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

摘要

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 2 X 10~(-5)and 5 X 10~(-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 H_2O [Goldman et al.,Phys.Rev.Lett.94,217801 (2005)] and NH_3 [Cavazzoni et al.,Science 283,44 (1999)],we conclude that high P,T superionic phases of electronegative element hydrides could be common.