<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Kelkar, Tuhina</style></author><author><style face="normal" font="default" size="100%">Pal, Sourav</style></author><author><style face="normal" font="default" size="100%">Kanhere, Dilip G.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Density functional investigations of electronics structure and dehydrogenation reactions of Al- and Si-substituted magnesium hydride</style></title><secondary-title><style face="normal" font="default" size="100%">ChemPhysChem </style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">band structure</style></keyword><keyword><style  face="normal" font="default" size="100%">Density functional calculations</style></keyword><keyword><style  face="normal" font="default" size="100%">hydrides</style></keyword><keyword><style  face="normal" font="default" size="100%">Hydrogen storage</style></keyword><keyword><style  face="normal" font="default" size="100%">Thermodynamics</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2008</style></year><pub-dates><date><style  face="normal" font="default" size="100%">APR</style></date></pub-dates></dates><number><style face="normal" font="default" size="100%">6</style></number><publisher><style face="normal" font="default" size="100%">WILEY-V C H VERLAG GMBH</style></publisher><pub-location><style face="normal" font="default" size="100%">PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY</style></pub-location><volume><style face="normal" font="default" size="100%">9</style></volume><pages><style face="normal" font="default" size="100%">928-934</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;p&gt;{The effect on the hydrogen storage attributes of magnesium hydride (MgH2) of the substitution of Mg by varying fractions of Al and Si is investigated by an ab initio plane-wave pseuodopotential method based on density functional theory. Three supercells, namely, 2 x 2 x x 3 x 1 x 1 and 5 x 1 x 1 are used for generating configurations with varying amounts (fractions x=0.0625, 0.1, and 0.167) of impurities. The analyses of band structure and density of states (DOS) show that, when a Mg atom is replaced by Al, the band gap vanishes as the extra electron occupies the conduction band minimum. In the case of Si-substitution, additional states are generated within the band gap of pure MgH2-significontly reducing the gap in the process. The reduced band gaps cause the Mg-H bond to become more susceptible to dissociation. For all the fractions, the calculated reaction energies for the stepwise removal of H-2 molecules from Al- and Si-substituted MgH2 ore much lower than for H-2 removal from pure MgH2. The reduced stability is also reflected in the comparatively smaller heats of formation (Delta H-f) of the substituted MgH2 systems. Si causes greater destabilization of MgH2 than Al for each x. For fractions x = 0.167 of Al&lt;/p&gt;</style></abstract><issue><style face="normal" font="default" size="100%">6</style></issue><work-type><style face="normal" font="default" size="100%">Article</style></work-type><custom3><style face="normal" font="default" size="100%">Foreign</style></custom3><custom4><style face="normal" font="default" size="100%">3.138</style></custom4></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Kelkar, Tuhina</style></author><author><style face="normal" font="default" size="100%">Kanhere, Dilip G.</style></author><author><style face="normal" font="default" size="100%">Pal, Sourav</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">First principles calculations of thermal, equations of state and thermodynamical properties of MgH2 at finite temperatures</style></title><secondary-title><style face="normal" font="default" size="100%">Computational Materials Science</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">equation of state</style></keyword><keyword><style  face="normal" font="default" size="100%">Hydrogen storage</style></keyword><keyword><style  face="normal" font="default" size="100%">lattice dynamics</style></keyword><keyword><style  face="normal" font="default" size="100%">magnesium hydride</style></keyword><keyword><style  face="normal" font="default" size="100%">Thermodynamic properties</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2008</style></year><pub-dates><date><style  face="normal" font="default" size="100%">MAY</style></date></pub-dates></dates><number><style face="normal" font="default" size="100%">3</style></number><publisher><style face="normal" font="default" size="100%">ELSEVIER SCIENCE BV</style></publisher><pub-location><style face="normal" font="default" size="100%">PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS</style></pub-location><volume><style face="normal" font="default" size="100%">42</style></volume><pages><style face="normal" font="default" size="100%">510-516</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;p&gt;We present the first principles calculations of the thermodynamical properties of magnesium hydride (MgH2) over a temperature range of 0-1000 K. The phonon dispersions are determined within the density functional framework and are used to calculate the free energy of MgH2 within the quasiharmonic approximation (QHA) at each cell volume and temperature T. Using the free energies the thermal equation of state (EOS) is derived at several temperatures. From the thermal EOS structural parameters such as the equilibrium bell volume (V-0) and elastic properties, namely, bulk modulus (K-0) and its pressure derivative (K-0(')) are computed. The free energies are also used to calculate various thermodynamical properties within QHA. These include internal energy E, entropy S, specific heat capacity at constant pressure C-P, thermal pressure P-thermal(V,T) and volume thermal expansion Delta V/V (%). The good agreement of calculated values of S and Cp with experimental data exhibits that QHA can be used as a tool for calculating the thermodynamical properties of MgH2 over a wide temperature range. P-thermal(V,T) increases strongly with T at all the volumes but it is a slowly varying function of volume for T = 298-500 K. According to Karki [B.B. Karki, Am. Miner. 85 (2000) 1447] such volume based variations can be neglected and so it is possible to estimate the thermal EOS only with the knowledge of the measured P-thermal(V,T) versus temperature at ambient pressure and isothermal compression data at ambient temperature. Temperature dependence of Delta V/V(%) shows that V-0 increased with increase in temperature. However, the percentage decrease in K-0 superseded this percentage increase in V-0 even at temperatures moderately higher than 298 K. Therefore, we suggest application of temperature (T &amp;gt; 298 K) as an approach to enhance the hydrogen storage capacity of MgH2 because of its better compressibility at these temperatures. (C) 2007 Elsevier B.V. All rights reserved.&lt;/p&gt;</style></abstract><issue><style face="normal" font="default" size="100%">3</style></issue><work-type><style face="normal" font="default" size="100%">Article</style></work-type><custom3><style face="normal" font="default" size="100%">Foreign</style></custom3><custom4><style face="normal" font="default" size="100%">2.086</style></custom4></record></records></xml>