First Principles Investigation of Binary Chromium Carbides Cr7C3, Cr3C2 and Cr23C6: Electronic Structures, Mechanical Properties and Thermodynamic Properties under Pressure

Binary chromium carbides display excellent wear resistance, extreme stiffness and oxidation resistance under high temperature. The influence of applied pressure on electronic structure, elastic behavior, Debye temperature and hardness of Cr7C3, Cr3C2 and Cr23C6 have been investigated by the density functional theory (DFT) method. The results reveal that lattice parameters and formation enthalpy display an inverse relationship with applied pressure, and Cr3C2 exhibited optimal structural stability. Moreover, Cr-C orbital hybridization tends to be stronger due to the decreased partial density of states (PDOS) of the Cr atom. The difference in electronic distribution of binary carbides has also been investigated, which confirmed that overall orbital hybridization and covalent characteristics has been enhanced. The theoretical hardness was elevated according to the higher bond strength and bond density. In accordance with structural stability data, Cr3C2 has shown maximum theoretical hardness. Furthermore, the anisotropic nature of hardness has been evaluated with external pressure. Cr3C2, and the highest isotropic hardness behavior along with an increase in hardness values with increasing pressure has been observed. In addition, the variation in Debye temperatures of binary chromium carbides under applied pressure has also been predicted. The results provide a theoretical insight into electronic, mechanical and thermodynamic behavior of three binary chromium carbides and show the potential of these novel carbides in a wide range of applications.

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Stability-Ranking of Crystalline Ice Polymorphs Using Density-Functional Theory

Crystals ◽

10.3390/cryst10010040 ◽

2020 ◽

Vol 10 (1) ◽

pp. 40

Author(s):

Pralok K. Samanta ◽

Christian J. Burnham ◽

Niall J. English

Keyword(s):

Density Functional Theory ◽

Structure Prediction ◽

Density Functional ◽

Applied Pressure ◽

External Pressure ◽

Crystal Structure Prediction ◽

Functional Theory ◽

Stability Ranking ◽

High Level ◽

Basin Hopping

In this work, we consider low-enthalpy polymorphs of ice, predicted previously using a modified basin-hopping algorithm for crystal-structure prediction with the TIP4P empirical potential at three pressures (0, 4 and 8 kbar). We compare and (re)-rank the reported ice polymorphs in order of energetic stability, using high-level quantum-chemical calculations, primarily in the guise of sophisticated Density-Functional Theory (DFT) approaches. In the absence of applied pressure, ice Ih is predicted to be energetically more stable than ice Ic, and TIP4P-predicted results and ranking compare well with the results obtained from DFT calculations. However, perhaps not unexpectedly, the deviation between TIP4P- and DFT-calculated results increases with applied external pressure.

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The Flexible Lubrication Performance of Graphene Used in Diamond Interface as a Solid Lubricant: First-Principles Calculations

Nanomaterials ◽

10.3390/nano9121784 ◽

2019 ◽

Vol 9 (12) ◽

pp. 1784

Author(s):

Jianjun Wang ◽

Lin Li ◽

Wentao Yang ◽

Meng Li ◽

Peng Guo ◽

...

Keyword(s):

Diamond Film ◽

First Principles ◽

Density Functional ◽

External Pressure ◽

Diamond Surface ◽

Interfacial Friction ◽

First Principles Calculations ◽

Diamond Surfaces ◽

Lubrication Performance ◽

Wide Range

The interfacial friction performances of graphene covered and hydrogen-terminated diamond surfaces were investigated comparatively by first-principles calculations within density functional theory (DFT). Both systems exhibit similar excellent lubricating effects under small load, but the graphene covered interface presents small friction than that of hydrogenated system for the larger load. The calculated interfacial friction between two sheets of graphene covered diamond surface increases slowly than that of hydrogenated system in a wide range of pressure scale, and the friction difference between the two systems increases with increasing external pressure, indicating that graphene has flexible lubricating properties with high load-carrying capacity. This behavior can be attributed to the large interlayer space and a more uniform interlayer charge distribution of graphene covered diamond interface. Our investigations suggest that graphene is a promising candidate as solid lubricate used in diamond film, and are helpful for the understanding of interfacial friction properties of diamond film.

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Ultra-wide bandgap semiconductor behavior of NaCaF3 fluoro-perovskite with external static isotropic pressure and its impact on optical properties: First-principles computation

10.21203/rs.3.rs-336152/v1 ◽

2021 ◽

Author(s):

Syed Sajid Ali Gillani ◽

Nisar Fatima ◽

M. Shakil ◽

R. Kiran ◽

M. B. Tahir ◽

...

