Theoretical Investigations on Mechanical Stability and Electronic Structure of NbN under Pressures

2011 ◽  
Vol 90-93 ◽  
pp. 1264-1271
Author(s):  
Xiao Feng Li ◽  
Jun Yi Du
Keyword(s):  
Debye Temperature ◽  
Density Functional ◽  
Mechanical Stability ◽  
Structural Parameters ◽  
Theoretical Data ◽  
Hexagonal Structure ◽  
Functional Theory ◽  
Theoretical Investigations ◽  
Crystallographic Structures ◽  
Good Agreement

The ground structure, elastic and electronic properties of several phases of NbN are determined based on ab initio total-energy calculations within the framework of density functional theory. Among the five crystallographic structures that have been investigated, the hexagonal phases have been found to be more stable than the cubic ones. The calculated equilibrium structural parameters are in good agreement with the available experimental results. The elastic constants of five structures in NbN are calculated, which are in consistent with the obtained theoretical and experimental data. The corresponding Debye temperature and elastic ansitropies are also obtained. The Debye temperature of NbN in various structures consistent with available experimental and theoretical data, in which the Debye temperature of δ-NbN is highest. The anisotropies of ZB-NbN, NaCl-NbN, CsCl-NbN gradually increases. For hexagonal structure, the anisotropies of ε-NbN are stronger than that of δ-NbN. The electronic structures of NbN under pressure are investigated. It is found that NbN have metallization and the hybridizations of atoms in NbN under pressure become stronger.

scholarly journals Pressure Effect on Elastic Constants and Related Properties of Ti3Al Intermetallic Compound: A First-Principles Study

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2015 ◽  
Author(s):  
Xianshi Zeng ◽  
Rufang Peng ◽  
Yanlin Yu ◽  
Zuofu Hu ◽  
Yufeng Wen ◽  
...  
Keyword(s):  
Intermetallic Compound ◽  
Debye Temperature ◽  
Elastic Constants ◽  
First Principles ◽  
Density Functional ◽  
Mechanical Stability ◽  
Theoretical Data ◽  
Young’S Moduli ◽  
Anisotropic Factor ◽  
Isotropic Pressure

Using first-principles calculations based on density functional theory, the elastic constants and some of the related physical quantities, such as the bulk, shear, and Young’s moduli, Poisson’s ratio, anisotropic factor, acoustic velocity, minimum thermal conductivity, and Debye temperature, are reported in this paper for the hexagonal intermetallic compound Ti 3 Al. The obtained results are well consistent with the available experimental and theoretical data. The effect of pressure on all studied parameters was investigated. By the mechanical stability criteria under isotropic pressure, it is predicted that the compound is mechanically unstable at pressures above 71.4 GPa. Its ductility, anisotropy, and Debye temperature are enhanced with pressure.

scholarly journals Solid-State and Theoretical Investigations of Some Banister-Type Macrocycles with 2,2’-Aldoxime-1,1’-Biphenyl Units

2021 ◽  
Vol 9 ◽  
Author(s):  
Ioan Stroia ◽  
Ionuţ -Tudor Moraru ◽  
Maria Miclăuş ◽  
Ion Grosu ◽  
Claudia Lar ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Solid State ◽  
Density Functional ◽  
Alkali Metal Ions ◽  
Functional Theory ◽  
State Data ◽  
Supramolecular Associations ◽  
Theoretical Investigations ◽  
The Stability ◽  
Good Agreement

In the context of helical chirality, bridging of biphenyl units leads to banister-type compounds and the stability of the resulted atropisomers may increase dramatically if suitable changes are performed in the linker unit that coils around the biphenyl moiety. A rigorous density functional theory (DFT) study was conducted for macrocycles containing rigid oxime ether segments connected to the biphenyl backbone in order to determine how the rotation barriers are influenced by the presence of either a flexible oligoethyleneoxide or a more rigid m–xylylene component in the macrocycle. The calculated values for the racemization barrier were in good agreement with those obtained experimentally and confirm the benefit of introducing a more rigid unit in the macrocycle on the stability of atropisomers. Solid-state data were obtained and computed data were used to assess the contribution brought by supramolecular associations observed in the lattice to the stabilization of the crystal structure. Beside introducing rigidity in the linker, complexation of flexible macrocycles with alkali metal ions is also contributing to the stability of atropisomers, leading to values for the racemization barrier matching that of the rigid macrocycle. Using diethylammonium cation as guest for the macrocycle, a spectacular increase in the barrier to rotation was observed for the resulted pseudo[2]rotaxane.

