scholarly journals Measuring Shared Electrons in Extended Molecular Systems: Covalent Bonds from Plane-Wave Representation of Wave Function

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 4044
Author(s):  
Giovanni La Penna ◽  
Davide Tiana ◽  
Paolo Giannozzi
Keyword(s):  
Wave Function ◽  
Bond Order ◽  
High Performance ◽  
Density Functional ◽  
Large Scale ◽  
Covalent Bonds ◽  
Molecular Systems ◽  
Chemical Concepts ◽  
Atomistic Calculations ◽  
Quantum Espresso

In the study of materials and macromolecules by first-principle methods, the bond order is a useful tool to represent molecules, bulk materials and interfaces in terms of simple chemical concepts. Despite the availability of several methods to compute the bond order, most applications have been limited to small systems because a high spatial resolution of the wave function and an all-electron representation of the electron density are typically required. Both limitations are critical for large-scale atomistic calculations, even within approximate density-functional theory (DFT) approaches. In this work, we describe our methodology to quickly compute delocalization indices for all atomic pairs, while keeping the same representation of the wave function used in most compute-intensive DFT calculations on high-performance computing equipment. We describe our implementation into a post-processing tool, designed to work with Quantum ESPRESSO, a popular open-source DFT package. In this way, we recover a description in terms of covalent bonds from a representation of wave function containing no explicit information about atomic types and positions.

Comparative Study of Defect Properties in GaN: Ab Initio and Empirical Potential Calculations

2003 ◽  
Vol 792 ◽  
Author(s):  
Fei Gao ◽  
Eric J. Bylaska ◽  
Anter El-Azab ◽  
William J. Weber
Keyword(s):  
Density Functional ◽  
Large Scale ◽  
Bond Distance ◽  
Antisite Defect ◽  
Covalent Bonds ◽  
Atomic Wires ◽  
Empirical Potentials ◽  
Favorable Configuration ◽  
Antisite Defects ◽  
Large Scale Simulations

ABSTRACTDensity functional theory (DFT) is used to study the formation, properties and atomic configurations of monovacancies, antisite defects and possible interstitials in GaN. The relaxation around a vacancy is generally small, but the relaxation around antisite defects is large, particularly for a Ga antisite defect, which is not stable and converts to an N-N<0001> split interstitial. All N interstitials, starting from any possible site, eventually transfer into the N-N split interstitials, forming N2 molecules with one N-N bond, but also some covalent bonds to the surrounding atoms. In the case of Ga interstitials, the most favorable configuration is the Ga octahedral interstitial. However, it is found that the Ga-Ga<1120> split interstitial can bridge the gap between non-bonded Ga atoms along the <1120> direction, which leads to the formation of Ga atomic wires in GaN, with bond distance (2.3Å) close to those noted in bulk Ga. In addition, two representative potentials, namely Stillinger-Weber and Tersoff-Brenner potentials, have been employed to determine the formation of defects using molecular dynamics (MD) method in GaN. The MD results are discussed and compared to DFT calculations. The present DFT and MD results provide guidelines for evaluating the quality and fit of empirical potentials for large-scale simulations of ion-solid interaction and thermal annealing of defects in GaN.

scholarly journals Formulation and Implementation of Density Functional Embedding Theory using Products of Basis Functions

2020 ◽  
Author(s):  
Vladimir Rybkin
Keyword(s):  
Condensed Phase ◽  
Density Functional ◽  
Large Scale ◽  
Plane Waves ◽  
Basis Functions ◽  
Basis Set ◽  
Transfer Reactions ◽  
Molecular Systems ◽  
Embedding Theory ◽  
Proton Transfer Reactions

The representation of embedding potential in using products of AO basis functions has been developed in the context of density functional embedding theory (DFET). The formalism allows to treat pseudopotential and all-electron calculations on the same footing and enables simple transfer of the embedding potential in the compact matrix form. In addition, a simple cost-reduction procedure for basis set and potential reduction has been proposed. The theory has been implemented for the condensed-phase and molecular systems using Gaussian and Plane Waves (GPW) and Gaussian and Augmented Plane Waves (GAPW) formalisms and tested for proton transfer reactions in the cluster and the condensed phase. The computational scaling of the embedding potential optimization is similar to this of hybrid DFT with a significantly reduced prefactor and allows for large-scale applications.<div><br></div>

scholarly journals Formulation and Implementation of Density Functional Embedding Theory using Products of Basis Functions

2020 ◽  
Author(s):  
Vladimir Rybkin
Keyword(s):  
Condensed Phase ◽  
Density Functional ◽  
Large Scale ◽  
Plane Waves ◽  
Basis Functions ◽  
Basis Set ◽  
Transfer Reactions ◽  
Molecular Systems ◽  
Embedding Theory ◽  
Proton Transfer Reactions

