First principles simulation of a superionic phase of hydrogen fluoride (HF) at high pressures and temperatures

We have conducted ab initio molecular dynamics simulations of hydrogen fluoride (HF) at pressures of 5-66 GPa along the 900 K isotherm. We predict a superionic phase at 33 GPa, where the fluorine atoms are fixed in a bcc lattice while the hydrogen atoms diffuse rapidly with a diffusion constant between 2x10(-5) and 5x10(-5)cm(2)/s. We find that a transformation from asymmetric to symmetric hydrogen bonding occurs in HF at 66 GPa and 900 K. With superionic HF we have discovered a model system where symmetric hydrogen bonding occurs at experimentally achievable conditions. Given previous results on superionic H2O [Goldman , Phys. Rev. Lett. 94, 217801 (2005)] and NH3 [Cavazzoni , Science 283, 44 (1999)], we conclude that high P, T superionic phases of electronegative element hydrides could be common. (c) 2006 American Institute of Physics.