Quantum molecular dynamics study of expanded beryllium: evolution from warm dense matter to atomic fluid

Area of Science:

• Condensed matter physics
• Plasma physics
• Materials science

Background:

• Understanding material properties under extreme conditions is crucial for astrophysics and inertial confinement fusion.
• Beryllium's behavior at high temperatures and low densities is not well-characterized.
• Warm dense matter (WDM) regimes present unique challenges for theoretical modeling.

Purpose of the Study:

• Investigate the equation of state, electrical, and optical properties of expanded beryllium.
• Characterize the metal-to-nonmetal transition in beryllium under expansion.
• Validate quantum molecular dynamics (QMD) as a tool for WDM opacity calculations.

Main Methods:

• Quantum molecular dynamics (QMD) simulations were employed.
• Simulations covered densities 2-100 times lower than normal solid density.
• Temperatures ranged from 5000 K to 30000 K.
• Optical conductivity spectra were fitted using the Drude-Smith model.
• Electronic density of states was analyzed.
• Results were compared with standard opacity codes.

Main Results:

• Optical response shifted from simple metal to atomic fluid with decreasing density.
• Conducting electrons showed signs of localization at lower densities.
• A negative derivative of electrical resistivity with respect to temperature indicated a metal-to-nonmetal transition.
• QMD-derived Rosseland opacity validated standard opacity codes for WDM.

Conclusions:

• Expanded beryllium undergoes a metal-to-nonmetal transition at low densities.
• Electron localization is a key feature of this transition.
• QMD is a powerful and validated method for studying WDM properties and plasma models.