Electronic Energy and Local Property Errors at QTAIM Critical Points while Climbing Perdew’s Ladder of Density-Functional Approximations

2021 ◽  
Author(s):  
Éric Brémond ◽  
Vincent Tognetti ◽  
Henry Chermette ◽  
Juan Carlos Sancho-García ◽  
Laurent Joubert ◽  
...  
Keyword(s):  
Critical Points ◽  
Density Functional ◽  
Local Property ◽  
Electronic Energy

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>

Quantum Mechanical Investigation of Geometrical Structure and Dynamic Behavior of h-BNNT (9,9-5) and h-AlNNT (9,9-5)Single-Walled Nanotubes: NBO Analysis

2019 ◽  
Vol 16 (9) ◽  
pp. 705-717
Author(s):  
Mehrnoosh Khaleghian ◽  
Fatemeh Azarakhshi
Keyword(s):  
Carbon Nanotubes ◽  
Density Functional ◽  
Structural Parameters ◽  
Energy Levels ◽  
Nbo Analysis ◽  
Electronic Energy ◽  
Boron Nitride Nanotubes ◽  
Basis Set ◽  
B3lyp Method ◽  
Mechanical Investigation

In the present research, B45H36N45 Born Nitride (9,9) nanotube (BNNT) and Al45H36N45 Aluminum nitride (9,9) nanotube (AlNNT) have been studied, both having the same length of 5 angstroms. The main reason for choosing boron nitride nanotubes is their interesting properties compared with carbon nanotubes. For example, resistance to oxidation at high temperatures, chemical and thermal stability higher rather than carbon nanotubes and conductivity in these nanotubes, unlike carbon nanotubes, does not depend on the type of nanotube chirality. The method used in this study is the density functional theory (DFT) at Becke3, Lee-Yang-Parr (B3LYP) method and 6-31G* basis set for all the calculations. At first, the samples were simulated and then the optimized structure was obtained using Gaussian 09 software. The structural parameters of each nanotube were determined in 5 layers. Frequency calculations in order to extract the thermodynamic parameters and natural bond orbital (NBO) calculations have been performed to evaluate the electron density and electrostatic environment of different layers, energy levels and related parameters, such as ionization energy and electronic energy, bond gap energy and the share of hybrid orbitals of different layers.

scholarly journals Benchmarking the Fluxional Processes of Organometallic Piano-Stool Complexes

Molecules ◽  
2021 ◽  
Vol 26 (8) ◽  
pp. 2310
Author(s):  
Nathan C. Frey ◽  
Eric Van Dornshuld ◽  
Charles Edwin Webster
Keyword(s):  
Transition Metals ◽  
Density Functional ◽  
Chemical Shifts ◽  
Transition States ◽  
Electronic Energy ◽  
Basis Set ◽  
Composite Approach ◽  
Temperature Regimes ◽  
Correlation Consistent Composite Approach ◽  
Correlation Consistent

The correlation consistent Composite Approach for transition metals (ccCA-TM) and density functional theory (DFT) computations have been applied to investigate the fluxional mechanisms of cyclooctatetraene tricarbonyl chromium ((COT)Cr(CO)3) and 1,3,5,7-tetramethylcyclooctatetraene tricarbonyl chromium, molybdenum, and tungsten ((TMCOT)M(CO)3 (M = Cr, Mo, and W)) complexes. The geometries of (COT)Cr(CO)3 were fully characterized with the PBEPBE, PBE0, B3LYP, and B97-1 functionals with various basis set/ECP combinations, while all investigated (TMCOT)M(CO)3 complexes were fully characterized with the PBEPBE, PBE0, and B3LYP methods. The energetics of the fluxional dynamics of (COT)Cr(CO)3 were examined using the correlation consistent Composite Approach for transition metals (ccCA-TM) to provide reliable energy benchmarks for corresponding DFT results. The PBE0/BS1 results are in semiquantitative agreement with the ccCA-TM results. Various transition states were identified for the fluxional processes of (COT)Cr(CO)3. The PBEPBE/BS1 energetics indicate that the 1,2-shift is the lowest energy fluxional process, while the B3LYP/BS1 energetics (where BS1 = H, C, O: 6-31G(d′); M: mod-LANL2DZ(f)-ECP) indicate the 1,3-shift having a lower electronic energy of activation than the 1,2-shift by 2.9 kcal mol−1. Notably, PBE0/BS1 describes the (CO)3 rotation to be the lowest energy process, followed by the 1,3-shift. Six transition states have been identified in the fluxional processes of each of the (TMCOT)M(CO)3 complexes (except for (TMCOT)W(CO)3), two of which are 1,2-shift transition states. The lowest-energy fluxional process of each (TMCOT)M(CO)3 complex (computed with the PBE0 functional) has a ΔG‡ of 12.6, 12.8, and 13.2 kcal mol−1 for Cr, Mo, and W complexes, respectively. Good agreement was observed between the experimental and computed 1H-NMR and 13C-NMR chemical shifts for (TMCOT)Cr(CO)3 and (TMCOT)Mo(CO)3 at three different temperature regimes, with coalescence of chemically equivalent groups at higher temperatures.

