1. D. M. Teter, Geophysical Laboratory and Center for High Pressure Research, Carnegie Institution of Washington, Washington, DC 20015, USA, and Department of Materials Science and Engineering, Virginia Tech, Blacksburg, VA, 24061, USA.
2. R. J. Hemley, Geophysical Laboratory and Center for High Pressure Research, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, DC, 20015, USA.