scholarly journals First-principles calculations and experimental studies of XYZ2 thermoelectric compounds: detailed analysis of van der Waals interactions

2018 ◽  
Vol 6 (40) ◽  
pp. 19502-19519 ◽  
Author(s):  
Jan-Hendrik Pöhls ◽  
Zhe Luo ◽  
Umut Aydemir ◽  
Jon-Paul Sun ◽  
Shiqiang Hao ◽  
...  

van der Waals interactions enhanced the prediction of properties in layered thermoelectrics.

2020 ◽  
Vol 7 (10) ◽  
pp. 1540-1547
Author(s):  
Hao Gao ◽  
Cong Liu ◽  
Andreas Hermann ◽  
Richard J Needs ◽  
Chris J Pickard ◽  
...  

Abstract Helium and methane are major components of giant icy planets and are abundant in the universe. However, helium is the most inert element in the periodic table and methane is one of the most hydrophobic molecules, thus whether they can react with each other is of fundamental importance. Here, our crystal structure searches and first-principles calculations predict that a He3CH4 compound is stable over a wide range of pressures from 55 to 155 GPa and a HeCH4 compound becomes stable around 105 GPa. As nice examples of pure van der Waals crystals, the insertion of helium atoms changes the original packing of pure methane molecules and also largely hinders the polymerization of methane at higher pressures. After analyzing the diffusive properties during the melting of He3CH4 at high pressure and high temperature, in addition to a plastic methane phase, we have discovered an unusual phase which exhibits coexistence of diffusive helium and plastic methane. In addition, the range of the diffusive behavior within the helium-methane phase diagram is found to be much narrower compared to that of previously predicted helium-water compounds. This may be due to the weaker van der Waals interactions between methane molecules compared to those in helium-water compounds, and that the helium-methane compound melts more easily.


2014 ◽  
Vol 118 (48) ◽  
pp. 27843-27849 ◽  
Author(s):  
Shaoyuan Li ◽  
Jialei Hao ◽  
Feifei Li ◽  
Ziping Niu ◽  
Zhenpeng Hu ◽  
...  

2020 ◽  
Vol 22 (38) ◽  
pp. 21909-21918 ◽  
Author(s):  
Khaled Boukri ◽  
Tarik Ouahrani ◽  
Michael Badawi ◽  
Kamel Demmouche ◽  
Ruth Franco ◽  
...  

The rhombohedral layered MgIn2Se4 undergoes a pressure-induced phase transition to an inverse spinel one, loses its van der Waals interactions, and becomes more covalent.


2019 ◽  
Author(s):  
Henrik Pedersen ◽  
Björn Alling ◽  
Hans Högberg ◽  
Annop Ektarawong

Thin films of boron nitride (BN), particularly the sp<sup>2</sup>-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN) are interesting for several electronic applications given band gaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800 K and 1000-10000 Pa, respectively. In this letter, we use van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. We find that r-BN is the stable sp<sup>2</sup>-hybridized phase at CVD conditions, while h-BN is metastable. Thus, our calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sahib Hasan ◽  
Khagendra Baral ◽  
Neng Li ◽  
Wai-Yim Ching

AbstractChalcogenide semiconductors and glasses have many applications in the civil and military fields, especially in relation to their electronic, optical and mechanical properties for energy conversion and in enviormental materials. However, they are much less systemically studied and their fundamental physical properties for a large class chalcogenide semiconductors are rather scattered and incomplete. Here, we present a detailed study using well defined first-principles calculations on the electronic structure, interatomic bonding, optical, and mechanical properties for 99 bulk chalcogenides including thirteen of these crytals which have never been calculated. Due to their unique composition and structures, these 99 bulk chalcogenides are divided into two main groups. The first group contains 54 quaternary crystals with the structure composition (A2BCQ4) (A = Ag, Cu; B = Zn, Cd, Hg, Mg, Sr, Ba; C = Si, Ge, Sn; Q = S, Se, Te), while the second group contains scattered ternary and quaternary chalcogenide crystals with a more diverse composition (AxByCzQn) (A = Ag, Cu, Ba, Cs, Li, Tl, K, Lu, Sr; B = Zn, Cd, Hg, Al, Ga, In, P, As, La, Lu, Pb, Cu, Ag; C = Si, Ge, Sn, As, Sb, Bi, Zr, Hf, Ga, In; Q = S, Se, Te; $$\hbox {x} = 1$$ x = 1 , 2, 3; $$\hbox {y} = 0$$ y = 0 , 1, 2, 5; $$\hbox {z} = 0$$ z = 0 , 1, 2 and $$\hbox {n} = 3$$ n = 3 , 4, 5, 6, 9). Moreover, the total bond order density (TBOD) is used as a single quantum mechanical metric to characterize the internal cohesion of these crystals enabling us to correlate them with the calculated properties, especially their mechanical properties. This work provides a very large database for bulk chalcogenides crucial for the future theoretical and experimental studies, opening opportunities for study the properties and potential application of a wide variety of chalcogenides.


2018 ◽  
Vol 6 (11) ◽  
pp. 2830-2839 ◽  
Author(s):  
Gul Rehman ◽  
S. A. Khan ◽  
B. Amin ◽  
Iftikhar Ahmad ◽  
Li-Yong Gan ◽  
...  

Based on (hybrid) first-principles calculations, material properties (structural, electronic, vibrational, optical, and photocatalytic) of van der Waals heterostructures and their corresponding monolayers (transition metal dichalcogenides and MXenes) are investigated.


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