scholarly journals Benchmarking semiempirical, Hartree–Fock, DFT, and MP2 methods against the ionization energies and electron affinities of short- through long-chain [n]acenes and [n]phenacenes

2016 ◽  
Vol 94 (3) ◽  
pp. 251-258 ◽  
Author(s):  
Sierra Rayne ◽  
Kaya Forest
Keyword(s):  
Density Functional ◽  
Theoretical Data ◽  
Theory Model ◽  
Basis Set ◽  
Electron Affinities ◽  
Ionization Energies ◽  
Hartree Fock ◽  
Wide Range ◽  
High Level ◽  
Long Chain

Vertical and adiabatic ionization energies (IEs) and electron affinities (EAs) were calculated for the n = 1–10 [n]acenes using a wide range of semiempirical, Hartree–Fock, density functional, and second-order Moller–Plesset perturbation theory model chemistries. None of the model chemistries examined was able to accurately predict the IEs or EAs for both short- through long-chain [n]acenes, as well as for extrapolations to the polymeric limit, when compared to available experimental and benchmark theoretical data. Except for 6-31G(d), the choice of the basis set does not affect B3LYP results significantly. Analogous calculations using a suite of eight modern and (or) popular density functionals for the n = 1–10 [n]phenacenes revealed similar problems in estimating the IEs and EAs of these compounds, with the sole exception of the M062X functional for adiabatic IEs and potentially the APFD, B3LYP, and MN12SX functionals for adiabatic EAs. The poor IE/EA prediction performance for the parent [n]acenes and [n]phenacenes may extend to their substituted derivatives and heteroatom-substituted analogs. Consequently, caution should be exercised in the application of non-high-level calculations for estimating the IE/EA of these important classes of materials.

The Electron Affinities of the Alkyldithio Radicals and their Anions

2012 ◽  
Vol 512-515 ◽  
pp. 2059-2063 ◽  
Author(s):  
Hui Yi Pei ◽  
Ai Fang Gao
Keyword(s):  
Electron Affinity ◽  
Density Functional ◽  
Basis Set ◽  
Electron Affinities ◽  
Hartree Fock ◽  
Functional Methods ◽  
Different Types ◽  
Vertical Detachment Energy ◽  
Vertical Electron Affinity ◽  
P Type

The electron affinities of the CnH2n+1SS/CnH2n+1SS- (n=1-5) species have been determined using four different density functional or hybrid Hartree-Fock density functional methods. The basis set used in this work is of double- plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. Three different types of the neutral-anion energy separations reported in this work are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The most reliable adiabatic electron affinities, obtained at the DZP++ BP86 level of theory, are 1.794 eV (for CH3SS), 1.777 eV (for C2H5SS), 1.778 eV (a) and 1.809 eV (b) for the two isomers of C3H7SS, 1.782 eV (a), 1.825 eV (b) and 1.778 eV (c) for the three isomers of C4H9SS, and 1.784 eV (a), 1.875 eV (b), 1.805 eV (c) and 1.835 eV (d) for the three isomers of C5H11SS, respectively.

scholarly journals A Statistically Supported Antioxidant Activity DFT Benchmark—The Effects of Hartree–Fock Exchange and Basis Set Selection on Accuracy and Resources Uptake

Molecules ◽  
2021 ◽  
Vol 26 (16) ◽  
pp. 5058
Author(s):  
Maciej Spiegel ◽  
Andrzej Gamian ◽  
Zbigniew Sroka
Keyword(s):  
Density Functional ◽  
Optimal Level ◽  
Basis Set ◽  
Basis Sets ◽  
Linear Regression Models ◽  
Functional Theory ◽  
Hartree Fock ◽  
Diffuse Function ◽  
Vertical Electron Affinity ◽  
High Level

Polyphenolic compounds are now widely studied using computational chemistry approaches, the most popular of which is Density Functional Theory. To ease this process, it is critical to identify the optimal level of theory in terms of both accuracy and resource usage—a challenge we tackle in this study. Eleven DFT functionals with varied Hartree–Fock exchange values, both global and range-separated hybrids, were combined with 14 differently augmented basis sets to calculate the reactivity indices of caffeic acid, a phenolic acid representative, and compare them to experimental data or a high-level of theory outcome. Aside from the main course, a validation of the widely used Janak’s theorem in the establishment of vertical ionization potential and vertical electron affinity was evaluated. To investigate what influences the values of the properties under consideration, linear regression models were developed and thoroughly discussed. The results were utilized to compute the scores, which let us determine the best and worst combinations and make broad suggestions on the final option. The study demonstrates that M06–2X/6–311G(d,p) is the best fit for such research, and, curiously, it is not necessarily essential to include a diffuse function to produce satisfactory results.

scholarly journals Density Functional Theory and Complete Basis Set Ab Initio Computational Study of Five-, Six-, Seven- and Eight-hydrogen Coordinated Carbon Cations

1999 ◽  
Vol 23 (8) ◽  
pp. 502-503
Author(s):  
Branko S. Jursic
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Computational Study ◽  
Basis Set ◽  
Functional Theory ◽  
Complete Basis ◽  
Complete Basis Set ◽  
High Level

High level ab initio and density functional theory studies are performed on highly protonated methane species.

