scholarly journals Electronic Properties of Carbon Nanobelts Predicted by Thermally-Assisted-Occupation DFT

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2224
Author(s):  
Sonai Seenithurai ◽  
Jeng-Da Chai
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Large Scale ◽  
Von Neumann Entropy ◽  
Electronic Systems ◽  
Functional Theory ◽  
Von Neumann ◽  
Hartree Fock ◽  
Prediction Of Properties ◽  
Occupation Numbers

Accurate prediction of properties of large-scale multi-reference (MR) electronic systems remains difficult for traditional computational methods (e.g., the Hartree–Fock theory and Kohn–Sham density functional theory (DFT)). Recently, thermally-assisted-occupation (TAO)-DFT has been demonstrated to offer reliable description of electronic properties of various large-scale MR electronic systems. Consequently, in this work, TAO-DFT is used to unlock the electronic properties associated with C-Belt[n] (i.e., the carbon nanobelts containing n fused 12-membered carbon rings). Our calculations show that for all the system sizes reported (n = 4–24), C-Belt[n] have singlet ground states. In general, the larger the size of C-Belt[n], the more pronounced the MR character of ground-state C-Belt[n], as evident from the symmetrized von Neumann entropy and the occupation numbers of active TAO-orbitals. Furthermore, the active TAO-orbitals are delocalized along the circumference of C-Belt[n], as evident from the visualization of active TAO-orbitals.

scholarly journals TAO-DFT Study on the Electronic Properties of Diamond-Shaped Graphene Nanoflakes

Nanomaterials ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 1236 ◽  
Author(s):  
Hong-Jui Huang ◽  
Sonai Seenithurai ◽  
Jeng-Da Chai
Keyword(s):  
Electronic Properties ◽  
Density Functional ◽  
Energy Gap ◽  
Quantitative Measure ◽  
Smooth Transition ◽  
Von Neumann Entropy ◽  
Triplet Energy ◽  
Von Neumann ◽  
Graphene Nanoflakes ◽  
Radical Nature

At the nanoscale, it has been rather troublesome to properly explore the properties associated with electronic systems exhibiting a radical nature using traditional electronic structure methods. Graphene nanoflakes, which are graphene nanostructures of different shapes and sizes, are typical examples. Recently, TAO-DFT (i.e., thermally-assisted-occupation density functional theory) has been formulated to tackle such challenging problems. As a result, we adopt TAO-DFT to explore the electronic properties associated with diamond-shaped graphene nanoflakes with n = 2–15 benzenoid rings fused together at each side, designated as n-pyrenes (as they could be expanded from pyrene). For all the n values considered, n-pyrenes are ground-state singlets. With increasing the size of n-pyrene, the singlet-triplet energy gap, vertical ionization potential, and fundamental gap monotonically decrease, while the vertical electron affinity and symmetrized von Neumann entropy (which is a quantitative measure of radical nature) monotonically increase. When n increases, there is a smooth transition from the nonradical character of the smaller n-pyrenes to the increasing polyradical nature of the larger n-pyrenes. Furthermore, the latter is shown to be related to the increasing concentration of active orbitals on the zigzag edges of the larger n-pyrenes.

scholarly journals Computational Study of some Double Headed Acyclo-C-Nucleosides

2015 ◽  
Vol 61 ◽  
pp. 1-11
Author(s):  
Sarah Amara ◽  
Noureddine Tchouar ◽  
Salah Belaidi
Keyword(s):  
Electronic Properties ◽  
Ground State ◽  
Density Functional ◽  
Computational Study ◽  
Experimental Studies ◽  
Functional Theory ◽  
Hartree Fock ◽  
Structural And Electronic Properties ◽  
Semi Empirical

In the present paper we have a focus in a study of theoretical characterization of three double headed acyclo-C-nucleosides, which are a recent target of experimental studies. The structural and electronic properties of double headed acyclo-C-nucleosides, 1,4-bis (3-mercapto-1H-1,2,4-triazol-5-yl) butane-1,2,3,4-tetrol, 1,4-bis (4-amino-5-mercapto-4H-1,2,4-triazol-3-yl) butane-1,2,3,4-tetrol and 5,5'-(1,2,3,4-tetrahydroxybutane-1,4-diyl) bis (1,3,4-oxadiazole-2(3H)-thione), have been investigated theoretically by performing semi-empirical molecular orbital, ab initio Hartree-Fock (HF) and Density Functional Theory (DFT) calculations. Geometries of the three molecules are optimized at the level of Austin Model 1 (AM1). The electronic properties and relative energies of the molecules have been calculated by HF and DFT in the ground state.

