scholarly journals Investigating ultrafast two-pulse experiments on single DNQDI fluorophores: a stochastic quantum approach

2020 ◽  
Vol 22 (29) ◽  
pp. 16734-16746
Author(s):  
Giulia Dall'Osto ◽  
Emanuele Coccia ◽  
Ciro A. Guido ◽  
Stefano Corni
Keyword(s):  
Wave Function ◽  
Electronic Structure ◽  
Dft Methods ◽  
Quantum Approach ◽  
Time Propagation ◽  
Function Time

The vibrational and electronic structure of the fluorophore calculated with DFT methods coupled with wave function time propagation by SSE.

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>

scholarly journals Quantum algorithms for electronic structure calculations: Particle-hole Hamiltonian and optimized wave-function expansions

2018 ◽  
Vol 98 (2) ◽  
Author(s):  
Panagiotis Kl. Barkoutsos ◽  
Jerome F. Gonthier ◽  
Igor Sokolov ◽  
Nikolaj Moll ◽  
Gian Salis ◽  
...  
Keyword(s):  
Wave Function ◽  
Electronic Structure ◽  
Quantum Algorithms ◽  
Electronic Structure Calculations ◽  
Structure Calculations

Density Functional Approaches to Relativistic Quantum Mechanics

2007 ◽  
Author(s):  
Kenneth G. Dyall ◽  
Knut Faegri
Keyword(s):  
Wave Function ◽  
Quantum Mechanics ◽  
Electron Density ◽  
Density Functional ◽  
Relativistic Quantum ◽  
Electron System ◽  
State Density ◽  
Dft Methods ◽  
Particle Wave Function ◽  
Spatial Coordinates

The wave function is an elusive and somewhat mysterious object. Nobody has ever observed the wave function directly: rather, its existence is inferred from the various experiments whose outcome is most rationally explained using a wave function interpretation of quantum mechanics. Further, the N-particle wave function is a rather complicated construction, depending on 3N spatial coordinates as well as N spin coordinates, correlated in a manner that almost defies description. By contrast, the electron density of an N-electron system is a much simpler quantity, described by three spatial coordinates and even accessible to experiment. In terms of the wave function, the electron density is expressed as . . . ρ(r) = N ∫ Ψ* (r1,r2,...,rN)Ψ (r1,r2,...,rN)dr2dr3 ...drN (14.1) . . . where the sum over spin coordinates is implicit. It might be much more convenient to have a theory based on the electron density rather than the wave function. The description would be much simpler, and with a greatly reduced (and constant) number of variables, the calculation of the electron density would hopefully be faster and less demanding. We also note that given the correct ground state density, we should be able to calculate any observable quantity of a stationary system. The answer to these hopes is density functional theory, or DFT. Over the past decade, DFT has become one of the most widely used tools of the computational chemist, and in particular for systems of some size. This success has come despite complaints about arbitrary parametrization of potentials, and laments about the absence of a universal principle (other than comparison with experiment) that can guide improvements in the way the variational principle has led the development of wave-function-based methods. We do not intend to pursue that particular discussion, but we note as a historical fact that many important early contributions to relativistic quantum chemistry were made using DFT-like methods. Furthermore, there is every reason to try to extend the success of nonrelativistic DFT methods to the relativistic domain. We suspect that their potential for conquering a sizable part of this field is at least as large as it has been in the nonrelativistic domain.

Mechanisms of photoreactivity in hydrogen-bonded adenine–H2O complexes

2019 ◽  
Vol 21 (26) ◽  
pp. 14238-14249 ◽  
Author(s):  
Xiuxiu Wu ◽  
Johannes Ehrmaier ◽  
Andrzej L. Sobolewski ◽  
Tolga N. V. Karsili ◽  
Wolfgang Domcke
Keyword(s):  
Wave Function ◽  
Electronic Structure ◽  
Ab Initio ◽  
Electronic Structure Calculations ◽  
Water Molecules ◽  
Photoinduced Reactions ◽  
Structure Calculations ◽  
Hydrogen Bonded