THE H2NO POTENTIAL ENERGY SURFACE EXPLORED WITH HIGH LEVEL AB INITIO AND DENSITY FUNCTIONAL THEORY METHODS

2007 ◽  
Vol 06 (03) ◽  
pp. 549-562
Author(s):  
ABRAHAM F. JALBOUT
Keyword(s):  
Density Functional Theory ◽  
Potential Energy ◽  
Potential Energy Surface ◽  
Density Functional ◽  
Energy Surface ◽  
Hybrid Methods ◽  
Transition States ◽  
Basis Set ◽  
Functional Theory ◽  
High Level

The transition states for the H 2 NO decomposition and rearrangements mechanisms have been explored by the CBS-Q method or by density functional theory. Six transition states were located on the potential energy surface, which were explored with the Quadratic Complete Basis Set (CBS-Q) and Becke's one-parameter density functional hybrid methods. Interesting deviations between the CBS-Q results and the B1LYP density functional theory lead us to believe that further study into this system is necessary. In the efforts to further assess the stabilities of the transition states, bond order calculations were performed to measure the strength of the bonds in the transition state.

scholarly journals Accuracy and Reliability in the Simulation of Vibrational Spectra: A Comprehensive Benchmark of Energies and Intensities Issuing From Generalized Vibrational Perturbation Theory to Second Order (GVPT2)

2021 ◽  
Vol 8 ◽  
Author(s):  
Qin Yang ◽  
Marco Mendolicchio ◽  
Vincenzo Barone ◽  
Julien Bloino
Keyword(s):  
Perturbation Theory ◽  
Electronic Structure ◽  
Density Functional ◽  
Computational Cost ◽  
Theoretical Data ◽  
Infrared Region ◽  
Second Order ◽  
Basis Set ◽  
Molecular Systems ◽  
The Impact

Vibrational spectroscopy represents an active frontier for the identification and characterization of molecular species in the context of astrochemistry and astrobiology. As new missions will provide more data over broader ranges and at higher resolution, especially in the infrared region, which could be complemented with new spectrometers in the future, support from laboratory experiments and theory is crucial. In particular, computational spectroscopy is playing an increasing role in deepening our understanding of the origin and nature of the observed bands in extreme conditions characterizing the interstellar medium or some planetary atmospheres, not easily reproducible on Earth. In this connection, the best compromise between reliability, feasibility and ease of interpretation is still a matter of concern due to the interplay of several factors in determining the final spectral outcome, with larger molecular systems and non-covalent complexes further exacerbating the dichotomy between accuracy and computational cost. In this context, second-order vibrational perturbation theory (VPT2) together with density functional theory (DFT) has become particularly appealing. The well-known problem of the reliability of exchange-correlation functionals, coupled with the treatment of resonances in VPT2, represents a challenge for the determination of standardized or “black-box” protocols, despite successful examples in the literature. With the aim of getting a clear picture of the achievable accuracy and reliability of DFT-based VPT2 calculations, a multi-step study will be carried out here. Beyond the definition of the functional, the impact of the basis set and the influence of the resonance treatment in VPT2 will be analyzed. For a better understanding of the computational aspects and the results, a short summary of vibrational perturbation theory and the overall treatment of resonances for both energies and intensities will be given. The first part of the benchmark will focus on small molecules, for which very accurate experimental and theoretical data are available, to investigate electronic structure calculation methods. Beyond the reliability of energies, widely used for such systems, the issue of intensities will also be investigated in detail. The best performing electronic structure methods will then be used to treat larger molecular systems, with more complex topologies and resonance patterns.

scholarly journals Optical Properties of Silver-Mediated DNA from Molecular Dynamics and Time Dependent Density Functional Theory

2018 ◽  
Vol 19 (8) ◽  
pp. 2346 ◽  
Author(s):  
Esko Makkonen ◽  
Patrick Rinke ◽  
Olga Lopez-Acevedo ◽  
Xi Chen
Keyword(s):  
Molecular Dynamics ◽  
Density Functional ◽  
Time Dependent ◽  
Basis Set ◽  
Dna Nanostructures ◽  
Exchange Correlation ◽  
Hartree Fock ◽  
Spurious Peak ◽  
20 Nm ◽  
Dependent Density

We report a combined quantum mechanics/molecular mechanics (QM/MM) molecular dynamics and time-dependent density functional (TDDFT) study of metal-mediated deoxyribonucleic acid (M-DNA) nanostructures. For the Ag + -mediated guanine tetramer, we found the maug-cc-pvdz basis set to be sufficient for calculating electronic circular dichroism (ECD) spectra. Our calculations further show that the B3LYP, CAM-B3LYP, B3LYP*, and PBE exchange-correlation functionals are all able to predict negative peaks in the measured ECD spectra within a 20 nm range. However, a spurious positive peak is present in the CAM-B3LYP ECD spectra. We trace the origins of this spurious peak and find that is likely due to the sensitivity of silver atoms to the amount of Hartree–Fock exchange in the exchange-correlation functional. Our presented approach provides guidance for future computational investigations of other Ag + -mediated DNA species.

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