scholarly journals Group Theory Analysis to Study Phase Transitions of Quasi-2D Sr3Hf2O7

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 897
Author(s):  
Estelina Lora da Silva ◽  
Adeleh Mokhles Gerami ◽  
P. Neenu Lekshmi ◽  
Michel L. Marcondes ◽  
Lucy V. C. Assali ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Ground State ◽  
Density Functional ◽  
Structural Phase ◽  
Valence Band Maximum ◽  
Layered Perovskite ◽  
Partial Density ◽  
Study Phase ◽  
Ground State Structure ◽  
Potential Candidate

We present an ab-initio study performed in the framework of density functional theory, group-subgroup symmetry analysis and lattice dynamics, to probe the octahedral distortions, which occur during the structural phase transitions of the quasi-2D layered perovskite Sr3Hf2O7 compound. Such a system is characterized by a high-temperature I4/mmm centrosymmetric structure and a ground-state Cmc21 ferroelectric phase. We have probed potential candidate polymorphs that may form the I4/mmm → Cmc21 transition pathways, namely Fmm2, Ccce, Cmca and Cmcm. We found that the band gap widths increase as the symmetry decreases, with the ground-state structure presenting the largest gap width (∼5.95 eV). By probing the Partial Density of States, we observe a direct relation regarding the tilts and rotations of the oxygen perovskite cages as the transition occurs; these show large variations mostly of the O p-states which contribute mostly to the valence band maximum. Moreover, by analyzing the hyperfine parameters, namely the Electric Field Gradients and asymmetric parameters, we observe variations as the transition occurs, from which it is possible to identify the most plausible intermediate phases. We have also computed the macroscopic polarization and confirm that the Cmc21 phase is ferroelectric with a value of spontaneous polarization of 0.0478 C/m2. The ferroelectricity of the ground-state Cmc21 system arises due to a second order parameter related to the coupling of the rotation and tilts of the O perovskite cages together with the Sr displacements.

A density functional study of Rh13

2013 ◽  
Vol 91 (7) ◽  
pp. 591-597 ◽  
Author(s):  
Patrizia Calaminici ◽  
José M. Vásquez-Pérez ◽  
Diego A. Espíndola Velasco
Keyword(s):  
Molecular Dynamics ◽  
Ground State ◽  
Density Functional ◽  
Local Density ◽  
Structural Parameters ◽  
Functional Study ◽  
Ground State Structure ◽  
State Structure ◽  
Generalized Gradient ◽  
Density Functional Study

A density functional study was performed for the Rh13 cluster using the linear combination of Gaussian-type orbitals density functional theory (LCGTO-DFT) approach. The calculations employed both the local density approximation (LDA) as well as the generalized gradient approximation (GGA) in combination with a quasi-relativistic effective core potential (QECP). Initial structures for the geometry optimization were taken along Born–Oppenheimer molecular dynamics (BOMD) trajectories. The BOMD trajectories were performed at different temperatures and considered different potential energy surfaces (PES). As a result, several hundred isomers of the Rh13 cluster in different spin multiplicities were optimized with the aim to determine the lowest energy structures. All geometry optimizations were performed without any symmetry restriction. A vibrational analysis was performed to characterize these isomers. Structural parameters, relative stability energy, harmonic frequencies, binding energy, and most relevant Kohn–Sham (KS) molecular orbitals are reported. The obtained results are compared with available data from the literature. This study predicts a low symmetry biplanarlike structure as the ground-state structure of Rh13 with 11 unpaired electrons. This isomer was first noticed by inspection of first-principle Born–Oppenheimer molecular dynamics (BOMD) simulations between 300 and 600 K. This represents the most extensive theoretical study on the ground-state structure of the Rh13 cluster and underlines the importance of BOMD simulations to fully explore the PES landscapes of complicated systems.

A detailed first principle study on the structural, elastic, and electronic properties of indium arsenide (InAs) under induced pressure

2016 ◽  
Vol 94 (3) ◽  
pp. 254-261
Author(s):  
Kh. Kabita ◽  
M. Jameson ◽  
B.I. Sharma ◽  
R.K. Brojen ◽  
R.K. Thapa
Keyword(s):  
Electronic Properties ◽  
Indium Arsenide ◽  
Rock Salt ◽  
Density Functional ◽  
Structural Phase ◽  
Theoretical Data ◽  
Partial Density ◽  
Electronic Band ◽  
Zinc Blende ◽  
Salt Structure

An ab initio calculation of the structural, elastic, and electronic properties of indium arsenide (InAs) under induced pressure is investigated using density functional theory with modified Becke–Johnson potential within the generalised gradient approximation of the Perdew–Burke–Ernzerhof scheme. The lattice parameters are found to be in good agreement with experimental and other theoretical data. The pressure-induced structural phase transition of InAs zinc blende to rock salt structure is found to occur at 4.7 GPa pressure with a 17.2% of volume collapse. The elastic properties of both the zinc blende and rock salt structures at different pressures are studied. The electronic band structures at different pressures for both the structures are investigated using the total and partial density of states. The energy band gap of the InAs zinc blende phase is increased with increasing pressure while in rock salt the phase the conduction band crosses towards the valence band and thus shows metallic behaviour.

