High-pressure phase diagram of gold from first-principles calculations: Converging to an isotropic atomic stacking order

Abstract

We reported the high pressure and temperature phase diagram of noble metal gold up to 500GPa and 7000K constructed from first-principles calculations. Using the unbiased multi-algorithm-collaborative (MAC) crystal structure prediction method, we discovered several metastable polymorphs of gold besides the previously known face-centered-cubic (fcc) structure. The phase boundaries of these polymorphs were located deliberately in the framework of quasi-harmonic approximation (QHA). The stability field of fcc-Au is almost identical to the experimental data. More importantly, we discovered and verified a new phase, the double hexagonal close-packed (dhcp) structure, before it transits to hcp under increasing compression. At room temperature, gold transforms from the fcc to the dhcp structure at 231.6GPa, and at further compression it transits to the hcp structure at 447.8GPa. From its elastic properties, an isotropy of atomic stacking order was observed in Au under increasing compression.