><sup>+</sup>). Using high-level electronic structure methods, we investigate electronic structure of C<sub>2</sub>H<sup>-</sup> and suggest possible routes for formation of C<sub>2</sub><sup>-</sup> in the ground (X<sup>2</sup>Σ<sub>g</sub><sup>+</sup>) and excited (B<sup>2</sup>Σ<sub>u</sub><sup>+</sup>) states via electronic resonances. To describe electronically meta-stable states, we employ the equation-of-motion coupled-cluster method augmented by the complex absorbing potential. The resonance wave-functions are analyzed using natural transition orbitals. We identified several resonances in C<sub>2</sub>H<sup>-</sup>, including the state that may lead to C<sub>2</sub><sup>-</sup>(B<sup>2</sup>Σ<sub>u</sub><sup>+</sup>). </p><p> </p> <p></p><p> </p> <p> </p> <p> </p> </div> </div> </div> </div>

scholarly journals Dissociative Electron Attachment in C2H via Electronic Resonances

2021 ◽  
Author(s):  
Sahil Gulania ◽  
Anna Krylov
Keyword(s):  
Electronic Structure ◽  
Chemical Vapor ◽  
Electron Attachment ◽  
Wave Functions ◽  
Cluster Method ◽  
Stable States ◽  
Resonance Wave ◽  
Electronic Structure Methods ◽  
Electronically Excited ◽  
High Level

<div> <div> <div> <div> <p>Investigation of microwave-activated CH<sub>4</sub>/H<sub>2 </sub>plasma used in chemical vapor deposition of diamond revealed the presence of electronically excited C<sub>2</sub><sup>-</sup>(B<sup>2</sup>Σ<sub>u</sub><sup>+</sup>). Using high-level electronic structure methods, we investigate electronic structure of C<sub>2</sub>H<sup>-</sup> and suggest possible routes for formation of C<sub>2</sub><sup>-</sup> in the ground (X<sup>2</sup>Σ<sub>g</sub><sup>+</sup>) and excited (B<sup>2</sup>Σ<sub>u</sub><sup>+</sup>) states via electronic resonances. To describe electronically meta-stable states, we employ the equation-of-motion coupled-cluster method augmented by the complex absorbing potential. The resonance wave-functions are analyzed using natural transition orbitals. We identified several resonances in C<sub>2</sub>H<sup>-</sup>, including the state that may lead to C<sub>2</sub><sup>-</sup>(B<sup>2</sup>Σ<sub>u</sub><sup>+</sup>). </p><p> </p> <p></p><p> </p> <p> </p> <p> </p> </div> </div> </div> </div>

Predicting pKa in Implicit Solvents: Current Status and Future Directions

2014 ◽  
Vol 67 (10) ◽  
pp. 1441 ◽  
Author(s):  
Junming Ho
Keyword(s):  
Free Energy ◽  
Electronic Structure ◽  
Computational Prediction ◽  
Ab Initio Molecular Dynamics ◽  
Current Status ◽  
Implicit Solvent ◽  
Energy Methods ◽  
Future Directions ◽  
Electronic Structure Methods ◽  
High Level

Computational prediction of condensed phase acidity is a topic of much interest in the field today. We introduce the methods available for predicting gas phase acidity and pKas in aqueous and non-aqueous solvents including high-level electronic structure methods, empirical linear free energy relationships (LFERs), implicit solvent methods, explicit solvent statistical free energy methods, and hybrid implicit–explicit approaches. The focus of this paper is on implicit solvent methods, and we review recent developments including new electronic structure methods, cluster-continuum schemes for calculating ionic solvation free energies, as well as address issues relating to the choice of proton solvation free energy to use with implicit solvation models, and whether thermodynamic cycles are necessary for the computation of pKas. A comparison of the scope and accuracy of implicit solvent methods with ab initio molecular dynamics free energy methods is also presented. The present status of the theory and future directions are outlined.

Performance of Electronic Structure Methods for the Description of Hückel-Möbius Interconversions in Extended π-Systems

2019 ◽  
Author(s):  
Tatiana Woller ◽  
Ambar Banerjee ◽  
Nitai Sylvetsky ◽  
Xavier Deraet ◽  
Frank De Proft ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Basis Set ◽  
Dft Methods ◽  
Molecular Switching ◽  
Wide Range ◽  
Electronic Structure Methods ◽  
Explicitly Correlated ◽  
Relative Errors ◽  
The Stability ◽  
Basis Set Expansion