First-principles calculations of the structural, elastic, mechanical, electronic and optical properties of monoclinic Hf4CuSi4

2020 ◽  
Vol 34 (06) ◽  
pp. 2050035
Author(s):  
Xia Xu ◽  
Wei Zeng ◽  
Fu-Sheng Liu ◽  
Zheng-Tang Liu ◽  
Qi-Jun Liu
Keyword(s):  
Optical Properties ◽  
Band Structure ◽  
First Principles ◽  
Density Functional ◽  
Mechanical Stability ◽  
Elastic Anisotropy ◽  
Structural Parameters ◽  
Functional Theory ◽  
Text Structures ◽  
Structure Density

In this paper, the structural, electronic, elastic, mechanical and optical properties of monoclinic [Formula: see text] are studied using the first-principles density functional theory (DFT). The calculated structural parameters are consistent with the experimental data. The elastic constants of [Formula: see text] structures are calculated, indicating that [Formula: see text] shows mechanical stability and elastic anisotropy. According to the [Formula: see text] and Poisson’s ratio, monoclinic [Formula: see text] shows a brittle manner. The energy band structure, density of states, charge transfers and bond populations are given. And the band structure shows that the material is a metal conductor. Moreover, the optical properties and optical anisotropy of [Formula: see text] are shown and analyzed.

First-Principle Study on the Structural Phase Transition, and Electronic Structures of Cobalt under Pressure

2015 ◽  
Vol 729 ◽  
pp. 15-20
Author(s):  
Hong Bo Zhu ◽  
Dun Qiang Tan ◽  
Zhi Huang Xiong
Keyword(s):  
Phase Transition ◽  
Electronic Structures ◽  
Density Functional ◽  
Structural Parameters ◽  
Structural Phase ◽  
First Principles Calculation ◽  
Functional Theory ◽  
Calculated Equilibrium ◽  
Theoretical Results ◽  
Good Agreement

The structural phase transitions and electronic structures of Co are investigated by using the first-principles calculation based on density-functional theory (DFT). Our calculated equilibrium structural parameters of Co are in good agreement with the available experimental data and other theoretical results. The calculated phase transition hcp-Co → fcc-Co at ca. 125.25 GPa. The magnetic moment of hcp-Co and fcc-Co drops to zero at 155 GPa and 77 GPa, respectively.

First-principles study on structural, elastic and thermal properties of γ-TiAl and α2-Ti3Al phases in TiAl-based alloy under high pressure

2017 ◽  
Vol 31 (11) ◽  
pp. 1750079 ◽  
Author(s):  
Chaoyan Zhang ◽  
Hua Hou ◽  
Yuhong Zhao ◽  
Xiaomin Yang ◽  
Yaqiong Guo
Keyword(s):  
High Pressure ◽  
Thermal Properties ◽  
Density Functional ◽  
Theoretical Data ◽  
Debye Model ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Two Phases ◽  
Calculated Equilibrium ◽  
Good Agreement

The structural, elastic and thermal properties of [Formula: see text]-TiAl and [Formula: see text]-Ti3Al phases in the TiAl-based alloy under pressure were reported using CASTEP program based on the density functional theory. The calculated equilibrium parameters and elastic constants are in good agreement with experimental and the available theoretical data. The results indicate that under the same pressure, the [Formula: see text] phase in the direction along [Formula: see text]-axis is easier to be compressed than the [Formula: see text] phase, while the compression along [Formula: see text]-axis of [Formula: see text] phase is larger than that of [Formula: see text] phase; when the pressure is below 20 GPa, both the two phases are elastically stable, but the [Formula: see text] phase have higher shear modulus and Young’s modulus, and the [Formula: see text] phase has better ductility and plasticity. Debye temperature, bulk modulus, thermal expansion coefficient and heat capacity of the [Formula: see text] phase and [Formula: see text] phase under high pressure and high temperature were also successfully calculated and compared using the quasi-harmonic Debye model in the present work.

Does Osmium Carbide Exist? Ab initio Investigation

2006 ◽  
Vol 987 ◽  
Author(s):  
M. Zemzemi ◽  
M. Hebbache ◽  
D. Zivkovic ◽  
L Stuparevic
Keyword(s):  
Mechanical Properties ◽  
Density Functional Theory ◽  
Transition Metals ◽  
Ab Initio ◽  
Density Functional ◽  
Ambient Pressure ◽  
Hexagonal Structure ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Good Agreement

AbstractTransition metals of the platinum group (Os, Ir, Pt, Ru, Re, Rh) do not form carbides and nitrides at ambient pressure. Osmium carbide seems to have been synthesized at zero pressure by Kempter and Nadler forty six years ago. According to the authors, OsC crystallizes in WC-type structure and has a hardness equal to 2000 kg mm-2. Up to date, no other experimental confirmation is available. We studied the electronic and mechanical properties of this hypothetical carbide using an approach based on the density-functional theory. We found that the work of the above mentioned authors is sound. The calculated lattice parameters are in good agreement with that given by those authors and a rough estimate also showed that the hardness given by them is reasonable. However, we found that the hexagonal structure of osmium carbide is electronically and mechanically unstable.

