High pressure phase transformation in thorium carbide: A first principle study.

First principles calculations using full potential linearized augmented plane wave (FP-LAPW) method have been carried out to analyze structural, electronic and elastic properties of ThC under hydrostatic compression. Our calculations carried out within the generalized gradient approximation (GGA) predict a structural phase transition from rocksalt type (B1) phase to CsCl type cubic (B2) structure at ∼ 45 GPa. The same transition is predicted to occur at ∼ 35 GPa by the calculations performed within local density approximation (LDA). Various physical quantities such as equilibrium volume, bulk modulus, pressure derivative of bulk modulus and elastic constants determined for both the phases at zero pressure are compared with data available in literature. We find that at zero pressure the B2 structure is unstable elastically also. However, it emerges as elastically stable structure before it stabilizes energetically at high pressure. Further, the activation barrier between these structures has been calculated at various pressures. [ABSTRACT FROM AUTHOR]

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