<p>Expanded porphyrins provide a versatile route to molecular switching devices due to their ability to shift between several π-conjugation topologies encoding distinct properties. Taking into account its size and huge conformational flexibility, DFT remains the workhorse for modeling such extended macrocycles. Nevertheless, the stability of Hückel and Möbius conformers depends on a complex interplay of different factors, such as hydrogen bonding, p···p stacking, steric effects, ring strain and electron delocalization. As a consequence, the selection of an exchange-correlation functional for describing the energy profile of topological switches is very difficult. For these reasons, we have examined the performance of a variety of wavefunction methods and density functionals for describing the thermochemistry and kinetics of topology interconversions across a wide range of macrocycles. Especially for hexa- and heptaphyrins, the Möbius structures have a pronouncedly stronger degree of static correlation than the Hückel and figure-eight structures, and as a result the relative energies of singly-twisted structures are a challenging test for electronic structure methods. Comparison of limited orbital space full CI calculations with CCSD(T) calculations within the same active spaces shows that post-CCSD(T) correlation contributions to relative energies are very minor. At the same time, relative energies are weakly sensitive to further basis set expansion, as proven by the minor energy differences between MP2/cc-pVDZ and explicitly correlated MP2-F12/cc-pVDZ-F12 calculations. Hence, our CCSD(T) reference values are reasonably well-converged in both 1-particle and n-particle spaces. While conventional MP2 and MP3 yield very poor results, SCS-MP2 and particularly SOS-MP2 and SCS-MP3 agree to better than 1 kcal mol<sup>-1</sup> with the CCSD(T) relative energies. Regarding DFT methods, only M06-2X provides relative errors close to chemical accuracy with a RMSD of 1.2 kcal mol<sup>-1</sup>. While the original DSD-PBEP86 double hybrid performs fairly poorly for these extended p-systems, the errors drop down to 2 kcal mol<sup>-1</sup> for the revised revDSD-PBEP86-NL, again showing that same-spin MP2-like correlation has a detrimental impact on performance like the SOS-MP2 results. </p>

Ideal–Gas Thermochemical Properties for Alkanolamine and Related Species Involved in Carbon Capture Applications

2020 ◽  
Author(s):  
Nayyereh hatefi ◽  
William Smith
Keyword(s):  
Heat Capacity ◽  
Electronic Structure ◽  
Co2 Capture ◽  
Carbon Capture ◽  
Ideal Gas ◽  
Thermochemical Properties ◽  
Temperature Range ◽  
Comparison Results ◽  
Electronic Structure Methods ◽  
Protonated Forms

<div>Ideal{gas thermochemical properties (enthalpy, entropy, Gibbs energy, and heat capacity, Cp) of 49 alkanolamines potentially suitable for CO2 capture applications and their carbamate and protonated forms were calculated using two high{order electronic structure methods, G4 and G3B3 (or G3//B3LYP). We also calculate for comparison results from the commonly used B3LYP/aug-cc-pVTZ method. This data is useful for the construction of molecular{based thermodynamic models of CO2 capture processes involving these species. The Cp data for each species over the temperature range 200 K{1500 K is presented as functions of temperature in the form of NASA seven-term polynomial expressions, permitting the set of thermochemical properties to be calculated over this temperature range. The accuracy of the G3B3 and G4 results is estimated to be 1 kcal/mol and the B3LYP/aug-cc-pVTZ results are of nferior quality..</div>

Electronic Structure Benchmark Calculations of Inorganic and Biochemical Carboxylation Reactions

2018 ◽  
Author(s):  
Oscar A. Douglas-Gallardo ◽  
David A. Sáez ◽  
Stefan Vogt-Geisse ◽  
Esteban Vöhringer-Martinez
Keyword(s):  
Electronic Structure ◽  
Chemical Reactions ◽  
Density Functional ◽  
Correlation Energy ◽  
Electronic Energy ◽  
Basis Sets ◽  
Electronic Correlation ◽  
Correct Description ◽  
Carbon Dioxide Co2 ◽  
High Level

<div><div><div><p>Carboxylation reactions represent a very special class of chemical reactions that is characterized by the presence of a carbon dioxide (CO2) molecule as reactive species within its global chemical equation. These reactions work as fundamental gear to accomplish the CO2 fixation and thus to build up more complex molecules through different technological and biochemical processes. In this context, a correct description of the CO2 electronic structure turns out to be crucial to study the chemical and electronic properties associated with this kind of reactions. Here, a sys- tematic study of CO2 electronic structure and its contribution to different carboxylation reaction electronic energies has been carried out by means of several high-level ab-initio post-Hartree Fock (post-HF) and Density Functional Theory (DFT) calculations for a set of biochemistry and inorganic systems. We have found that for a correct description of the CO2 electronic correlation energy it is necessary to include post-CCSD(T) contributions (beyond the gold standard). These high-order excitations are required to properly describe the interactions of the four π-electrons as- sociated with the two degenerated π-molecular orbitals of the CO2 molecule. Likewise, our results show that in some reactions it is possible to obtain accurate reaction electronic energy values with computationally less demanding methods when the error in the electronic correlation energy com- pensates between reactants and products. Furthermore, the provided post-HF reference values allowed to validate different DFT exchange-correlation functionals combined with different basis sets for chemical reactions that are relevant in biochemical CO2 fixing enzymes.</p></div></div></div>

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