The Structure and Stability of C20 Dimer

2015 ◽  
Vol 1096 ◽  
pp. 228-231
Author(s):  
Ting Ting Dai ◽  
Pei Ying Huo ◽  
Ji Cai Yu ◽  
Huan Liu ◽  
Yan Xia Song ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Ground State ◽  
Electronic Structures ◽  
Density Functional ◽  
Ground State Structure ◽  
State Structure ◽  
Carbon Cage ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
The Stability

The possible geometrical and electronic structures of C20dimer are optimized by using the density functional theory at B3LYP/LANL2DZ level, stable structure of C20dimer are obtained. The stability of the ground state structure have been studied. The results showed that: there was a slight expansion in carbon cage of C20 dimer ; its chemical stability and thermal stability have been improved.

Theoretical Study of Structural, Elastic Properties and Phase Transitions of Cu2ZnSnS4

2014 ◽  
Vol 1058 ◽  
pp. 113-117 ◽  
Author(s):  
Yi Feng Zhao ◽  
Zu Ming Liu ◽  
De Cong Li
Keyword(s):  
Phase Transitions ◽  
Elastic Properties ◽  
Density Functional ◽  
Theoretical Work ◽  
Structure Stability ◽  
Ground State Structure ◽  
Preparation Technology ◽  
Functional Theory ◽  
Unstable Phase ◽  
Total Energies

The total energy, the electronic properties, phase transitions, and elastic properties of Cu2ZnSnS4(CZTS) in the three structures are investigated by first-principles calculations based on density functional theory. Results show that the total energies of stannite (ST) and primitive-mixed CuAu (PMCA) structures are higher than that of kesterite-type (KS), and the KS is the ground state structure. Relationships between enthalpy and pressure of the KS, ST and PMCA structure of CZTS are also investigated at 0 K, since the pressure can have profound impacts on the electronic structure, possible phase transitions and structure stability. And results also show that KS structure is always the most stable; ST is the second; and the PMCA structure is the most unstable; phase transitions of three structures could not occur in high pressure. The high ratios of shear modulus to bulk modulus (G/B) indicate that CZTS compounds in three types have ductile behaviors. The Poisson ratios for the three structures are from 0.27 to 0.31, which again proves that all structures of CZTS have better plasticity. The results can increase more hints about further research directions, and these effects can play an important role in future experimental preparation technology and theoretical work of CZTS materials.

Electronic Structure and Ground State Properties of A4[Ag4O4] (A=Na, K and Rb): A First-Principles Study

2013 ◽  
Vol 665 ◽  
pp. 43-48
Author(s):  
Rajagopalan Umamaheswari ◽  
M. Yogeswari ◽  
G. Kalpana
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Ground State ◽  
First Principles ◽  
Density Functional ◽  
Electronic Band Structure ◽  
First Principles Calculation ◽  
Partial Density ◽  
Electronic Band ◽  
Ground State Properties

The first-principles calculation within density functional theory is used to study in detail the electronic structure and ground state properties of alkali-metal oxoargenates A4[Ag4O4] (A= Na, K and Rb). The total energies calculated within the atomic sphere approximation (ASA) were used to determine the ground state properties such as equilibrium lattice parameter, c/a ratio, bulk modulus and cohesive energy. The theoretically calculated equilibrium lattice constants values are in well agreement with the available experimental values. The electronic band structures, total and partial density of states are calculated. The result of electronic band structure shows that the KAgO and RbAgO are direct band gap semiconductors with their gap lying between the Γ-Γ points, whereas NaAgO is found to be an indirect band gap semiconductor with its gap lying between Z-Γ points.

Structure and Stability of Osn (n=2-10) Clusters

2014 ◽  
Vol 1081 ◽  
pp. 84-87
Author(s):  
Xiu Rong Zhang ◽  
Fu Xing Zhang
Keyword(s):  
Density Functional Theory ◽  
Geometric Structure ◽  
Ground State ◽  
Relative Stability ◽  
Density Functional ◽  
Ground State Structure ◽  
State Structure ◽  
Functional Theory ◽  
Oscillation Effect ◽  
Ground State Structures

Geometric structure of Osn(n=2-10) clusters are optimized by using Density functional theory (DFT) in DMOL3 package. For the ground-state structure, relative stability are analyzed. The results show that: the ground-state structures of the cluster are plane structure when n=2-4, but the ground-state structures are stereostructure when n≥5. There exhibits the odd-even oscillation effect in stability and Os8cluster has the highest stability.

Structural Phase Transition and Electronic Properties of MgCe under High Pressure from First-Principles Calculations

2014 ◽  
Vol 577 ◽  
pp. 102-107
Author(s):  
Qiu Xiang Liu ◽  
De Ping Lu ◽  
Rui Jun Zhang ◽  
Lei Lu ◽  
Shi Fang Xie
Keyword(s):  
Phase Transition ◽  
Ground State ◽  
First Principles ◽  
Electronic Structures ◽  
Density Functional ◽  
High Pressures ◽  
Local Density ◽  
Structural Phase ◽  
First Principles Calculations ◽  
Functional Theory

The structural stability of MgCe under high pressures has been investigated by using the first-principles plane-wave pseudopotential density functional theory within the local density approximation (LDA). The obtained results predict that MgCe in the Ba structure is predicted to be the most stable structure corresponding to the ground state, because of lowest total energy. MgCe undergoes a pressure-induced phase transition from the Ba structure to B32 structure at 36 GPa. And no further transition is found up to 120 GPa. In addition, the electronic structures of four structures of MgCe are also calculated and discussed.

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