Theoretical study of small sodium–potassium alloy clusters through genetic algorithm and quantum chemical calculations

2014 ◽  
Vol 16 (19) ◽  
pp. 8895-8904 ◽  
Author(s):  
Mateus X. Silva ◽  
Breno R. L. Galvão ◽  
Jadson C. Belchior
Keyword(s):  
Quantum Chemical ◽  
Density Functional ◽  
Theoretical Study ◽  
Coupled Cluster ◽  
Functional Theory ◽  
Sodium Potassium ◽  
Cluster Calculations ◽  
Electronic Structure Methods ◽  
High Level ◽  
Alloy Clusters

Structures regarding the growth of sodium–potassium clusters obtained employing electronic structure methods—from high level coupled cluster calculations to all-electrons correlated MP2 and density functional theory.

scholarly journals A computational study for the reaction mechanism of metal-free cyanomethylation of aryl alkynoates with acetonitrile

RSC Advances ◽  
2021 ◽  
Vol 11 (30) ◽  
pp. 18246-18251
Author(s):  
Selçuk Eşsiz
Keyword(s):  
Density Functional Theory ◽  
Reaction Mechanism ◽  
Density Functional ◽  
Computational Study ◽  
Coupled Cluster ◽  
Functional Theory ◽  
Metal Free ◽  
Coupled Cluster Methods ◽  
High Level ◽  
Cluster Methods

A computational study of metal-free cyanomethylation and cyclization of aryl alkynoates with acetonitrile is carried out employing density functional theory and high-level coupled-cluster methods, such as [CCSD(T)].

Visible-light Photoresponse of Nitrogen-doped TiO2: Excited State Studies Using Time-dependent Density Functional Theory and Equation-of-Motion Coupled Cluster Methods

2010 ◽  
Vol 1263 ◽  
Author(s):  
Niranjan Govind ◽  
Roger Rousseau ◽  
Amity Andersen ◽  
Karol Kowalski
Keyword(s):  
Excited State ◽  
Density Functional ◽  
Equation Of Motion ◽  
Coupled Cluster ◽  
Functional Theory ◽  
Experimental Findings ◽  
High Level ◽  
Cluster Methods ◽  
Compare And Contrast

AbstractTo shed light on the nature of the electronic states at play in N-doped TiO2 nanoparticles, we have performed detailed ground and excited state calculations on pure and N-doped TiO2 rutile using an embedding model. We have validated our model by comparing ground-state embedded results with those obtained from periodic DFT calculations. Our results are consistent with periodic calculations. Using this embedding model we have performed B3LYP based TDDFT calculations of the excited state spectrum. We have also studied the lowest excitations using high-level equation-of-motion coupled cluster (EOMCC) approaches involving all single and inter-band double excitations. We compare and contrast the nature of the excitations in detail for the pure and doped systems using these calculations. Our calculations indicate a lowering of the bandgap and confirm the role of the N3- states on the UV/Vis spectrum of N-doped TiO2 rutile supported by experimental findings.

scholarly journals Quantum chemical accuracy from density functional approximations via machine learning

2019 ◽  
Author(s):  
Mihail Bogojeski ◽  
Leslie Vogt-Maranto ◽  
Mark E. Tuckerman ◽  
Klaus-Robert Mueller ◽  
Kieron Burke
Keyword(s):  
Machine Learning ◽  
Quantum Chemical ◽  
Density Functional ◽  
Md Simulations ◽  
Training Data ◽  
Coupled Cluster ◽  
Functional Theory ◽  
Computational Costs ◽  
Standard Tool ◽  
Cluster Accuracy

<div> <div> <p>Kohn-Sham density functional theory (DFT) is a standard tool in most branches of chemistry, but accuracies for many molecules are limited to 2-3 kcal/mol with presently-available functionals. <i>Ab initio</i> methods, such as coupled-cluster, routinely produce much higher accuracy, but computational costs limit their application to small molecules. In this paper, we leverage machine learning to calculate coupled-cluster energies from DFT densities, reaching quantum chemical accuracy (errors below 1 kcal/mol) on test data. Moreover, density-based ∆-learning (learning only the correction to a standard DFT calculation, termed ∆-DFT) significantly reduces the amount of training data required, particularly when molecular symmetries are included. The robustness of ∆-DFT is highlighted by correcting "on the fly" DFT-based molecular dynamics (MD) simulations of resorcinol (C<sub>6</sub>H<sub>4</sub>(OH)<sub>2</sub>) to obtain MD trajectories with coupled-cluster accuracy. We conclude, therefore, that ∆-DFT facilitates running gas-phase MD simulations with quantum chemical accuracy, even for strained geometries and conformer changes where standard DFT fails.</p> </div> </div>

scholarly journals Theoretical Study on Structure and Electronic Properties of 4H-Cyclopenta[2,1-b,3;4-b’]dithiopene S-oxide and Its CCl2 and CF2 Bridged Derivatives

2015 ◽  
Vol 15 (1) ◽  
pp. 93-100 ◽  
Author(s):  
Banjo Semire ◽  
Olusegun Ayobami Odunola
Keyword(s):  
Density Functional Theory ◽  
Thermodynamic Properties ◽  
Quantum Chemical ◽  
Density Functional ◽  
Theoretical Study ◽  
Functional Theory ◽  
Td Dft ◽  
Moller Plesset ◽  
Semi Empirical ◽  
Good Agreement

Quantum chemical calculations using semi-empirical, ab initio, density functional theory (DFT) and Møller plesset (MP2) methods were performed on 4H-Cyclopenta[2,1-b,3;4-b’]dithiopene S-oxide derivatives (i.e. bridged dithiophene S-oxides, BTOs). The geometries, stabilities, electronic and thermodynamic properties of the compounds were studied. The thermodynamic parameters calculated at PM3 were in good agreement with those calculated at B3LYP/6-31G(d) level. The band gap energies calculated at B3LYP/6-31G(d) level for the BTOs were lower than the un-substituted trithiophene but higher than 4H-Cyclopenta[2,1-b,3;4-b’]dithiopene. The absorption λmax calculated using TD-DFT was shifted to longer wavelength by successive replacement of methylene hydrogens of BTO by chlorine and fluorine atoms.

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