Keyword(s):

Refractive Index ◽

Optical Properties ◽

Band Gap ◽

Density Of States ◽

Density Functional ◽

External Pressure ◽

Partial Density ◽

Total Density ◽

Isotropic Pressure ◽

The Impact

Abstract A comprehensive theoretical study to investigate the outcomes of externally applied static isotropic pressure (0 GPa - 50 GPa) on electronic, optical and structural properties of NaCaF3, using density functional theory (DFT) based CASTEP (Cambridge Serial Total Energy Package) code with ultra-soft pseudo-potential USP plane wave and Perdew Burke Ernzerhof (PBE) exchange-correlation functional of Generalized Gradient Approximation (GGA), is reported. The electronic bandgap shows the increasing trend 4.773 eV - 6.203 eV (direct bandgap) with increasing external pressure. The increase in bandgap is significant up to 20 GPa as compared to higher external pressures. The mystery of increasing band gap is nicely decoded by total density of states (TDOS) and elemental partial density of states (EPDOS). Optical properties have been calculated to analyze the impact of increment in band gap on them. We observed that highest peak of energy loss function L(w) shows the blue shift which confirms the increment of band gap. At zero photon energy, for 0 GPa, the static refractive index n(w) has value of 1.4456. After applying external pressure, there is a slight increase in n(w) which favors the semiconducting behavior of ternary compound. The energy points at which the absorption peak is maxima, the refractive index has lowest value.

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Structural Stability, Elasticity, Thermodynamics and Electronic Structures of L12-Type Ni3X (X=Al, Ti, V, Nb) Phases Under External Pressure Condition

10.21203/rs.3.rs-868726/v1 ◽

2021 ◽

Author(s):

Y H Wu ◽

J S Chen ◽

J Y Ji ◽

Y Z Zhang ◽

Q Z Wang ◽

...

Keyword(s):

Structural Stability ◽

Elastic Constants ◽

First Principles ◽

Electronic Structures ◽

Mechanical Stability ◽

External Pressure ◽

Mechanical Anisotropy ◽

Charge Density Difference ◽

Orbital Hybridization ◽

The Enthalpy Of Formation

Abstract In this paper, the impacts of external pressure on structural stability, elasticity, thermodynamics and relevant electronic structures of L12-type Ni3X (X=Al, Ti, V, Nb) phases were investigated using the first-principles methods. The lattice parameters(a,b,c) and volume(V) of the Ni3X phases decrease with increasing pressure. however, the elastic constants(Cij ), bulk modulus(B), shear modulus(G), and Young's modulus (E) increase. The calculated elastic constants indicate that the mechanical stability and ductility of Ni3X phases enhance with increasing pressure. The mechanical anisotropy of Ni3X phases are enhanced by the raised pressure. Electronic analysis shows that increase pressure makes Ni-d-orbital and X(X=Al, Ti, V, Nb) -d-orbital hybridization stronger and electron transfer increases. The sequence in regard to electron aggregation strength is Ni3Ti>Ni3Nb>Ni3V>Ni3Al. It is more directly reflected in the charge density difference maps. This is consistent with the analysis results of the enthalpy of formation(ΔH) and Debye temperature (ΘD).

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Structural, Electronic, Elastic and Thermal Properties of Li2AgSb: First-Principles Calculations

Zeitschrift für Naturforschung A ◽

10.1515/zna-2015-0127 ◽

2015 ◽

Vol 70 (8) ◽

pp. 611-618

Author(s):

Ji-Hong Li ◽

Xu-Hui Zhu ◽

Yan Cheng ◽

Guang-Fu Ji

Keyword(s):

Thermal Properties ◽

Band Structure ◽

First Principles ◽

Density Functional ◽

Applied Pressure ◽

Density Functional Theory Calculations ◽

Debye Model ◽

Partial Density ◽

Functional Theory ◽

Direct Band

AbstractBased on the first-principles density functional theory calculations combined with the quasi-harmonic Debye model, the pressure dependencies of the structural, elastic, electronic and thermal properties of Li2AgSb were systematically investigated. The calculated lattice parameters and unit cell volume of Li2AgSb at the ground state were in good agreement with the available experimental data. The obtained elastic constants, the bulk modulus and the shear modulus revealed that Li2AgSb is mechanically stable and behaves in a ductile manner under the applied pressure. The elasticity-relevant properties, the Young’s modulus and the Poisson’s ratio showed that pressure can enhance the stiffness of Li2AgSb and that Li2AgSb is mechanically stable up to 20 GPa. The characteristics of the band structure and the partial density of states of Li2AgSb were analysed, showing that Li2AgSb is a semiconductor with a direct band gap of 217 meV at 0 GPa and that the increasing pressure can make the band structure of Li2AgSb become an indirect one. Studies have shown that, unlike temperature, pressure has little effect on the heat capacity and the thermal expansion coefficient of Li2AgSb.

