Electronic Properties of Triangle-Shaped Graphene Nanoflakes from TAO-DFT

Deng, Quan; Chai, Jeng-Da

doi:10.1021/acsomega.9b01259

Cited by 18 publications

(33 citation statements)

References 62 publications

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“…For a GS molecule possessing a nonradical nature, the occupation numbers associated with all orbitals are very close to either 0 or 2, yielding a vanishingly small S vN value. Nonetheless, for a GS molecule with a significant radical nature, the active orbital occupation numbers can deviate significantly from 0 and 2 (for example, 0.2-1.8); hence, the corresponding S vN value can greatly increase as the number of active orbitals increases and/or the active orbital occupation numbers are closer to 1 (Rivero et al, 2013;Chai, 2014Chai, , 2017Wu and Chai, 2015;Seenithurai and Chai, 2016, 2017Wu et al, 2016;Yeh et al, 2018;Chung and Chai, 2019;Deng and Chai, 2019;Huang et al, 2020). On the basis of Equation 8, in a spin-restricted TAO-AIMD simulation, the symmetrized von Neumann entropy of a molecule at time t along a TAO-AIMD trajectory can be defined as…”

Section: Symmetrized Von Neumann Entropymentioning

confidence: 99%

“…For n-acene (containing N e electrons), we define the HOMO (i.e., highest occupied molecular orbital) as the (N e /2)th orbital, the LUMO (i.e., lowest unoccupied molecular orbital) as the (N e /2 + 1)th orbital, and so forth (Chai, 2012(Chai, , 2017Wu and Chai, 2015;Wu et al, 2016;Yeh et al, 2018;Chung and Chai, 2019;Deng and Chai, 2019;Seenithurai and Chai, 2019;Huang et al, 2020). For brevity, HOMO and LUMO are denoted as H and L, respectively.…”

Section: Active Orbital Occupation Numbersmentioning

confidence: 99%

“…Owing to its computational efficiency and decent accuracy for exploring the properties of electronic systems at the nanoscale, TAO-DFT has recently been adopted to investigate the electronic properties (Wu and Chai, 2015;Seenithurai and Chai, 2016, 2017, 2020Wu et al, 2016;Yeh and Chai, 2016;Yeh et al, 2018;Chung and Chai, 2019;Deng and Chai, 2019;Huang et al, 2020;Manassir and Pakiari, 2020), hydrogen storage properties (Seenithurai and Chai, 2016, 2017, and vibrational frequencies (Hanson-Heine, 2020) of several electronic systems at the nanoscale, especially for those possessing a radical nature.…”

Section: Introductionmentioning

confidence: 99%

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TAO-DFT-Based Ab Initio Molecular Dynamics

Chai

2020

Front. Chem.

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Recently, AIMD (ab initio molecular dynamics) has been extensively employed to explore the dynamical information of electronic systems. However, it remains extremely challenging to reliably predict the properties of nanosystems with a radical nature using conventional electronic structure methods (e.g., Kohn-Sham density functional theory) due to the presence of static correlation. To address this challenge, we combine the recently formulated TAO-DFT (thermally-assisted-occupation density functional theory) with AIMD. The resulting TAO-AIMD method is employed to investigate the instantaneous/average radical nature and infrared spectra of n-acenes containing n linearly fused benzene rings (n = 2-8) at 300 K. According to the TAO-AIMD simulations, on average, the smaller n-acenes (up to n = 5) possess a nonradical nature, and the larger n-acenes (n = 6-8) possess an increasing radical nature, showing remarkable similarities to the ground-state counterparts at 0 K. Besides, the infrared spectra of n-acenes obtained with the TAO-AIMD simulations are in qualitative agreement with the existing experimental data.

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Section: Symmetrized Von Neumann Entropymentioning

confidence: 99%

Section: Active Orbital Occupation Numbersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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TAO-DFT-Based Ab Initio Molecular Dynamics

Chai

2020

Front. Chem.

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“…In a finite-temperature approach, the fractional orbital occupation numbers are determined by the orbital energies according to some smearing scheme that is typically controlled by a single parameter, an electronic temperature. Because of the simplicity and favorable computational scaling of FT-DFT, it has become a powerful tool for approximate modeling of systems exhibiting strong correlation; such approaches have been used to obtain promising re-sults for a variety of systems [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43].…”

Section: Introductionmentioning

confidence: 99%

Fully numerical calculations on atoms with fractional occupations and range-separated exchange functionals