Developing orbital-free quantum crystallography: the local potentials and associated partial charge densities

2021 ◽  
Vol 77 (4) ◽  
Author(s):  
Vladimir Tsirelson ◽  
Adam Stash
Keyword(s):  
Density Functional Theory ◽  
Electron Density ◽  
Density Functional ◽  
Electronic Energy ◽  
Physical Content ◽  
Functional Theory ◽  
Orbital Free ◽  
The One ◽  
Physical And Chemical ◽  
Quantum Crystallography

This work extends the orbital-free density functional theory to the field of quantum crystallography. The total electronic energy is decomposed into electrostatic, exchange, Weizsacker and Pauli components on the basis of physically grounded arguments. Then, the one-electron Euler equation is re-written through corresponding potentials, which have clear physical and chemical meaning. Partial electron densities related with these potentials by the Poisson equation are also defined. All these functions were analyzed from viewpoint of their physical content and limits of applicability. Then, they were expressed in terms of experimental electron density and its derivatives using the orbital-free density functional theory approximations, and applied to the study of chemical bonding in a heteromolecular crystal of ammonium hydrooxalate oxalic acid dihydrate. It is demonstrated that this approach allows the electron density to be decomposed into physically meaningful components associated with electrostatics, exchange, and spin-independent wave properties of electrons or with their combinations in a crystal. Therefore, the bonding information about a crystal that was previously unavailable for X-ray diffraction analysis can be now obtained.

scholarly journals Ground State Properties of the Wide Band Gap Semiconductor Beryllium Sulfide (BeS)

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6128
Author(s):  
Blaise A. Ayirizia ◽  
Janee’ S. Brumfield ◽  
Yuriy Malozovsky ◽  
Diola Bagayoko
Keyword(s):  
Band Gap ◽  
Lattice Constant ◽  
Ground State ◽  
Density Functional ◽  
Local Density ◽  
Wide Band ◽  
Electronic Energy ◽  
Computational Method ◽  
Energy Bands ◽  
Ground State Properties

We report the results from self-consistent calculations of electronic, transport, and bulk properties of beryllium sulfide (BeS) in the zinc-blende phase, and employed an ab-initio local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO). We obtained the ground state properties of zb-BeS with the Bagayoko, Zhao, and Williams (BZW) computational method, as enhanced by Ekuma and Franklin (BZW-EF). Our findings include the electronic energy bands, the total (DOS) and partial (pDOS) densities of states, electron and hole effective masses, the equilibrium lattice constant, and the bulk modulus. The calculated band structure clearly shows that zb-BeS has an indirect energy band gap of 5.436 eV, from Γ to a point between Γ and X, for an experimental lattice constant of 4.863 Å. This is in excellent agreement with the experiment, unlike the findings of more than 15 previous density functional theory (DFT) calculations that did not perform the generalized minimization of the energy functional, required by the second DFT theorem, which is inherent to the implementation of our BZW-EF method.

scholarly journals TD-DFT: An Exploration of the Energies and Structures of Crystal Violet and a Variety of Cr(III) Complex Ions

2021 ◽  
Author(s):  
◽  
Richard Kleingeld
Keyword(s):  
Electron Density ◽  
Density Functional ◽  
Computational Cost ◽  
Empty Space ◽  
Electronic Energy ◽  
Computational Method ◽  
Complex Ions ◽  
Phase Measurements ◽  
Td Dft ◽  
Electron Correlation Effects

<p>Spectroscopy is the science of utilising light in order to divine information about a molecule or system of molecules. Specifically, the absorption, emission, and scattering of different wavelengths of light can provide data about bond strength, bond order, vibrational frequency, and excitation energy [1, 2]. As the wavelength and therefore energy of the incident photons can be set by the instrument, the exact energies of absorbance or emission of the molecule can be measured. This data can be gathered experimentally using specialised equipment however some molecules resist synthesis, and so a wealth of data about many theoretically possible species eludes us. We may also want to isolate the molecule in “empty space” whereas “gas phase” measurements are not always possible. This is one place where computational chemistry comes to the fore. Using an appropriate computational method such as density functional theory (DFT), data can be theoretically derived and calculated for many interesting areas of chemistry. DFT is a computational method based on the findings of Hohenberg and Kohn in 1964 that the ground state electronic energy of a system can be determined completely by the electron density [3-6]. This means that it has a considerably higher efficiency as a computational method compared to the wave function approach, where the number of variables increases exponentially as your system increases in size, as the electron density has the same number of variables regardless of the size of the system [7]. The use of an appropriate functional to map the electron density and the energy is one of the vital choices in utilising this method, but if chosen well can provide good results with a much lower computational cost than other methods, while still accounting for electron correlation effects [8]. It has become a very popular method due to its versatility and generally good accuracy with relatively low computational expense when compared to ab initio methods [9].</p>

scholarly journals Physiochemical, molecular docking, and pharmacokinetic studies of Naproxen and its modified derivatives based on DFT