The mechanisms of photoinduced reactions of adenine with water molecules in hydrogen-bonded adenine–water complexes were investigated with ab initio wave-function-based electronic-structure calculations.

scholarly journals Electronic Structure, Spectroscopic (IR, Raman, UV-Vis, NMR), Optoelectronic, and NLO Properties Investigations of Rubescin E (C31H36O7) Molecule in Gas Phase and Chloroform Solution Using Ab Initio and DFT Methods

2019 ◽  
Vol 2019 ◽  
pp. 1-22 ◽  
Author(s):  
Richard Arnaud Yossa Kamsi ◽  
Geh Wilson Ejuh ◽  
Fidèle Tchoffo ◽  
Pierre Mkounga ◽  
Jean-Marie Bienvenu Ndjaka
Keyword(s):  
Electronic Structure ◽  
Chloroform Solution ◽  
3D Analysis ◽  
Coupling Constant ◽  
Dft Methods ◽  
Reactivity Descriptors ◽  
H Nmr ◽  
Quantum Chemical Methods ◽  
Td Dft ◽  
Electric Susceptibility

Quantum chemical methods were used to study the electronic structure and some physicochemical properties of Rubescin E molecule. Good agreement with experiment was found for J3H-H coupling constant, IR, 1H NMR, and 13C NMR. The excitation energy and oscillator strength calculated by TD-DFT also complement with experiment. Large values were obtained for dipole moment, polarizability, first static hyperpolarizability, electric susceptibility, refractive index, and dielectric constant, meaning that Rubescin E has strong optical and phonon application and can be a good candidate as NLOs material. The 3D analysis of the title molecule leads us to the conclusion that electron can easily be transferred from furan to tetrahydrofuran ring. The global reactivity descriptors were evaluated. Mulliken, ESP, and NBO charges comparisons were carried out and described.

scholarly journals Electronic Structure Benchmark Calculations of CO2 Fixing Elementary Chemical Steps in RuBisCO Using the Projector-Based Embedding Approach

2020 ◽  
Author(s):  
Oscar A. Douglas-Gallardo ◽  
Ian J. Shepherd ◽  
Simon Bennie ◽  
Kara Ranaghan ◽  
Adrian Mulholland ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Ab Initio ◽  
Atmospheric Carbon Dioxide ◽  
Density Functional ◽  
Enzyme Reaction ◽  
Dft Methods ◽  
Carboxylase Activity ◽  
Bisphosphate Carboxylase ◽  
Carbon Carbon Bond ◽  
Reaction Energies

<div>Ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) is the main enzyme involved in atmospheric carbon dioxide (CO<sub>2</sub>) fixation in the biosphere. This enzyme catalyses a set of five chemical steps that take place in the same active-site within magnesium (II) coordination sphere. Here, a set of electronic structure benchmark calculations have been carried out on a reaction path proposed by Gready <i>et al.</i> by means of the projector-based embedding approach. Activation and reaction energies for all main steps catalyzed by RuBisCO have been calculated at the MP2, SCS-MP2, CCSD and CCSD(T)/aug-cc-pVDZ and cc-pVDZ levels of theory. </div><div><br></div><div>The treatment of the magnesium cation with post-HF methods is explored to determine the nature of its involvement in the mechanism. With the high-level ab initio values as a reference, we tested the performance of a set of density functional theory (DFT) exchange-correlation (xc) functionals in reproducing the reaction energetics of RuBisCO carboxylase activity on a set of model fragments. Different DFT xc-functionals show large variation in activation and reaction energies. Activation and reaction energies computed at the B3LYP level are close to the reference SCS-MP2 results for carboxylation, hydration and protonation reactions.</div><div><br></div><div>However, for the carbon-carbon bond dissociation reaction, B3LYP and other functionals give results that differ significantly from the ab initio reference values. The results show the applicability of the projector-based embedding approach to metalloenzymes. This technique removes the uncertainty associated with the selection of different DFT xc-functionals and so can overcome some of inherent limitations of DFT calculations, complementing and potentially adding to modelling of enzyme reaction mechanisms with DFT methods.</div>

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