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Intrinsic Stacking Interactions of Natural and Artificial Nucleobases

10.26434/chemrxiv.11400405 ◽

2019 ◽

Author(s):

Drew P. Harding ◽

Laura J. Kingsley ◽

Glen Spraggon ◽

Steven Wheeler

Keyword(s):

Gas Phase ◽

Electrostatic Interactions ◽

Density Functional ◽

Molecular Descriptors ◽

Stacking Interactions ◽

Interaction Energies ◽

Functional Theory ◽

Binding Partner ◽

Heavy Atoms ◽

Wide Range

The intrinsic (gas-phase) stacking energies of natural and artificial nucleobases were explored using density functional theory (DFT) and correlated ab initio methods. Ranking the stacking strength of natural nucleobase dimers revealed a preference in binding partner similar to that seen from experiments, namely G > C > A > T > U. Decomposition of these interaction energies using symmetry-adapted perturbation theory (SAPT) showed that these dispersion dominated interactions are modulated by electrostatics. Artificial nucleobases showed a similar stacking preference for natural nucleobases and were also modulated by electrostatic interactions. A robust predictive multivariate model was developed that quantitively predicts the maximum stacking interaction between natural and a wide range of artificial nucleobases using molecular descriptors based on computed electrostatic potentials (ESPs) and the number of heavy atoms. This model should find utility in designing artificial nucleobase analogs that exhibit stacking interactions comparable to those of natural nucleobases. Further analysis of the descriptors in this model unveil the origin of superior stacking abilities of certain nucleobases, including cytosine and guanine.

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Efficient Prediction of Structural and Electronic Properties of Hybrid 2D Materials Using DFT and Machine Learning

10.26434/chemrxiv.6254756.v1 ◽

2018 ◽

Author(s):

Sherif Tawfik ◽

Olexandr Isayev ◽

Catherine Stampfl ◽

Joseph Shapter ◽

David Winkler ◽

...

Keyword(s):

Machine Learning ◽

Band Gap ◽

Density Functional ◽

2D Materials ◽

Van Der Waals ◽

Building Blocks ◽

Machine Learning Techniques ◽

Interlayer Distance ◽

Computational Screening ◽

Wide Range

Materials constructed from different van der Waals two-dimensional (2D) heterostructures offer a wide range of benefits, but these systems have been little studied because of their experimental and computational complextiy, and because of the very large number of possible combinations of 2D building blocks. The simulation of the interface between two different 2D materials is computationally challenging due to the lattice mismatch problem, which sometimes necessitates the creation of very large simulation cells for performing density-functional theory (DFT) calculations. Here we use a combination of DFT, linear regression and machine learning techniques in order to rapidly determine the interlayer distance between two different 2D heterostructures that are stacked in a bilayer heterostructure, as well as the band gap of the bilayer. Our work provides an excellent proof of concept by quickly and accurately predicting a structural property (the interlayer distance) and an electronic property (the band gap) for a large number of hybrid 2D materials. This work paves the way for rapid computational screening of the vast parameter space of van der Waals heterostructures to identify new hybrid materials with useful and interesting properties.

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Ab initio calculation on the Optical Properties of AA- Stacked two dimensional Graphene, Silicene, Germanene, and Stanene

International Journal of Computational Physics Series ◽

10.29167/a1i1p46-50 ◽

2018 ◽

Vol 1 (1) ◽

pp. 46-50

Author(s):

Rita John ◽

Benita Merlin

Keyword(s):

Optical Properties ◽

Band Structure ◽

Density Functional ◽

Electronic Band Structure ◽

Complex Refractive Index ◽

Single Layer ◽

Generalized Gradient ◽

Electronic Band ◽

Wide Range ◽

Optical Region

In this study, we have analyzed the electronic band structure and optical properties of AA-stacked bilayer graphene and its 2D analogues and compared the results with single layers. The calculations have been done using Density Functional Theory with Generalized Gradient Approximation as exchange correlation potential as in CASTEP. The study on electronic band structure shows the splitting of valence and conduction bands. A band gap of 0.342eV in graphene and an infinitesimally small gap in other 2D materials are generated. Similar to a single layer, AA-stacked bilayer materials also exhibit excellent optical properties throughout the optical region from infrared to ultraviolet. Optical properties are studied along both parallel (||) and perpendicular ( ) polarization directions. The complex dielectric function (ε) and the complex refractive index (N) are calculated. The calculated values of ε and N enable us to analyze optical absorption, reflectivity, conductivity, and the electron loss function. Inferences from the study of optical properties are presented. In general the optical properties are found to be enhanced compared to its corresponding single layer. The further study brings out greater inferences towards their direct application in the optical industry through a wide range of the optical spectrum.

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