1. Materials Science and Technology Division; Los Alamos National Laboratory; Los Alamos NM 87545 USA
2. Theoretical Division; Los Alamos National Laboratory; Los Alamos NM 87545 USA
3. Department of Mechanical Engineering, Department of Materials; University of California; Santa Barbara CA 93106 USA
4. Department of Mechanical & Materials Engineering; University of Nebraska-Lincoln; Lincoln NE 68583 USA