Density functional and quasiparticle band-structure calculations forGaxAl1−xNandGaxIn1−xNalloys

2003 ◽  
Vol 68 (7) ◽  
Author(s):  
F. Sökeland ◽  
M. Rohlfing ◽  
P. Krüger ◽  
J. Pollmann
Keyword(s):  
Band Structure ◽  
Density Functional ◽  
Band Structure Calculations ◽  
Structure Calculations ◽  
Quasiparticle Band

Modeling alkali alanates for hydrogen storage by density-functional band-structure calculations

2005 ◽  
Vol 20 (12) ◽  
pp. 3199-3213 ◽  
Author(s):  
Ole Martin Løvvik ◽  
Ole Swang ◽  
Susanne M. Opalka
Keyword(s):  
Band Structure ◽  
Hydrogen Storage ◽  
Density Functional ◽  
State Density ◽  
Alkali Cations ◽  
Hydrogen Density ◽  
Local Coordination ◽  
Mixed Alkali ◽  
Band Structure Calculations ◽  
Structure Calculations

The alanates (complex aluminohydrides) have relatively high gravimetric hydrogen density and are among the most promising solid-state hydrogen-storage materials. In this work, the crystal structure and electronic structure of pure and mixed-alkali alanates were calculated by ground-state density-functional band-structure calculations. The results are in excellent correspondence with available experimental data. The properties of the pure alanates were compared, and the relatively high stability of the Li3AlH6 phase was pointed out as an important difference that may explain the difficulty of hydrogenating lithium alanate. The alkali alanates are nonmetallic with calculated band gaps around 5 eV and 2.5–3 eV for the tetra- and hexahydrides. The bonding was identified as ionic between the alkali cations and the aluminohydride complexes, while it is polar covalent within the complex. A broad range of hypothetical mixed-alkali alanate compounds was simulated, and four were found to be stable compared to the pure alanates and each other: LiNa2AlH6, K2LiAlH6, K2NaAlH6, and K2.5Na0.5AlH6. No mixed-alkali tetrahydrides were found to be stable, and this was explained by the local coordination within the different compounds. The only alkali alanate that seemed to be close to fulfilling the international hydrogen density targets was NaAlH4.

Reversible Iodine Intercalation into Tungsten Ditelluride

2020 ◽  
Author(s):  
Patrick Schmidt ◽  
Philipp Schneiderhan ◽  
Markus Ströbele ◽  
Carl P. Romao ◽  
H.-Jürgen Meyer
Keyword(s):  
Band Structure ◽  
Density Functional ◽  
Density Wave ◽  
Fused Silica ◽  
Orthorhombic Space Group ◽  
Functional Theory ◽  
Band Structure Calculations ◽  
Axis Length ◽  
A Charge ◽  
Structure Calculations

The new compound WTe2I was prepared by a reaction of WTe2 with iodine in a fused silica vessel at temperatures between 40 and 200 °C. Iodine atoms are intercalated into the van der Waals gap between tungsten ditelluride layers. As a result, the WTe2 layer separation and therefore the c-axis length is significantly increased, and the orthorhombic space group is preserved. Iodine atoms form planar layers between each tungsten ditelluride layer. Due to oxidation by iodine the semi-metallic nature of WTe2 is changed, as shown by comparative band structure calculations for WTe2 and WTe2I based on density functional theory. The calculated phonon band structure of WTe2I suggests a charge density wave instability at low temperature.<br>

Reversible Iodine Intercalation into Tungsten Ditelluride

2020 ◽  
Author(s):  
Patrick Schmidt ◽  
Philipp Schneiderhan ◽  
Markus Ströbele ◽  
Carl P. Romao ◽  
H.-Jürgen Meyer
Keyword(s):  
Band Structure ◽  
Density Functional ◽  
Density Wave ◽  
Fused Silica ◽  
Orthorhombic Space Group ◽  
Functional Theory ◽  
Band Structure Calculations ◽  
Axis Length ◽  
A Charge ◽  
Structure Calculations

The new compound WTe2I was prepared by a reaction of WTe2 with iodine in a fused silica vessel at temperatures between 40 and 200 °C. Iodine atoms are intercalated into the van der Waals gap between tungsten ditelluride layers. As a result, the WTe2 layer separation and therefore the c-axis length is significantly increased, and the orthorhombic space group is preserved. Iodine atoms form planar layers between each tungsten ditelluride layer. Due to oxidation by iodine the semi-metallic nature of WTe2 is changed, as shown by comparative band structure calculations for WTe2 and WTe2I based on density functional theory. The calculated phonon band structure of WTe2I suggests a charge density wave instability at low temperature.<br>

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