Consequences of Spin Contamination in Unrestricted Calculations on Open-Shell Species: Effect of Hartree−Fock and Møller−Plesset Contributions in Hybrid and Double-Hybrid Density Functional Theory Approaches

Menon, Ambili S.; Radom, Leo

doi:10.1021/jp803064k

Cited by 149 publications

(130 citation statements)

References 52 publications

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“…We had found previously 27 that the double-hybrid UDFT procedure is able to benefit from the inclusion of UHF and UMP2 contributions without incurring to the same extent the problems associated with spin contamination as "normal" unrestricted HF and MP2 often do.…”

Section: Theoretical Methodsmentioning

confidence: 99%

Effect of substituents on the stabilities of multiply-substituted carbon-centered radicals

et al. 2011

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The bond dissociation energies (BDEs) and radical stabilization energies (RSEs) which result from 166 reactions that lead to carbon-centered radicals of the type ∑ CH 2 X, ∑ CHXY and ∑ CXYZ, where X, Y and Z are any of the fourteen substituents H, F, Cl, NH 2 , OH, SH, CH CH 2 , C CH, BH 2 , CHO, COOH, CN, CH 3 , and CF 3 , were calculated using spin-restricted and -unrestricted variants of the double-hybrid B2-PLYP method with the 6-311+G(3df,2p) basis set. The interactions of substituents X, Y, and Z in both the radicals ( ∑ CXYZ) and in the precursor closed-shell molecules (CHXYZ), as well as the extent of additivity of such interactions, were investigated by calculating radical interaction energies (RIEs), molecule interaction energies (MIEs), and deviations from additivity of RSEs (DARSEs) for a set of 152 reactions that lead to di-( ∑ CHXY) and tri-( ∑ CXYZ) substituted carbon-centered radicals. The pairwise quantities describing the effects of pairs of substituents in trisubstituted systems, namely pairwise MIEs (PMIEs), pairwise RIEs (PRIEs) and deviations from pairwise additivity of RSEs (DPARSEs), were also calculated for the set of 61 reactions that lead to trisubstituted radicals ( ∑ CXYZ). Both ROB2-PLYP and UB2-PLYP were found to perform quite well in predicting the quantities related to the stabilities of carbon-centered radicals when compared with available experimental data and with the results obtained from the high-level composite method G3X(MP2)-RAD. Particular selections of substituents or combinations of substituents from the current test set were found to lead to specially stable radicals, increasing the RSEs to a maximum of +68.2 kJ mol -1 for monosubstituted radicals ∑ CH 2 X (X = CH CH 2 ), +131.7 kJ mol -1 for disubstituted radicals ∑ CHXY (X = NH 2 , Y = CHO), and +177.1 kJ mol -1 for trisubstituted radicals ∑ CXYZ (X = NH2, Y = Z = CHO).

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Section: Theoretical Methodsmentioning

confidence: 99%

Effect of substituents on the stabilities of multiply-substituted carbon-centered radicals

et al. 2011

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“…Indeed, unrestricted DFT calculations allow for a study of large open-shell systems with a large degree of confidence. [46] Therefore, the oxidation of the C 51 H 18 and C 79 H 22 nanoparticles by molecular oxygen was studied by first locating the O 2 molecule above the center of the vacant site, at a starting distance of 4.5 from the surface and in an orientation parallel to the surface, and by gradually decreasing the O 2 center of mass, that is, the surface distance along the reaction coordinate, which is defined as the distance between the approaching oxygen molecule center of mass and the carbon atom bearing the s dangling bond around the vacancy. The starting point at 4.5 from the surface was used as a reference for the energy calculations, which were performed by considering only the most stable triplet state.…”

Section: Oxidation Of the Defective Carbonaceous Nanoparticlesmentioning

confidence: 99%

Water Adsorption on Oxidized Single Atomic Vacancies Present at the Surface of Small Carbonaceous Nanoparticles Modeling Soot

et al. 2010

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Quantum calculations are used to study the interaction of water molecules with carbonaceous clusters containing one single carbon atom vacancy. This is a simple but realistic way to model the active surfaces found in soot emitted by aircrafts. Prior to water adsorption, the atomic vacancy is oxidised by an approaching oxygen molecule, which is also likely to occur behind planes. The results of the calculations show that this oxidation process results in the formation of one ketone-like site and one epoxide-like site around the atomic vacancy. These sites may act as nucleation centers for water molecules, which are, however, physisorbed on the oxidized surface, leading to very weak charge transfer with the surface. Although less attractive for water than, for instance, a carboxyl-like site, the ketone-like site can also participate in the hydrophilic behavior of soot primary particles. In contrast, the epoxide-like site formed around the vacancy shows a very low affinity for water molecules.

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“…Based on the calculated values of Ŝ 2 [100], the lowest singlet state (i.e., the ground state) of n-PP exhibits single-reference character (i.e., has no spin contamination and Ŝ 2 = 0.0000), while the lowest triplet state of n-PP possesses some multi-reference character (i.e., Ŝ 2 > 2.0), where the degree of spin contamination increases with the fraction of HartreeFock (HF) exchange adopted in a density functional [99,[104][105][106][107][108]. For ωB97 and ωB97X, the lowest triplet state of long-chain n-PP is slightly spin contaminated, partially degrading the accuracy of ωB97 and ωB97X for E ST .…”

Section: Resultsmentioning

confidence: 99%

Electronic and Optical Properties of the Narrowest Armchair Graphene Nanoribbons Studied by Density Functional Methods

Yeh¹,

Lee²,

Chai³

2016

Aust. J. Chem.

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In the present study, a series of planar poly(p-phenylene) (PPP) oligomers with n phenyl rings (n = 1−20), designated as n-PP, are taken as finite-size models of the narrowest armchair graphene nanoribbons with hydrogen passivation. The singlet-triplet energy gap, vertical ionization potential, vertical electron affinity, fundamental gap, optical gap, and exciton binding energy of n-PP are calculated using Kohn-Sham density functional theory and time-dependent density functional theory with various exchange-correlation density functionals. The ground state of n-PP is shown to be singlet for all the chain lengths studied. In contrast to the lowest singlet state (i.e., the ground state), the lowest triplet state and the ground states of the cation and anion of n-PP are found to exhibit some multi-reference character. Overall, the electronic and optical properties of n-PP obtained from the ωB97 and ωB97X functionals are in excellent agreement with the available experimental data. † These authors contributed equally to this work.

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Consequences of Spin Contamination in Unrestricted Calculations on Open-Shell Species: Effect of Hartree−Fock and Møller−Plesset Contributions in Hybrid and Double-Hybrid Density Functional Theory Approaches

Cited by 149 publications

References 52 publications

Effect of substituents on the stabilities of multiply-substituted carbon-centered radicals

Effect of substituents on the stabilities of multiply-substituted carbon-centered radicals

Water Adsorption on Oxidized Single Atomic Vacancies Present at the Surface of Small Carbonaceous Nanoparticles Modeling Soot

Electronic and Optical Properties of the Narrowest Armchair Graphene Nanoribbons Studied by Density Functional Methods

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