2018 ◽  
Vol 6 (09) ◽  
Author(s):  
Monir Uzzaman ◽  
Mohammed Jabedul Hoque
Keyword(s):  
Molecular Docking ◽  
Binding Affinity ◽  
Density Functional ◽  
Parent Drug ◽  
Electronic Energy ◽  
Frontier Molecular Orbital ◽  
Pharmacokinetic Studies ◽  
Biochemical Interaction ◽  
Gibb’S Free Energy ◽  
Anti Inflammation

Naproxen (N) is a member of nonsteroidal anti-inflammation drug and widely used as an analgesic, antipyretic, and anti-inflammation agent. In this investigation, the inherent stability and biochemical interaction of Naproxen and its related molecules have been studied. Density functional theory (DFT) with B3LYP/ 6-31G (d, p) has been employed to optimize the structures. Frontier molecular orbital features (HOMO-LUMO gap, hardness, softness), dipole moment, electrostatic potential and thermodynamic properties (electronic energy, enthalpy, Gibb’s free energy) of these optimized drugs are investigated. Molecular docking has been performed against prostaglandin H2 (PGH2) synthase protein 5F19 to search the binding affinity and mode(s) of all compounds. It is found that, all compounds are thermodynamically stable; some of them are chemically more reactive and show better binding affinity than the parent drug. ADMET calculations predict the improved pharmacokinetic properties of all compounds. Finally, this study can be helpful for the design of new analgesic, antipyretic drug.

Density Functional Calculation of Property of the (1 0 0) Surface of γ-Pu

2010 ◽  
Author(s):  
Rusong Li ◽  
Bin He ◽  
Quanhu Zhang ◽  
Qianwei Du
Keyword(s):  
Fermi Level ◽  
Density Functional ◽  
Atomic Orbital ◽  
Relativistic Effects ◽  
Local Property ◽  
Density Functional Calculation ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Surface Corrosion ◽  
Generate Surface

Pu material can generate surface corrosion and self-radiation effect during storage, leading to the creation and recoil of uranium and helium ions, which produce defects through displacement cascades, these self-irradiation defects tend to change plutonium properties. To study these aging behavior, calculations at the spin unrestricted generalized gradient approximation (GGA) level of density functional theory (DFT) have been performed using the DMol3 programs. Relativistic effects, such as mass-velocity, Darwin term, are considered in this code. Some conclusions are draw as follows: 1) Band structure of the (100) surface of γ-Pu is very narrow around the Fermi level, showing that the eigenstate of this level is mainly composed of local atomic orbital, the local property of electrons in this band is very strong, while the band around the Fermi level is mainly constituted by 5f narrow band; 2) DOS of the (100) surface of γ-Pu are mainly composed of the density of states in −48–41eV, −23–16eV, −3–2eV; 3) Contribution of s shell to the total DOS is mainly distributed in the first interval, and p shell is mainly in the second interval, while d and f shells are mainly in the third interval.

The “Decisive” Role for Secondary Coordination Sphere Nucleophiles on Hydrogen Atom Transfer (HAT) Reactions: Does It Exist and What Is Its Origin?

2020 ◽  
Author(s):  
Yumiao Ma ◽  
Yishan Li
Keyword(s):  
Hydrogen Atom ◽  
Density Functional ◽  
Decisive Role ◽  
Electronic Energy ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Major Contributor ◽  
Functional Theory ◽  
Secondary Coordination Sphere ◽  
Stabilization Effect

Although it has been reported that some radical reactions are possibly promoted by external ions, the origin of this phenomenon is unclear. In this work, several hydrogen atom transfer (HAT) reactions in the presence of anions were studied by density functional theory (DFT) calculations, electronic structure analysis and other methods, and it is concluded that both the electrostatic interaction and polarization of the transition state (TS) by the electric field generated by anions play a fundamental role in the TS stabilization effect, whereas the “charge shift bonding” that was previously presumed to be a major contributor is ruled out. Although the stabilization toward TSs in terms of electronic energy (and thus enthalpy) is significant, it should be noted that the effect is almost completely cancelled by entropy and solvation, and further cancelled by the formation of stable resting states. Thus there is still a long way for this effect to be used in actual catalysis.

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