The representation of embedding potential in using products of AO basis functions has been developed in the context of density functional embedding theory (DFET). The formalism allows to treat pseudopotential and all-electron calculations on the same footing and enables simple transfer of the embedding potential in the compact matrix form. In addition, a simple cost-reduction procedure for basis set and potential reduction has been proposed. The theory has been implemented for the condensed-phase and molecular systems using Gaussian and Plane Waves (GPW) and Gaussian and Augmented Plane Waves (GAPW) formalisms and tested for proton transfer reactions in the cluster and the condensed phase. The computational scaling of the embedding potential optimization is similar to this of hybrid DFT with a significantly reduced prefactor and allows for large-scale applications.<div><br></div>

Large-Scale Electronic-Structure Calculations in the Real-Space Scheme: Bilayer Graphene and Silicene

2013 ◽  
Vol 1595 ◽  
Author(s):  
Kazuyuki Uchida ◽  
Zhixin Guo ◽  
Jun-ichi Iwata ◽  
Atsushi Oshiyama
Keyword(s):  
High Performance ◽  
Density Functional ◽  
Large Scale ◽  
Density Functional Theory Calculation ◽  
Bilayer Graphene ◽  
Real Space ◽  
Functional Theory ◽  
Parallel Supercomputers ◽  
Ag Substrate ◽  
Theory Calculation

ABSTRACTWe have developed our original DFT (density-functional theory) calculation code “RSDFT” using real-space schemes. The code is FFT-free, leading to high-performance computing in massively-parallel supercomputers. The code allows us to deal with systems including huge numbers of atoms from first-principles. We have applied our schemes to clarify atomic and electronic structures of two relevant nano-scale systems: twisted bilayer graphene and silicene on Ag substrate.

scholarly journals Interface Engineering of CoS/CoO@N-Doped Graphene Nanocomposite for High-Performance Rechargeable Zn–Air Batteries

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Yuhui Tian ◽  
Li Xu ◽  
Meng Li ◽  
Ding Yuan ◽  
Xianhu Liu ◽  
...  
Keyword(s):  
High Performance ◽  
Density Functional ◽  
Large Scale ◽  
Electronic Conductivity ◽  
Specific Capacity ◽  
Density Functional Theory Calculations ◽  
Interfacial Structure ◽  
Catalyst Stability ◽  
Bifunctional Electrocatalyst ◽  
Doped Graphene

Abstract Low cost and green fabrication of high-performance electrocatalysts with earth-abundant resources for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for the large-scale application of rechargeable Zn–air batteries (ZABs). In this work, our density functional theory calculations on the electrocatalyst suggest that the rational construction of interfacial structure can induce local charge redistribution, improve the electronic conductivity and enhance the catalyst stability. In order to realize such a structure, we spatially immobilize heterogeneous CoS/CoO nanocrystals onto N-doped graphene to synthesize a bifunctional electrocatalyst (CoS/CoO@NGNs). The optimization of the composition, interfacial structure and conductivity of the electrocatalyst is conducted to achieve bifunctional catalytic activity and deliver outstanding efficiency and stability for both ORR and OER. The aqueous ZAB with the as-prepared CoS/CoO@NGNs cathode displays a high maximum power density of 137.8 mW cm−2, a specific capacity of 723.9 mAh g−1 and excellent cycling stability (continuous operating for 100 h) with a high round-trip efficiency. In addition, the assembled quasi-solid-state ZAB also exhibits outstanding mechanical flexibility besides high battery performances, showing great potential for applications in flexible and wearable electronic devices.

scholarly journals Enhanced Potassium-Ion Storage of the 3D Carbon Superstructure by Manipulating the Nitrogen-Doped Species and Morphology

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Yanhua Li ◽  
Kui Xiao ◽  
Cong Huang ◽  
Jin Wang ◽  
Ming Gao ◽  
...  
Keyword(s):  
Energy Storage ◽  
High Performance ◽  
Density Functional ◽  
Large Scale ◽  
Specific Capacity ◽  
Rate Capability ◽  
High Energy ◽  
Potassium Ion ◽  
High Energy Density ◽  
Superior Performance

Abstract Potassium-ion batteries (PIBs) are attractive for grid-scale energy storage due to the abundant potassium resource and high energy density. The key to achieving high-performance and large-scale energy storage technology lies in seeking eco-efficient synthetic processes to the design of suitable anode materials. Herein, a spherical sponge-like carbon superstructure (NCS) assembled by 2D nanosheets is rationally and efficiently designed for K+ storage. The optimized NCS electrode exhibits an outstanding rate capability, high reversible specific capacity (250 mAh g−1 at 200 mA g−1 after 300 cycles), and promising cycling performance (205 mAh g−1 at 1000 mA g−1 after 2000 cycles). The superior performance can be attributed to the unique robust spherical structure and 3D electrical transfer network together with nitrogen-rich nanosheets. Moreover, the regulation of the nitrogen doping types and morphology of NCS-5 is also discussed in detail based on the experiments results and density functional theory calculations. This strategy for manipulating the structure and properties of 3D materials is expected to meet the grand challenges for advanced carbon materials as high-performance PIB anodes in practical applications.

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