  An interatomic potential for high-pressure high-temperature (HPHT)
crystalline and liquid phases of sodium is created using a neural-network (NN)
representation of the ab initio potential energy surface. It is demonstrated
that the NN potential provides an ab initio quality description of multiple
properties of liquid sodium and bcc, fcc, cI16 crystal phases in the P-T region
up to 120 GPa and 1200 K. The unique combination of computational efficiency of
the NN potential and its ability to reproduce quantitatively experimental
properties of sodium in the wide P-T range enables molecular dynamics
simulations of physicochemical processes in HPHT sodium of unprecedented
quality.
