First-principles prediction of a new high pressure polymorph of the BaSi_2 compound

摘要

In this paper, we present a study of the structural stability of BaSi2 under high pressure based on first-principles calculations using the projector augmented wave method and generalized gradient approximation as implemented in the ABINIT code. The equations of state of three known polymorphs of BaSi2 and four candidate structures are calculated along with their structural parameters and their enthalpies of formation. A new polymorph of BaSi_2, not yet reported experimentally, is found to be more stable than all the other structures at high pressure and 0 K. It corresponds to the MgZn_2-type (h) hexagonal structure with hP12 Pearson symbol (space group: P6_3/mmc. The stiffness coefficients Bij and elastic properties including bulk modulus B_0 with its first and second pressure derivative, (B',B"), Young's modulus (E) and Poisson's ratio (u) are computed using the stress-strain method.