scholarly journals RPA natural orbitals and their application to post-Hartree-Fock electronic structure methods

2019 ◽  
Vol 151 (21) ◽  
pp. 214106 ◽  
Author(s):  
Benjamin Ramberger ◽  
Zoran Sukurma ◽  
Tobias Schäfer ◽  
Georg Kresse
Keyword(s):  
Electronic Structure ◽  
Natural Orbitals ◽  
Hartree Fock ◽  
Electronic Structure Methods

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>

scholarly journals Exploring the Franck-Condon region of a photoexcited charge transfer complex in solution to interpret femtosecond stimulated Raman spectroscopy: excited state electronic structure methods to unveil non-radiative pathways

2021 ◽  
Author(s):  
Federico Coppola ◽  
Paola Cimino ◽  
Umberto Raucci ◽  
Maria Gabriella Chiariello ◽  
Alessio Petrone ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Electronic Structure ◽  
Excited State ◽  
Charge Transfer ◽  
Charge Transfer Complex ◽  
Main Role ◽  
Photoinduced Charge Transfer ◽  
Electronic Structure Methods ◽  
Franck Condon ◽  
Photoinduced Charge

We present electronic structure methods to unveil non-radiative pathways of photoinduced charge transfer (CT) reactions that play a main role in photophysics and light harvesting technologies. A prototypical π-stacked molecular...

Ab Initio Study of Electronic Structure of RDX Molecular Crystal

1992 ◽  
Vol 296 ◽  
Author(s):  
Guang Gao ◽  
Ravindra Pandey ◽  
A. Barry Kunz
Keyword(s):  
Electronic Structure ◽  
Hot Spots ◽  
Molecular Crystal ◽  
Perfect Crystal ◽  
Local Region ◽  
Molecular Cluster ◽  
Ab Initio Study ◽  
Hartree Fock ◽  
Cyclotrimethylene Trinitramine ◽  
Defective Crystal

AbstractAn embedded molecular cluster model is used to study the electronic structure of cyclotrimethylene trinitramine(RDX) molecular crystal. In this model, a molecular cluster describing a local region of the crystal is treated in the Hartree-Fock approximation. The embedding lattice is represented by multipoles that are determined quantum-mechanically. Cluster-lattice orthogonality is achieved by transforming canonical orbitals to orbitals which are localized on individual molecular sites by means of a self-consistent localization potential. Results for the free molecule and the perfect crystal demonstrate the domination of three N-NO2 groups on intermolecular properties. For the defective crystal, results show a significant distortion in the electronic structure caused by local deformations in the lattice that may account for the formation of hot spots.

Nonadiabatic dynamics simulation of keto isocytosine: a comparison of dynamical performance of different electronic-structure methods

2017 ◽  
Vol 19 (29) ◽  
pp. 19168-19177 ◽  
Author(s):  
Deping Hu ◽  
Yan Fang Liu ◽  
Andrzej L. Sobolewski ◽  
Zhenggang Lan
Keyword(s):  
Electronic Structure ◽  
Dynamics Simulation ◽  
Nonadiabatic Dynamics ◽  
Electronic Structure Methods ◽  
Reaction Channels ◽  
Dynamics Simulations

Different reaction channels are obtained in the nonadiabatic dynamics simulations of isocytosine at CASSCF and ADC(2) levels.

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