01488nas a2200169   4500008004100000245011300041210006900154260001200223300001400235490000700249520089100256100002401147700001901171700002701190700002301217856007801240       2002                        eng d00aCalculation of Thermodynamic, Electronic, and Optical Properties of Monoclinic Mg<sub>2</sub>NiH<sub>4</sub>0 aCalculation of Thermodynamic Electronic and Optical Properties o  c04/2002  a4879-48850 v913 a<p><em>Ab initio</em> total-energy density functional theory is used to investigate the low temperature (LT) monoclinic form of Mg<sub>2</sub>NiH<sub>4</sub>. The calculated minimum energy geometry of LT&nbsp;Mg<sub>2</sub>NiH<sub>4</sub> is close to that determined from neutron diffraction data, and the NiH<sub>4</sub> complex is close to a regular tetrahedron. The enthalpies of the phase change to high temperature (HT) pseudo-cubic&nbsp;Mg<sub>2</sub>NiH<sub>4</sub> and of hydrogen absorption by Mg<sub>2</sub>Ni are calculated and compared with experimental values. LT&nbsp;Mg<sub>2</sub>NiH<sub>4</sub> is found to be a semiconductor with an indirect band gap of 1.4 eV. The optical dielectric function of LT Mg<sub>2</sub>NiH<sub>4</sub> differs somewhat from that of the HT phase. A calculated thin film transmittance spectrum is consistent with an experimental spectrum.</p>1 aMyers, Whittier, R.1 aWang, Lin-Wang1 aRichardson, Thomas, J.1 aRubin, Michael, D.  uhttps://facades.lbl.gov/publications/calculation-thermodynamic-electronic