Quantum simulation of low-temperature metallic liquid hydrogen.

Area of Science:

• Condensed matter physics
• Quantum mechanics
• Materials science

Background:

• The melting temperature of solid hydrogen decreases with increasing pressure above ~65 GPa.
• Theoretical predictions suggest a low-temperature liquid state of hydrogen may be non-molecular and metallic.
• Experimental evidence for these predicted states remains limited.

Purpose of the Study:

• To investigate the behavior of hydrogen under high pressure using advanced computational methods.
• To determine the melting temperature of hydrogen as a function of pressure.
• To explore the potential for a low-temperature, non-molecular, metallic liquid phase in hydrogen.

Main Methods:

• Utilized ab initio methods incorporating the quantum motion of protons.
• Performed simulations of hydrogen at pressures ranging from 500 to 1,200 GPa.
• Compared results from simulations including quantum proton motion with those using classical nuclei.

Main Results:

• Identified an atomic solid phase of hydrogen stable from 500 to 800 GPa, melting below 200 K.
• Observed a stable metallic atomic liquid phase of hydrogen at temperatures as low as 50 K, from 800 to 1,200 GPa.
• Demonstrated that quantum proton motion is essential for achieving these low melting temperatures, unlike classical simulations.

Conclusions:

• Quantum effects significantly lower the melting temperature of hydrogen at high pressures.
• A metallic atomic liquid phase of hydrogen is predicted to be stable at low temperatures (50 K) and high pressures (up to 1,200 GPa).
• The inclusion of proton quantum motion is crucial for accurately modeling the phase diagram of hydrogen under extreme conditions.