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The structural, electronic, and elastic properties of ScN and ScP in NaCl (B 1 phase) and CsCl (B 2 phase) structures and the phonon dispersion at ambient and high pressure, close to phase transition, have been investigated by using first-principles pseudopotential method in the framework of density functional theory with the generalized gradient approximation. It is found that both compounds are stable in B 1 phase at ambient pressure and undergo a structural phase transition to B 2 phase at 368.76 and 247.56 GPa, respectively. ScN is a semiconductor and ScP is semimetallic at ambient pressure (B 1 phase), whereas both the compounds are metallic at high pressure (B 2 phase). The calculated lattice parameter (a), bulk modulus (B), and their first-order pressure derivative (B 0 ) are in good agreement with previous calculations. The elastic constants (C 11 , C 12 , and C 44 ) have been calculated in both phases. We also report the phonon structure of these compounds at ambient and close to the phase-transition pressure and compared among themselves. It is shown that their phonon structures are consistent with electronic properties at ambient and high pressures. Near B 1 -B 2 transition, the LA mode at X-point softens considerably leading to structural instability.

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