scholarly journals Harnessing the Power of Multi-GPU Acceleration into the Quantum Interaction Computational Kernel Program

2021 ◽  
Author(s):  
Madushanka Manathunga ◽  
Chi Jin ◽  
Vinicius Cruzeiro ◽  
Yipu Miao ◽  
Dawei Mu ◽  
...  
Keyword(s):  
Load Balancing ◽  
Ab Initio ◽  
Density Functional ◽  
Large Scale ◽  
Functional Theory ◽  
Multiple Gpus ◽  
Hartree Fock ◽  
Large Size ◽  
Electron Repulsion Integrals ◽  
Computational Kernel

<div><div><div><p>We report a new multi-GPU capable ab initio Hartree-Fock/density functional theory implementation integrated into the open source QUantum Interaction Computational Kernel (QUICK) program. Details on the load balancing algorithms for electron repulsion integrals and exchange correlation quadrature across multiple GPUs are described. Benchmarking studies carried out on up to 4 GPU nodes, each containing 4 NVIDIA V100-SMX2 type GPUs demonstrate that our implementation is capable of achiev- ing excellent load balancing and high parallel efficiency. For representative medium to large size protein/organic molecular sys- tems, the observed efficiencies remained above 86%. The accelerations on NVIDIA A100, P100 and K80 platforms also have real- ized parallel efficiencies higher than 74%, paving the way for large-scale ab initio electronic structure calculations.</p></div></div></div>

scholarly journals Harnessing the Power of Multi-GPU Acceleration into the Quantum Interaction Computational Kernel Program

2021 ◽  
Author(s):  
Madushanka Manathunga ◽  
Chi Jin ◽  
Vinicius Cruzeiro ◽  
Yipu Miao ◽  
Dawei Mu ◽  
...  
Keyword(s):  
Load Balancing ◽  
Ab Initio ◽  
Density Functional ◽  
Large Scale ◽  
Functional Theory ◽  
Multiple Gpus ◽  
Hartree Fock ◽  
Large Size ◽  
Electron Repulsion Integrals ◽  
Computational Kernel

<div><div><div><p>We report a new multi-GPU capable ab initio Hartree-Fock/density functional theory implementation integrated into the open source QUantum Interaction Computational Kernel (QUICK) program. Details on the load balancing algorithms for electron repulsion integrals and exchange correlation quadrature across multiple GPUs are described. Benchmarking studies carried out on up to 4 GPU nodes, each containing 4 NVIDIA V100-SMX2 type GPUs demonstrate that our implementation is capable of achiev- ing excellent load balancing and high parallel efficiency. For representative medium to large size protein/organic molecular sys- tems, the observed efficiencies remained above 86%. The accelerations on NVIDIA A100, P100 and K80 platforms also have real- ized parallel efficiencies higher than 74%, paving the way for large-scale ab initio electronic structure calculations.</p></div></div></div>

Benchmark of Simplified Time-Dependent Density Functional Theory for UV-Vis Spectral Properties of Porphyrinoids

2019 ◽  
Author(s):  
Kamal Batra ◽  
Stefan Zahn ◽  
Thomas Heine
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Large Scale ◽  
Absolute Error ◽  
Time Dependent ◽  
Basis Set ◽  
Basis Sets ◽  
Functional Theory ◽  
Framework Materials ◽  
Dependent Density

<p>We thoroughly benchmark time-dependent density- functional theory for the predictive calculation of UV/Vis spectra of porphyrin derivatives. With the aim to provide an approach that is computationally feasible for large-scale applications such as biological systems or molecular framework materials, albeit performing with high accuracy for the Q-bands, we compare the results given by various computational protocols, including basis sets, density-functionals (including gradient corrected local functionals, hybrids, double hybrids and range-separated functionals), and various variants of time-dependent density-functional theory, including the simplified Tamm-Dancoff approximation. An excellent choice for these calculations is the range-separated functional CAM-B3LYP in combination with the simplified Tamm-Dancoff approximation and a basis set of double-ζ quality def2-SVP (mean absolute error [MAE] of ~0.05 eV). This is not surpassed by more expensive approaches, not even by double hybrid functionals, and solely systematic excitation energy scaling slightly improves the results (MAE ~0.04 eV). </p>

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