Pressure-induced Phase Transition and Electronic Structure Evolution in Layered Semimetal HfTe2

Motivated by the recent experimental work, the pressure-induced structural transition of well-known two-dimensional (2D) 1T-HfTe2 was investigated up to 50 GPa through the advanced CALYPSO structure search technique combined with the first-principles calculations. Our calculations suggested that the 1T-HfTe2 will first transform to C2/m phase at 3.6 GPa with a volume reduction of 7.6% and then to P (6) over bar 2m phase at 9.6 GPa with a volume collapse of 4.6%. The occurrences of 3D C2/m and P (6) over bar 2m phases mainly originated from the enhanced Te-Te interlayer coupling and the drastic distortions of Hf-Te polyhedrons in P (3) over bar m1 phase under compression. Concomitantly, the coordination number of Hf atoms increased from six in P (3) over bar m1 to eight in C2/m and eventually to nine in P (6) over bar 2m at elevated pressure. The metallic and semimetallic nature of C2/m and P (6) over bar 2m phases were characterized, and the evidence of the reinforced covalent interactions of Te-Hf and Te-Te orbitals in these two novel high-pressure phases were manifested by the atom-projected electronic DOS and Bader charge.