Phase diagram of solid hydrogen

We present new results for the phase diagram of low-temperature high-pressure solid hydrogen, which are obtained using independent-particle and many-body wave function-based approaches. To discover the nature of phase III, density functional theory calculations within the meta-generalized gradient approximation by means of the strongly constrained and appropriately normed (SCAN) semilocal density functional are employed to investigate eleven molecular structures within wide pressure ranges of 100-500 GPa. The SCAN-DFT predicts two structures of C2/c and P6₁22 as the best candidates for phase III. We employ the diffusion Monte Carlo (DMC) method to verify the stability of competitive phases which requires an accurate description of exchange interaction. Our DMC results indicate that the optimised percentage of exact-exchange in many-body wave function equals to 40%. We name the corresponding exchange and correlation functional as PBE₁. The PBE₁-predicted phase diagram shows that the phase III of high-pressure solid hydrogen is polymorphic [1].

References:
[1] Sam Azadi, and T. D. Kuehne, Phys. Rev. B 100 (15), 155103 (2019)