First-Principles Study on Electronic Structure, Elasticity, Debye Temperature and Anisotropy of Cubic KCaF3

2020 ◽  
Vol 999 ◽  
pp. 109-116
Author(s):  
Xing Liu ◽  
Jia Fu ◽  
Man Man Han ◽  
Kai Xin Sun ◽  
Sheng Li Wei
Keyword(s):  
Electronic Structure ◽  
Debye Temperature ◽  
First Principles ◽  
Density Functional ◽  
Elastic Moduli ◽  
Poisson Ratio ◽  
Structural Parameters ◽  
Functional Material ◽  
Covalent Bonds ◽  
Functional Theory

As a potential functional material in the perovskite family, the KCaF3 on electronic structure, elasticity, Debye temperature and anisotropy are studied based on density functional theory (DFT). Above all, the structural parameters of KCaF3 crystal are optimized. Then the elastic constants and Debye temperature are calculated. The results show that: (1) KCaF3 is composed of covalent bonds, in which the Ca-F bond is stronger than K-F. (2) Ca atom mainly contributes for the electronic properties of KCaF3. (3) The structural parameters of KCaF3 is in fair agreement with the experimental data. (4) The anisotropy of KCaF3 was analyzed from the pure and quasi waves, of which the longitudinal wave velocity in the direction of [100] is the larger than the others two directions ([110] and [111]). Finally, The homogenized elastic moduli (bulk modulus B, shear modulus G, Young's modulus E), Pugh and Poisson ratio, are obtained. This research is meaningful and thus to provides a good theoretical guidance for the design the new ABX3-type material with better performance.

scholarly journals Effet of edge fluorination and chlorination on structures, stability, electronic and charge transport properties of benzo[o]bistriphenyleno[2,1,12,11-efghi:2',1',12',11'-uvabc]ovalene molecule : DFT study.

2021 ◽  
Author(s):  
Marius Ousmanou Bouba ◽  
Fridolin Tchangnwa Nya ◽  
Christine Yvette Ngui ◽  
Jean Marie Ndjaka
Keyword(s):  
Experimental Data ◽  
Density Functional ◽  
Charge Carriers ◽  
Bandgap Energy ◽  
Electron Affinities ◽  
New Materials ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Theoretical Investigations ◽  
Good Agreement

Abstract We have investigated the structures, electronic properties, hole and electron mobilities of fluorinated and chlorinated nanographene of benzo[o]bistriphenyleno[2,1,12,11-efghi:2',1',12',11'-uvabc]ovalene (TCHG) molecules, us- ing the density functional theory (DFT) and Markus-Hush charge transfer theory. The calculated geometric parameters and the IR spectrum for chlorinated TCHG are in good agreement with the experimental data. Our theoretical investigations have shown that fluorination and chlorination significantly reduce the bandgap energy of TCHG. The obtained adiabatic electron affinities (AEAs) values are 2.76 and 2.93 eV respectively, indicating the air-stable materials. The calculation of charge carriers mobilities in chlorinated dimer shows that the mobility of the electrons is ten times that of the holes, suggesting an n-type behavior. We have shown that the fluorination and chlorination of TCHG are promising pathways for the design of new materials useful in optoelectronics

Electronic, Optical and Vibrational Properties of B3N3H6 from First-Principles Calculations

2021 ◽  
Author(s):  
Yun-Dan Gan ◽  
Han Qin ◽  
Fu-Sheng Liu ◽  
Zheng-Tang Liu ◽  
Cheng lu Jiang ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Local Density ◽  
Structural Parameters ◽  
Vibrational Properties ◽  
First Principles Calculations ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Conductivity Loss ◽  
Good Agreement

Abstract The electronic, optical and vibrational properties of B3N3H6 have been calculated by means of first-principles density functional theory (DFT) calculations within the generalized gradient approximation (GGA) and the local density approximation (LDA). The calculated structural parameters of B3N3H6 are in good agreement with experimental work. With the band structure and density of states (DOS), we have analyzed the optical properties including the complex dielectric function, refractive index, absorption, conductivity, loss function and reflectivity. By the contrast, it is found that on the (001) component and (100) component have obvious optical anisotropy. Moreover, the vibrational properties have been obtained and analyzed.

scholarly journals optPBE-vdW density functional theory study of liquid water and pressure-induced structural evolution in ice Ih

2017 ◽  
Vol 95 (11) ◽  
pp. 1205-1211 ◽  
Author(s):  
Xue Yong ◽  
John S. Tse ◽  
Niall J. English
Keyword(s):  
Density Functional ◽  
Structural Parameters ◽  
Structural Evolution ◽  
Hexagonal Structure ◽  
Density Functional Theory Study ◽  
Phonon Modes ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Crystal Transformation ◽  
Non Local

The accuracy of several local and non-local van der Waals (vdW) corrected exchange correlation functionals on the description of the effect of pressure on ice has been investigated. In a preliminary survey, the non-local vdW correction used in conjunction with the optPBE functional was shown to provide the best overall agreement on the structural parameters of ice Ih with experiments. More importantly, this combination reproduced correctly the recently observed crystal → crystal transformation in ice Ih at 80 K prior to amorphisation. The predicted transition pressure of 1.9 GPa is somewhat higher, showing that the current generation of vdW functionals are still not sufficiently accurate for the ice system. The existence of an intermediate crystalline state with a shear-hexagonal structure confirms the earlier prediction that the collapse of crystalline structure under compression originates from the softening of phonon modes in ice Ih’s basal plane.

Sign in / Sign up

Export Citation Format

Share Document