Lehtola

2020

Phys. Rev. A

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A recently developed finite element approach for fully numerical atomic structure calculations [S. Lehtola, Int. J. Quantum Chem. 119, e25945 (2019)] is extended to the description of atoms with spherically symmetric densities via fractionally occupied orbitals. Specialized versions of Hartree-Fock as well as local density and generalized gradient approximation density functionals are developed, allowing extremely rapid calculations at the basis set limit on the ground and low-lying excited states even for heavy atoms.The implementation of range-separation based on the Yukawa or complementary error function (erfc) kernels is also described, allowing complete basis set benchmarks of modern range-separated hybrid functionals with either integer or fractional occupation numbers. Finally, computation of atomic effective potentials at the local density or generalized gradient approximation levels for the superposition of atomic potentials (SAP) approach [S. Lehtola, J. Chem. Theory Comput. 15, 1593] that has been shown to be a simple and efficient way to initialize electronic structure calculations is described.The present numerical approach is shown to afford beyond microhartree accuracy with a small number of numerical basis functions, and to reproduce literature results for the ground states of atoms and their cations for 1 ≤ Z ≤ 86. Our results indicate that the literature values deviate by up to 10 µE h from the complete basis set limit. The numerical scheme for the erfc kernel is shown to work by comparison to results from large Gaussian basis set calculations from the literature. Spin-restricted ground states are reported for Hartree-Fock and Hartree-Fock-Slater calculations with fractional occupations for 1 ≤ Z ≤ 118.

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“…Besides, aiming to improve the accuracy of TAO-DFT for a wide range of applications, a self-consistent scheme determining the fictitious temperature θ in TAO-DFT has been recently proposed 53 . Since TAO-DFT is a computationally efficient electronic structure method, a number of strongly correlated electron systems at the nanoscale have been studied using TAO-DFT in recent years 16,[54][55][56][57][58][59][60][61][62] . Besides, TAO-DFT has been recently shown to be useful in describing the vibrational spectra of molecules with radical nature 63 .…”

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confidence: 99%

TAO-DFT investigation of electronic properties of linear and cyclic carbon chains

Seenithurai

Chai

2020

Sci Rep

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it has been challenging to adequately investigate the properties of nanosystems with radical nature using conventional electronic structure methods. We address this challenge by calculating the electronic properties of linear carbon chains (l-cc[n]) and cyclic carbon chains (c-cc[n]) with n = 10-100 carbon atoms, using thermally-assisted-occupation density functional theory (TAO-DFT). For all the cases investigated, l-cc[n]/c-cc[n] are ground-state singlets, and c-cc[n] are energetically more stable than l-cc[n]. the electronic properties of l-cc[n]/c-cc[n] reveal certain oscillation patterns for smaller n, followed by monotonic changes for larger n. For the smaller carbon chains, odd-numbered l-cc[n] are more stable than the adjacent even-numbered ones; c-cc[4m + 2]/c-CC[4m] are more/less stable than the adjacent odd-numbered ones, where m are positive integers. As n increases, l-cc[n]/c-cc[n] possess increasing polyradical nature in their ground states, where the active orbitals are delocalized over the entire length of l-cc[n] or the whole circumference of c-cc[n]. Carbon is the most versatile element in forming various structures. In bulk phase, graphite and diamond, which are well-known materials, have been used for centuries. In nanoforms, fullerenes and graphene have been studied in detail for decades. In general, nanostructures can be classified into three categories: zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) nanomaterials. Carbon forms all these nanostructures with unique shapes and properties. Over the past few decades, carbon nanomaterials have been widely studied, and applied in diverse industries 1-3. A number of carbon nanostructures have been synthesized and applied in different fields. The 0D carbon nanomaterials include clusters, quantum dots, nanoflakes, and buckyballs 3. Among them, the C 60 fullerene molecule (containing 12 pentagons and 20 hexagons), where the carbon atoms are sp 2-sp 3-hybridized, has been a popular carbon nanomaterial 1. The discovery of C 60 has led to the flourishment of carbon nanomaterials in various ways. Graphite is a bulk layered material, where the sp 2-hybridized carbon atoms in each layer are arranged in a hexagonal lattice. The 2D carbon nanomaterial, graphene, can be obtained by mechanically exfoliating a single layer of carbon atoms from graphite 2. Thus, graphene, which is a perfect arrangement of hexagons made up of sp 2-hybridized carbon atoms in a 2D planar surface, can be the thinnest (i.e., single-atom-thick) material synthesized ever. Graphene is a zero-gap semiconductor or semimetal with massless Dirac fermions with linear dispersion at low energy. Because of the Dirac-cone feature, graphene has huge potential in electronics applications 2. The discovery of graphene has also led to the discovery of other 2D materials. Besides, if a graphene sheet can be rolled up to form a seamless cylinder, one obtains a carbon nanotube (CNT), which belongs to the class of 1D nanostructures. Note that CNTs were first observed by Iijima in 19...

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Electronic Properties of Triangle-Shaped Graphene Nanoflakes from TAO-DFT

Cited by 18 publications

References 62 publications

TAO-DFT-Based Ab Initio Molecular Dynamics

TAO-DFT-Based Ab Initio Molecular Dynamics

Fully numerical calculations on atoms with fractional occupations and range-separated exchange functionals

TAO-DFT investigation of electronic properties of linear and cyclic carbon chains

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